[Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Tristan Gingold]

Hi,

the code to call expand_main_function currently only checks DECL_NAME.  This leads
to a hack in ada/gcc-interface/utils.c to handle the gnatbind generated file that could
declare:

package ada_main is
…
   function my_main
     (argc : Integer;
      argv : System.Address;
      envp : System.Address)
      return Integer;
   pragma Export (C, my_main, "main");
…
end ada_main;

But expand_main_function is also called for function whose name is main but assembly name isn't.  Eg:

package pkg is
   procedure main;
end pkg;

So I think we should consider the assembler name is set, otherwise the decl name.

Manually tested on ia64-hp-openvms (where this issue was discovered).
No C regressions for x86_64-darwin.

Ok for trunk ?

Tristan.

gcc/
2012-03-14  Tristan Gingold  <gingold@adacore.com>

	* cfgexpand.c (gimple_expand_cfg): Consider the assembly name
	to call expand_main_function.

gcc/ada/
2012-03-14  Tristan Gingold  <gingold@adacore.com>

	* gcc-interface/utils.c (create_subprog_decl): Do not override
	DECL_NAME if asm_name is set.


diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index 2f38bb4..8693876 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -4501,8 +4501,12 @@ gimple_expand_cfg (void)
   /* If this function is `main', emit a call to `__main'
      to run global initializers, etc.  */
   if (DECL_NAME (current_function_decl)
-      && MAIN_NAME_P (DECL_NAME (current_function_decl))
-      && DECL_FILE_SCOPE_P (current_function_decl))
+      && DECL_FILE_SCOPE_P (current_function_decl)
+      && main_identifier_node != NULL_TREE
+      && ((!DECL_ASSEMBLER_NAME_SET_P (current_function_decl)
+	   && MAIN_NAME_P (DECL_NAME (current_function_decl)))
+	  || decl_assembler_name_equal (current_function_decl,
+					main_identifier_node)))
     expand_main_function ();
 
   /* Initialize the stack_protect_guard field.  This must happen after the

diff --git a/gcc/ada/gcc-interface/utils.c b/gcc/ada/gcc-interface/utils.c
index 7383358..81a1a0a 100644
--- a/gcc/ada/gcc-interface/utils.c
+++ b/gcc/ada/gcc-interface/utils.c
@@ -1899,18 +1899,7 @@ create_subprog_decl (tree subprog_name, tree asm_name, tree subprog_type,
   DECL_RESULT (subprog_decl) = result_decl;
 
   if (asm_name)
-    {
-      SET_DECL_ASSEMBLER_NAME (subprog_decl, asm_name);
-
-      /* The expand_main_function circuitry expects "main_identifier_node" to
-	 designate the DECL_NAME of the 'main' entry point, in turn expected
-	 to be declared as the "main" function literally by default.  Ada
-	 program entry points are typically declared with a different name
-	 within the binder generated file, exported as 'main' to satisfy the
-	 system expectations.  Force main_identifier_node in this case.  */
-      if (asm_name == main_identifier_node)
-	DECL_NAME (subprog_decl) = main_identifier_node;
-    }
+    SET_DECL_ASSEMBLER_NAME (subprog_decl, asm_name);
 
   /* Add this decl to the current binding level.  */
   gnat_pushdecl (subprog_decl, gnat_node);

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Richard Guenther]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 3764 bytes --]

On Wed, 14 Mar 2012, Tristan Gingold wrote:

> Hi,
> 
> the code to call expand_main_function currently only checks DECL_NAME.  This leads
> to a hack in ada/gcc-interface/utils.c to handle the gnatbind generated file that could
> declare:
> 
> package ada_main is
> Â…
>    function my_main
>      (argc : Integer;
>       argv : System.Address;
>       envp : System.Address)
>       return Integer;
>    pragma Export (C, my_main, "main");
> Â…
> end ada_main;
> 
> But expand_main_function is also called for function whose name is main but assembly name isn't.  Eg:
> 
> package pkg is
>    procedure main;
> end pkg;
> 
> So I think we should consider the assembler name is set, otherwise the decl name.
> 
> Manually tested on ia64-hp-openvms (where this issue was discovered).
> No C regressions for x86_64-darwin.
> 
> Ok for trunk ?

There are more checks for MAIN_NAME_P, so this certainly isn't enough.
And if it is a good idea then the whole check, whether a FUNCTION_DECL
is considered 'main' should be put into a function in tree.[ch] and
used everywhere.  Note that what is 'main' is controlled by
main_identifier_node, controlled by frontends.  So - why is that not
enough to control for Ada?

Richard.

> Tristan.
> 
> gcc/
> 2012-03-14  Tristan Gingold  <gingold@adacore.com>
> 
> 	* cfgexpand.c (gimple_expand_cfg): Consider the assembly name
> 	to call expand_main_function.
> 
> gcc/ada/
> 2012-03-14  Tristan Gingold  <gingold@adacore.com>
> 
> 	* gcc-interface/utils.c (create_subprog_decl): Do not override
> 	DECL_NAME if asm_name is set.
> 
> 
> diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
> index 2f38bb4..8693876 100644
> --- a/gcc/cfgexpand.c
> +++ b/gcc/cfgexpand.c
> @@ -4501,8 +4501,12 @@ gimple_expand_cfg (void)
>    /* If this function is `main', emit a call to `__main'
>       to run global initializers, etc.  */
>    if (DECL_NAME (current_function_decl)
> -      && MAIN_NAME_P (DECL_NAME (current_function_decl))
> -      && DECL_FILE_SCOPE_P (current_function_decl))
> +      && DECL_FILE_SCOPE_P (current_function_decl)
> +      && main_identifier_node != NULL_TREE
> +      && ((!DECL_ASSEMBLER_NAME_SET_P (current_function_decl)
> +	   && MAIN_NAME_P (DECL_NAME (current_function_decl)))
> +	  || decl_assembler_name_equal (current_function_decl,
> +					main_identifier_node)))
>      expand_main_function ();
>  
>    /* Initialize the stack_protect_guard field.  This must happen after the
> 
> diff --git a/gcc/ada/gcc-interface/utils.c b/gcc/ada/gcc-interface/utils.c
> index 7383358..81a1a0a 100644
> --- a/gcc/ada/gcc-interface/utils.c
> +++ b/gcc/ada/gcc-interface/utils.c
> @@ -1899,18 +1899,7 @@ create_subprog_decl (tree subprog_name, tree asm_name, tree subprog_type,
>    DECL_RESULT (subprog_decl) = result_decl;
>  
>    if (asm_name)
> -    {
> -      SET_DECL_ASSEMBLER_NAME (subprog_decl, asm_name);
> -
> -      /* The expand_main_function circuitry expects "main_identifier_node" to
> -	 designate the DECL_NAME of the 'main' entry point, in turn expected
> -	 to be declared as the "main" function literally by default.  Ada
> -	 program entry points are typically declared with a different name
> -	 within the binder generated file, exported as 'main' to satisfy the
> -	 system expectations.  Force main_identifier_node in this case.  */
> -      if (asm_name == main_identifier_node)
> -	DECL_NAME (subprog_decl) = main_identifier_node;
> -    }
> +    SET_DECL_ASSEMBLER_NAME (subprog_decl, asm_name);
>  
>    /* Add this decl to the current binding level.  */
>    gnat_pushdecl (subprog_decl, gnat_node);
> 
> 
> 

-- 
Richard Guenther <rguenther@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Tristan Gingold]

On Mar 14, 2012, at 5:08 PM, Richard Guenther wrote:

> On Wed, 14 Mar 2012, Tristan Gingold wrote:
> 
>> Hi,
>> 
>> the code to call expand_main_function currently only checks DECL_NAME.  This leads
>> to a hack in ada/gcc-interface/utils.c to handle the gnatbind generated file that could
>> declare:
>> 
>> package ada_main is
>> …
>>   function my_main
>>     (argc : Integer;
>>      argv : System.Address;
>>      envp : System.Address)
>>      return Integer;
>>   pragma Export (C, my_main, "main");
>> …
>> end ada_main;
>> 
>> But expand_main_function is also called for function whose name is main but assembly name isn't.  Eg:
>> 
>> package pkg is
>>   procedure main;
>> end pkg;
>> 
>> So I think we should consider the assembler name is set, otherwise the decl name.
>> 
>> Manually tested on ia64-hp-openvms (where this issue was discovered).
>> No C regressions for x86_64-darwin.
>> 
>> Ok for trunk ?
> 
> There are more checks for MAIN_NAME_P, so this certainly isn't enough.
> And if it is a good idea then the whole check, whether a FUNCTION_DECL
> is considered 'main' should be put into a function in tree.[ch] and
> used everywhere.  Note that what is 'main' is controlled by
> main_identifier_node, controlled by frontends.  So - why is that not
> enough to control for Ada?

Indeed, I think we could handle this issue in gigi for Ada.  (I also think
we don't want to handle crazy C code such as 'int my_main () asm ("main")'.

But, unless I missed something, doing this in gigi won't work with LTO.

Will write a predicate in tree.[ch].

Thank you for your comments,
Tristan.

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Richard Guenther]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1973 bytes --]

On Wed, 14 Mar 2012, Tristan Gingold wrote:

> 
> On Mar 14, 2012, at 5:08 PM, Richard Guenther wrote:
> 
> > On Wed, 14 Mar 2012, Tristan Gingold wrote:
> > 
> >> Hi,
> >> 
> >> the code to call expand_main_function currently only checks DECL_NAME.  This leads
> >> to a hack in ada/gcc-interface/utils.c to handle the gnatbind generated file that could
> >> declare:
> >> 
> >> package ada_main is
> >> Â…
> >>   function my_main
> >>     (argc : Integer;
> >>      argv : System.Address;
> >>      envp : System.Address)
> >>      return Integer;
> >>   pragma Export (C, my_main, "main");
> >> Â…
> >> end ada_main;
> >> 
> >> But expand_main_function is also called for function whose name is main but assembly name isn't.  Eg:
> >> 
> >> package pkg is
> >>   procedure main;
> >> end pkg;
> >> 
> >> So I think we should consider the assembler name is set, otherwise the decl name.
> >> 
> >> Manually tested on ia64-hp-openvms (where this issue was discovered).
> >> No C regressions for x86_64-darwin.
> >> 
> >> Ok for trunk ?
> > 
> > There are more checks for MAIN_NAME_P, so this certainly isn't enough.
> > And if it is a good idea then the whole check, whether a FUNCTION_DECL
> > is considered 'main' should be put into a function in tree.[ch] and
> > used everywhere.  Note that what is 'main' is controlled by
> > main_identifier_node, controlled by frontends.  So - why is that not
> > enough to control for Ada?
> 
> Indeed, I think we could handle this issue in gigi for Ada.  (I also think
> we don't want to handle crazy C code such as 'int my_main () asm ("main")'.
> 
> But, unless I missed something, doing this in gigi won't work with LTO.

Well.  To make this work in LTO the "main" function (thus, the program
entry point) should be marked at cgraph level and all users of
MAIN_NAME_P should instead check a flag on the cgraph node.

> Will write a predicate in tree.[ch].

Please instead transition "main-ness" to the cgraph.

Thanks,
Richard.

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Tristan Gingold]

On Mar 15, 2012, at 10:37 AM, Richard Guenther wrote:

> On Wed, 14 Mar 2012, Tristan Gingold wrote:
> 
>> 
>> On Mar 14, 2012, at 5:08 PM, Richard Guenther wrote:
>> 
>>> On Wed, 14 Mar 2012, Tristan Gingold wrote:
>>> 
>>>> Hi,
>>>> 
>>>> the code to call expand_main_function currently only checks DECL_NAME.  This leads
>>>> to a hack in ada/gcc-interface/utils.c to handle the gnatbind generated file that could
>>>> declare:
>>>> 
>>>> package ada_main is
>>>> …
>>>>  function my_main
>>>>    (argc : Integer;
>>>>     argv : System.Address;
>>>>     envp : System.Address)
>>>>     return Integer;
>>>>  pragma Export (C, my_main, "main");
>>>> …
>>>> end ada_main;
>>>> 
>>>> But expand_main_function is also called for function whose name is main but assembly name isn't.  Eg:
>>>> 
>>>> package pkg is
>>>>  procedure main;
>>>> end pkg;
>>>> 
>>>> So I think we should consider the assembler name is set, otherwise the decl name.
>>>> 
>>>> Manually tested on ia64-hp-openvms (where this issue was discovered).
>>>> No C regressions for x86_64-darwin.
>>>> 
>>>> Ok for trunk ?
>>> 
>>> There are more checks for MAIN_NAME_P, so this certainly isn't enough.
>>> And if it is a good idea then the whole check, whether a FUNCTION_DECL
>>> is considered 'main' should be put into a function in tree.[ch] and
>>> used everywhere.  Note that what is 'main' is controlled by
>>> main_identifier_node, controlled by frontends.  So - why is that not
>>> enough to control for Ada?
>> 
>> Indeed, I think we could handle this issue in gigi for Ada.  (I also think
>> we don't want to handle crazy C code such as 'int my_main () asm ("main")'.
>> 
>> But, unless I missed something, doing this in gigi won't work with LTO.
> 
> Well.  To make this work in LTO the "main" function (thus, the program
> entry point) should be marked at cgraph level and all users of
> MAIN_NAME_P should instead check a flag on the cgraph node.
> 
>> Will write a predicate in tree.[ch].
> 
> Please instead transition "main-ness" to the graph.

Ok, I will explore this way.

Tristan.

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Tristan Gingold]

On Mar 15, 2012, at 10:37 AM, Richard Guenther wrote:

> On Wed, 14 Mar 2012, Tristan Gingold wrote:
[…]

> 
> Well.  To make this work in LTO the "main" function (thus, the program
> entry point) should be marked at cgraph level and all users of
> MAIN_NAME_P should instead check a flag on the cgraph node.
> 
>> Will write a predicate in tree.[ch].
> 
> Please instead transition "main-ness" to the graph.

Hi,

here is the patch I wrote.  Does it match what you had in mind ?

main_identifier_node is now set in tree.c

I haven't changed MAIN_NAME_P uses in c-decl.c and cp/decl.c (obviously).
I haven't yet checked beyond simple build.

Tristan.

diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
index 89f5438..c575e97 100644
--- a/gcc/ada/gcc-interface/trans.c
+++ b/gcc/ada/gcc-interface/trans.c
@@ -622,8 +622,6 @@ gigi (Node_Id gnat_root, int max_gnat_node, int number_name ATTRIBUTE_UNUSED,
 		       integer_type_node, NULL_TREE, true, false, true, false,
 		       NULL, Empty);
 
-  main_identifier_node = get_identifier ("main");
-
   /* Install the builtins we might need, either internally or as
      user available facilities for Intrinsic imports.  */
   gnat_install_builtins ();
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index b83f45b..5d05d8a 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -5094,8 +5094,6 @@ c_common_nodes_and_builtins (void)
   if (!flag_preprocess_only)
     c_define_builtins (va_list_ref_type_node, va_list_arg_type_node);
 
-  main_identifier_node = get_identifier ("main");
-
   /* Create the built-in __null node.  It is important that this is
      not shared.  */
   null_node = make_node (INTEGER_CST);
diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index bd21169..7a7a774 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -4513,9 +4513,8 @@ gimple_expand_cfg (void)
 
   /* If this function is `main', emit a call to `__main'
      to run global initializers, etc.  */
-  if (DECL_NAME (current_function_decl)
-      && MAIN_NAME_P (DECL_NAME (current_function_decl))
-      && DECL_FILE_SCOPE_P (current_function_decl))
+  if (DECL_FILE_SCOPE_P (current_function_decl)
+      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
     expand_main_function ();
 
   /* Initialize the stack_protect_guard field.  This must happen after the
diff --git a/gcc/cgraph.c b/gcc/cgraph.c
index 9cc3690..528fd19 100644
--- a/gcc/cgraph.c
+++ b/gcc/cgraph.c
@@ -2766,7 +2766,7 @@ cgraph_propagate_frequency_1 (struct cgraph_node *node, void *data)
 	  /* It makes sense to put main() together with the static constructors.
 	     It will be executed for sure, but rest of functions called from
 	     main are definitely not at startup only.  */
-	  if (MAIN_NAME_P (DECL_NAME (edge->caller->decl)))
+	  if (cgraph_main_function_p (edge->caller))
 	    d->only_called_at_startup = 0;
           d->only_called_at_exit &= edge->caller->only_called_at_exit;
 	}
diff --git a/gcc/cgraph.h b/gcc/cgraph.h
index 191364c..4db3417 100644
--- a/gcc/cgraph.h
+++ b/gcc/cgraph.h
@@ -101,6 +101,9 @@ struct GTY(()) cgraph_local_info {
 
   /* True if the function may enter serial irrevocable mode.  */
   unsigned tm_may_enter_irr : 1;
+
+  /* True if the function is the program entry point (main in C).  */
+  unsigned main_function : 1;
 };
 
 /* Information about the function that needs to be computed globally
@@ -790,6 +793,13 @@ cgraph_next_function_with_gimple_body (struct cgraph_node *node)
   return NULL;
 }
 
+/* Return true iff NODE is the main function (main in C).  */
+static inline bool
+cgraph_main_function_p (struct cgraph_node *node)
+{
+  return node->local.main_function;
+}
+
 /* Walk all functions with body defined.  */
 #define FOR_EACH_FUNCTION_WITH_GIMPLE_BODY(node) \
    for ((node) = cgraph_first_function_with_gimple_body (); (node); \
diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
index 516f187..4a59f63 100644
--- a/gcc/cgraphunit.c
+++ b/gcc/cgraphunit.c
@@ -346,6 +346,10 @@ cgraph_finalize_function (tree decl, bool nested)
   notice_global_symbol (decl);
   node->local.finalized = true;
   node->lowered = DECL_STRUCT_FUNCTION (decl)->cfg != NULL;
+  node->local.main_function =
+    DECL_FILE_SCOPE_P (decl)
+    && ((!DECL_ASSEMBLER_NAME_SET_P (decl) && MAIN_NAME_P (DECL_NAME (decl)))
+	|| decl_assembler_name_equal (decl, main_identifier_node));
 
   if (cgraph_decide_is_function_needed (node, decl))
     cgraph_mark_needed_node (node);
diff --git a/gcc/config/i386/cygming.h b/gcc/config/i386/cygming.h
index 2eccda9..8ac169e 100644
--- a/gcc/config/i386/cygming.h
+++ b/gcc/config/i386/cygming.h
@@ -360,7 +360,8 @@ do {						\
 
 #undef PROFILE_HOOK
 #define PROFILE_HOOK(LABEL)						\
-  if (MAIN_NAME_P (DECL_NAME (current_function_decl)))			\
+  if (DECL_FILE_SCOPE_P (current_function_decl)				\
+      && cgraph_main_function_p (cgraph_get_node (current_function_decl))) \
     {									\
       emit_call_insn (gen_rtx_CALL (VOIDmode,				\
 	gen_rtx_MEM (FUNCTION_MODE,					\
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 78a366e..5a3a712 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -9509,9 +9509,8 @@ ix86_minimum_incoming_stack_boundary (bool sibcall)
   /* Stack at entrance of main is aligned by runtime.  We use the
      smallest incoming stack boundary. */
   if (incoming_stack_boundary > MAIN_STACK_BOUNDARY
-      && DECL_NAME (current_function_decl)
-      && MAIN_NAME_P (DECL_NAME (current_function_decl))
-      && DECL_FILE_SCOPE_P (current_function_decl))
+      && DECL_FILE_SCOPE_P (current_function_decl)
+      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
     incoming_stack_boundary = MAIN_STACK_BOUNDARY;
 
   return incoming_stack_boundary;
diff --git a/gcc/config/pdp11/pdp11.c b/gcc/config/pdp11/pdp11.c
index 42e3af0..aa38903 100644
--- a/gcc/config/pdp11/pdp11.c
+++ b/gcc/config/pdp11/pdp11.c
@@ -240,7 +240,9 @@ pdp11_expand_prologue (void)
 
   /* If we are outputting code for main, the switch FPU to the
      right mode if TARGET_FPU.  */
-  if (MAIN_NAME_P (DECL_NAME (current_function_decl)) && TARGET_FPU)
+  if (TARGET_FPU
+      && DECL_FILE_SCOPE_P (current_function_decl)
+      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
     {
       emit_insn (gen_setd ());
       emit_insn (gen_seti ());
diff --git a/gcc/fortran/trans-decl.c b/gcc/fortran/trans-decl.c
index 8a1dd2e..6a1a494 100644
--- a/gcc/fortran/trans-decl.c
+++ b/gcc/fortran/trans-decl.c
@@ -4922,7 +4922,6 @@ create_main_function (tree fndecl)
   tmp =  build_function_type_list (integer_type_node, integer_type_node,
 				   build_pointer_type (pchar_type_node),
 				   NULL_TREE);
-  main_identifier_node = get_identifier ("main");
   ftn_main = build_decl (input_location, FUNCTION_DECL,
       			 main_identifier_node, tmp);
   DECL_EXTERNAL (ftn_main) = 0;
diff --git a/gcc/ipa-split.c b/gcc/ipa-split.c
index 9dddf39..595330e 100644
--- a/gcc/ipa-split.c
+++ b/gcc/ipa-split.c
@@ -1409,7 +1409,7 @@ execute_split_functions (void)
 	fprintf (dump_file, "Not splitting: noreturn/malloc function.\n");
       return 0;
     }
-  if (MAIN_NAME_P (DECL_NAME (current_function_decl)))
+  if (cgraph_main_function_p (node))
     {
       if (dump_file)
 	fprintf (dump_file, "Not splitting: main function.\n");
diff --git a/gcc/ipa.c b/gcc/ipa.c
index 388291a..f9dc42d 100644
--- a/gcc/ipa.c
+++ b/gcc/ipa.c
@@ -639,7 +639,7 @@ cgraph_externally_visible_p (struct cgraph_node *node,
   else if (!whole_program)
     return true;
 
-  if (MAIN_NAME_P (DECL_NAME (node->decl)))
+  if (cgraph_main_function_p (node))
     return true;
 
   return false;
diff --git a/gcc/lto-cgraph.c b/gcc/lto-cgraph.c
index 5e899bc..34bcc55 100644
--- a/gcc/lto-cgraph.c
+++ b/gcc/lto-cgraph.c
@@ -502,6 +502,7 @@ lto_output_node (struct lto_simple_output_block *ob, struct cgraph_node *node,
   bp_pack_value (&bp, node->local.versionable, 1);
   bp_pack_value (&bp, node->local.can_change_signature, 1);
   bp_pack_value (&bp, node->local.redefined_extern_inline, 1);
+  bp_pack_value (&bp, node->local.main_function, 1);
   bp_pack_value (&bp, node->needed, 1);
   bp_pack_value (&bp, node->address_taken, 1);
   bp_pack_value (&bp, node->abstract_and_needed, 1);
@@ -904,6 +905,7 @@ input_overwrite_node (struct lto_file_decl_data *file_data,
   node->local.versionable = bp_unpack_value (bp, 1);
   node->local.can_change_signature = bp_unpack_value (bp, 1);
   node->local.redefined_extern_inline = bp_unpack_value (bp, 1);
+  node->local.main_function = bp_unpack_value (bp, 1);
   node->needed = bp_unpack_value (bp, 1);
   node->address_taken = bp_unpack_value (bp, 1);
   node->abstract_and_needed = bp_unpack_value (bp, 1);
diff --git a/gcc/lto/lto-lang.c b/gcc/lto/lto-lang.c
index 999db8b..a44a35f 100644
--- a/gcc/lto/lto-lang.c
+++ b/gcc/lto/lto-lang.c
@@ -1137,13 +1137,6 @@ lto_init (void)
   /* Create the basic integer types.  */
   build_common_tree_nodes (flag_signed_char, /*short_double=*/false);
 
-  /* The global tree for the main identifier is filled in by
-     language-specific front-end initialization that is not run in the
-     LTO back-end.  It appears that all languages that perform such
-     initialization currently do so in the same way, so we do it here.  */
-  if (main_identifier_node == NULL_TREE)
-    main_identifier_node = get_identifier ("main");
-
   /* In the C++ front-end, fileptr_type_node is defined as a variant
      copy of of ptr_type_node, rather than ptr_node itself.  The
      distinction should only be relevant to the front-end, so we
diff --git a/gcc/predict.c b/gcc/predict.c
index c12b45f..819e64c 100644
--- a/gcc/predict.c
+++ b/gcc/predict.c
@@ -2275,7 +2275,7 @@ compute_function_frequency (void)
   basic_block bb;
   struct cgraph_node *node = cgraph_get_node (current_function_decl);
   if (DECL_STATIC_CONSTRUCTOR (current_function_decl)
-      || MAIN_NAME_P (DECL_NAME (current_function_decl)))
+      || cgraph_main_function_p (node))
     node->only_called_at_startup = true;
   if (DECL_STATIC_DESTRUCTOR (current_function_decl))
     node->only_called_at_exit = true;
@@ -2291,7 +2291,7 @@ compute_function_frequency (void)
         node->frequency = NODE_FREQUENCY_HOT;
       else if (flags & ECF_NORETURN)
         node->frequency = NODE_FREQUENCY_EXECUTED_ONCE;
-      else if (MAIN_NAME_P (DECL_NAME (current_function_decl)))
+      else if (cgraph_main_function_p (node))
         node->frequency = NODE_FREQUENCY_EXECUTED_ONCE;
       else if (DECL_STATIC_CONSTRUCTOR (current_function_decl)
 	       || DECL_STATIC_DESTRUCTOR (current_function_decl))
diff --git a/gcc/tree-ssa-structalias.c b/gcc/tree-ssa-structalias.c
index b65f5aa..9cb7a16 100644
--- a/gcc/tree-ssa-structalias.c
+++ b/gcc/tree-ssa-structalias.c
@@ -6933,7 +6933,7 @@ ipa_pta_execute (void)
 
 	  /* We also need to make function return values escape.  Nothing
 	     escapes by returning from main though.  */
-	  if (!MAIN_NAME_P (DECL_NAME (node->decl)))
+	  if (!cgraph_main_function_p (node->decl))
 	    {
 	      varinfo_t fi, rvi;
 	      fi = lookup_vi_for_tree (node->decl);
diff --git a/gcc/tree.c b/gcc/tree.c
index cfea9f7..d3bbeb0 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -9477,6 +9477,8 @@ build_common_tree_nodes (bool signed_char, bool short_double)
 
     va_list_type_node = t;
   }
+
+  main_identifier_node = get_identifier ("main");
 }
 
 /* A subroutine of build_common_builtin_nodes.  Define a builtin function.  */

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Richard Guenther]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 13265 bytes --]

On Tue, 20 Mar 2012, Tristan Gingold wrote:

> 
> On Mar 15, 2012, at 10:37 AM, Richard Guenther wrote:
> 
> > On Wed, 14 Mar 2012, Tristan Gingold wrote:
> [Â…]
> 
> > 
> > Well.  To make this work in LTO the "main" function (thus, the program
> > entry point) should be marked at cgraph level and all users of
> > MAIN_NAME_P should instead check a flag on the cgraph node.
> > 
> >> Will write a predicate in tree.[ch].
> > 
> > Please instead transition "main-ness" to the graph.
> 
> Hi,
> 
> here is the patch I wrote.  Does it match what you had in mind ?

Basically yes.  Comments below.

> main_identifier_node is now set in tree.c

Looks good, hopefully my review-grep was as good as yours ;)

> I haven't changed MAIN_NAME_P uses in c-decl.c and cp/decl.c (obviously).
> I haven't yet checked beyond simple build.
> 
> Tristan.
> 
> diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
> index 89f5438..c575e97 100644
> --- a/gcc/ada/gcc-interface/trans.c
> +++ b/gcc/ada/gcc-interface/trans.c
> @@ -622,8 +622,6 @@ gigi (Node_Id gnat_root, int max_gnat_node, int number_name ATTRIBUTE_UNUSED,
>  		       integer_type_node, NULL_TREE, true, false, true, false,
>  		       NULL, Empty);
>  
> -  main_identifier_node = get_identifier ("main");
> -
>    /* Install the builtins we might need, either internally or as
>       user available facilities for Intrinsic imports.  */
>    gnat_install_builtins ();
> diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
> index b83f45b..5d05d8a 100644
> --- a/gcc/c-family/c-common.c
> +++ b/gcc/c-family/c-common.c
> @@ -5094,8 +5094,6 @@ c_common_nodes_and_builtins (void)
>    if (!flag_preprocess_only)
>      c_define_builtins (va_list_ref_type_node, va_list_arg_type_node);
>  
> -  main_identifier_node = get_identifier ("main");
> -
>    /* Create the built-in __null node.  It is important that this is
>       not shared.  */
>    null_node = make_node (INTEGER_CST);
> diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
> index bd21169..7a7a774 100644
> --- a/gcc/cfgexpand.c
> +++ b/gcc/cfgexpand.c
> @@ -4513,9 +4513,8 @@ gimple_expand_cfg (void)
>  
>    /* If this function is `main', emit a call to `__main'
>       to run global initializers, etc.  */
> -  if (DECL_NAME (current_function_decl)
> -      && MAIN_NAME_P (DECL_NAME (current_function_decl))
> -      && DECL_FILE_SCOPE_P (current_function_decl))
> +  if (DECL_FILE_SCOPE_P (current_function_decl)
> +      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
>      expand_main_function ();

The DECL_FILE_SCOPE_P check is redundant, please remove them everywhere
you call cgraph_main_function_p.  I suppose returning false if the
cgraph node is NULL in cgraph_main_function_p would be good.

>  
>    /* Initialize the stack_protect_guard field.  This must happen after the
> diff --git a/gcc/cgraph.c b/gcc/cgraph.c
> index 9cc3690..528fd19 100644
> --- a/gcc/cgraph.c
> +++ b/gcc/cgraph.c
> @@ -2766,7 +2766,7 @@ cgraph_propagate_frequency_1 (struct cgraph_node *node, void *data)
>  	  /* It makes sense to put main() together with the static constructors.
>  	     It will be executed for sure, but rest of functions called from
>  	     main are definitely not at startup only.  */
> -	  if (MAIN_NAME_P (DECL_NAME (edge->caller->decl)))
> +	  if (cgraph_main_function_p (edge->caller))
>  	    d->only_called_at_startup = 0;
>            d->only_called_at_exit &= edge->caller->only_called_at_exit;
>  	}
> diff --git a/gcc/cgraph.h b/gcc/cgraph.h
> index 191364c..4db3417 100644
> --- a/gcc/cgraph.h
> +++ b/gcc/cgraph.h
> @@ -101,6 +101,9 @@ struct GTY(()) cgraph_local_info {
>  
>    /* True if the function may enter serial irrevocable mode.  */
>    unsigned tm_may_enter_irr : 1;
> +
> +  /* True if the function is the program entry point (main in C).  */
> +  unsigned main_function : 1;
>  };
>  
>  /* Information about the function that needs to be computed globally
> @@ -790,6 +793,13 @@ cgraph_next_function_with_gimple_body (struct cgraph_node *node)
>    return NULL;
>  }
>  
> +/* Return true iff NODE is the main function (main in C).  */
> +static inline bool
> +cgraph_main_function_p (struct cgraph_node *node)
> +{
> +  return node->local.main_function;

node && node->local.main_function

> +}
> +
>  /* Walk all functions with body defined.  */
>  #define FOR_EACH_FUNCTION_WITH_GIMPLE_BODY(node) \
>     for ((node) = cgraph_first_function_with_gimple_body (); (node); \
> diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
> index 516f187..4a59f63 100644
> --- a/gcc/cgraphunit.c
> +++ b/gcc/cgraphunit.c
> @@ -346,6 +346,10 @@ cgraph_finalize_function (tree decl, bool nested)
>    notice_global_symbol (decl);
>    node->local.finalized = true;
>    node->lowered = DECL_STRUCT_FUNCTION (decl)->cfg != NULL;
> +  node->local.main_function =
> +    DECL_FILE_SCOPE_P (decl)
> +    && ((!DECL_ASSEMBLER_NAME_SET_P (decl) && MAIN_NAME_P (DECL_NAME (decl)))
> +	|| decl_assembler_name_equal (decl, main_identifier_node));

If we finalize a function we should always create an assembler name,
thus I'd change the above to

  node->local.main_function = decl_assembler_name_equal (decl, 
main_identifier_node);

btw, decl_assembler_name_equal doesn't seem to remove target-specific
mangling - do some OSes "mangle" main differently (I'm thinking of
leading underscores or complete renames)?  Thus, I guess the
targets might want to be able to provide the main_identifier_assember_name
you use here.

>    if (cgraph_decide_is_function_needed (node, decl))
>      cgraph_mark_needed_node (node);
> diff --git a/gcc/config/i386/cygming.h b/gcc/config/i386/cygming.h
> index 2eccda9..8ac169e 100644
> --- a/gcc/config/i386/cygming.h
> +++ b/gcc/config/i386/cygming.h
> @@ -360,7 +360,8 @@ do {						\
>  
>  #undef PROFILE_HOOK
>  #define PROFILE_HOOK(LABEL)						\
> -  if (MAIN_NAME_P (DECL_NAME (current_function_decl)))			\
> +  if (DECL_FILE_SCOPE_P (current_function_decl)				\
> +      && cgraph_main_function_p (cgraph_get_node (current_function_decl))) \
>      {

See above.
									\
>        emit_call_insn (gen_rtx_CALL (VOIDmode,				\
>  	gen_rtx_MEM (FUNCTION_MODE,					\
> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> index 78a366e..5a3a712 100644
> --- a/gcc/config/i386/i386.c
> +++ b/gcc/config/i386/i386.c
> @@ -9509,9 +9509,8 @@ ix86_minimum_incoming_stack_boundary (bool sibcall)
>    /* Stack at entrance of main is aligned by runtime.  We use the
>       smallest incoming stack boundary. */
>    if (incoming_stack_boundary > MAIN_STACK_BOUNDARY
> -      && DECL_NAME (current_function_decl)
> -      && MAIN_NAME_P (DECL_NAME (current_function_decl))
> -      && DECL_FILE_SCOPE_P (current_function_decl))
> +      && DECL_FILE_SCOPE_P (current_function_decl)
> +      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
>      incoming_stack_boundary = MAIN_STACK_BOUNDARY;

Likewise.

>    return incoming_stack_boundary;
> diff --git a/gcc/config/pdp11/pdp11.c b/gcc/config/pdp11/pdp11.c
> index 42e3af0..aa38903 100644
> --- a/gcc/config/pdp11/pdp11.c
> +++ b/gcc/config/pdp11/pdp11.c
> @@ -240,7 +240,9 @@ pdp11_expand_prologue (void)
>  
>    /* If we are outputting code for main, the switch FPU to the
>       right mode if TARGET_FPU.  */
> -  if (MAIN_NAME_P (DECL_NAME (current_function_decl)) && TARGET_FPU)
> +  if (TARGET_FPU
> +      && DECL_FILE_SCOPE_P (current_function_decl)
> +      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
>      {

Likewise.

The rest looks good to me.  Honza?

Thanks,
Richard.

>        emit_insn (gen_setd ());
>        emit_insn (gen_seti ());
> diff --git a/gcc/fortran/trans-decl.c b/gcc/fortran/trans-decl.c
> index 8a1dd2e..6a1a494 100644
> --- a/gcc/fortran/trans-decl.c
> +++ b/gcc/fortran/trans-decl.c
> @@ -4922,7 +4922,6 @@ create_main_function (tree fndecl)
>    tmp =  build_function_type_list (integer_type_node, integer_type_node,
>  				   build_pointer_type (pchar_type_node),
>  				   NULL_TREE);
> -  main_identifier_node = get_identifier ("main");
>    ftn_main = build_decl (input_location, FUNCTION_DECL,
>        			 main_identifier_node, tmp);
>    DECL_EXTERNAL (ftn_main) = 0;
> diff --git a/gcc/ipa-split.c b/gcc/ipa-split.c
> index 9dddf39..595330e 100644
> --- a/gcc/ipa-split.c
> +++ b/gcc/ipa-split.c
> @@ -1409,7 +1409,7 @@ execute_split_functions (void)
>  	fprintf (dump_file, "Not splitting: noreturn/malloc function.\n");
>        return 0;
>      }
> -  if (MAIN_NAME_P (DECL_NAME (current_function_decl)))
> +  if (cgraph_main_function_p (node))
>      {
>        if (dump_file)
>  	fprintf (dump_file, "Not splitting: main function.\n");
> diff --git a/gcc/ipa.c b/gcc/ipa.c
> index 388291a..f9dc42d 100644
> --- a/gcc/ipa.c
> +++ b/gcc/ipa.c
> @@ -639,7 +639,7 @@ cgraph_externally_visible_p (struct cgraph_node *node,
>    else if (!whole_program)
>      return true;
>  
> -  if (MAIN_NAME_P (DECL_NAME (node->decl)))
> +  if (cgraph_main_function_p (node))
>      return true;
>  
>    return false;
> diff --git a/gcc/lto-cgraph.c b/gcc/lto-cgraph.c
> index 5e899bc..34bcc55 100644
> --- a/gcc/lto-cgraph.c
> +++ b/gcc/lto-cgraph.c
> @@ -502,6 +502,7 @@ lto_output_node (struct lto_simple_output_block *ob, struct cgraph_node *node,
>    bp_pack_value (&bp, node->local.versionable, 1);
>    bp_pack_value (&bp, node->local.can_change_signature, 1);
>    bp_pack_value (&bp, node->local.redefined_extern_inline, 1);
> +  bp_pack_value (&bp, node->local.main_function, 1);
>    bp_pack_value (&bp, node->needed, 1);
>    bp_pack_value (&bp, node->address_taken, 1);
>    bp_pack_value (&bp, node->abstract_and_needed, 1);
> @@ -904,6 +905,7 @@ input_overwrite_node (struct lto_file_decl_data *file_data,
>    node->local.versionable = bp_unpack_value (bp, 1);
>    node->local.can_change_signature = bp_unpack_value (bp, 1);
>    node->local.redefined_extern_inline = bp_unpack_value (bp, 1);
> +  node->local.main_function = bp_unpack_value (bp, 1);
>    node->needed = bp_unpack_value (bp, 1);
>    node->address_taken = bp_unpack_value (bp, 1);
>    node->abstract_and_needed = bp_unpack_value (bp, 1);
> diff --git a/gcc/lto/lto-lang.c b/gcc/lto/lto-lang.c
> index 999db8b..a44a35f 100644
> --- a/gcc/lto/lto-lang.c
> +++ b/gcc/lto/lto-lang.c
> @@ -1137,13 +1137,6 @@ lto_init (void)
>    /* Create the basic integer types.  */
>    build_common_tree_nodes (flag_signed_char, /*short_double=*/false);
>  
> -  /* The global tree for the main identifier is filled in by
> -     language-specific front-end initialization that is not run in the
> -     LTO back-end.  It appears that all languages that perform such
> -     initialization currently do so in the same way, so we do it here.  */
> -  if (main_identifier_node == NULL_TREE)
> -    main_identifier_node = get_identifier ("main");
> -
>    /* In the C++ front-end, fileptr_type_node is defined as a variant
>       copy of of ptr_type_node, rather than ptr_node itself.  The
>       distinction should only be relevant to the front-end, so we
> diff --git a/gcc/predict.c b/gcc/predict.c
> index c12b45f..819e64c 100644
> --- a/gcc/predict.c
> +++ b/gcc/predict.c
> @@ -2275,7 +2275,7 @@ compute_function_frequency (void)
>    basic_block bb;
>    struct cgraph_node *node = cgraph_get_node (current_function_decl);
>    if (DECL_STATIC_CONSTRUCTOR (current_function_decl)
> -      || MAIN_NAME_P (DECL_NAME (current_function_decl)))
> +      || cgraph_main_function_p (node))
>      node->only_called_at_startup = true;
>    if (DECL_STATIC_DESTRUCTOR (current_function_decl))
>      node->only_called_at_exit = true;
> @@ -2291,7 +2291,7 @@ compute_function_frequency (void)
>          node->frequency = NODE_FREQUENCY_HOT;
>        else if (flags & ECF_NORETURN)
>          node->frequency = NODE_FREQUENCY_EXECUTED_ONCE;
> -      else if (MAIN_NAME_P (DECL_NAME (current_function_decl)))
> +      else if (cgraph_main_function_p (node))
>          node->frequency = NODE_FREQUENCY_EXECUTED_ONCE;
>        else if (DECL_STATIC_CONSTRUCTOR (current_function_decl)
>  	       || DECL_STATIC_DESTRUCTOR (current_function_decl))
> diff --git a/gcc/tree-ssa-structalias.c b/gcc/tree-ssa-structalias.c
> index b65f5aa..9cb7a16 100644
> --- a/gcc/tree-ssa-structalias.c
> +++ b/gcc/tree-ssa-structalias.c
> @@ -6933,7 +6933,7 @@ ipa_pta_execute (void)
>  
>  	  /* We also need to make function return values escape.  Nothing
>  	     escapes by returning from main though.  */
> -	  if (!MAIN_NAME_P (DECL_NAME (node->decl)))
> +	  if (!cgraph_main_function_p (node->decl))
>  	    {
>  	      varinfo_t fi, rvi;
>  	      fi = lookup_vi_for_tree (node->decl);
> diff --git a/gcc/tree.c b/gcc/tree.c
> index cfea9f7..d3bbeb0 100644
> --- a/gcc/tree.c
> +++ b/gcc/tree.c
> @@ -9477,6 +9477,8 @@ build_common_tree_nodes (bool signed_char, bool short_double)
>  
>      va_list_type_node = t;
>    }
> +
> +  main_identifier_node = get_identifier ("main");
>  }
>  
>  /* A subroutine of build_common_builtin_nodes.  Define a builtin function.  */
> 
> 

-- 
Richard Guenther <rguenther@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Tristan Gingold]

On Mar 20, 2012, at 1:21 PM, Richard Guenther wrote:

> On Tue, 20 Mar 2012, Tristan Gingold wrote:
> 
>> 
>> On Mar 15, 2012, at 10:37 AM, Richard Guenther wrote:
>> 
>>> On Wed, 14 Mar 2012, Tristan Gingold wrote:
>> […]
>> 
>>> 
>>> Well.  To make this work in LTO the "main" function (thus, the program
>>> entry point) should be marked at cgraph level and all users of
>>> MAIN_NAME_P should instead check a flag on the cgraph node.
>>> 
>>>> Will write a predicate in tree.[ch].
>>> 
>>> Please instead transition "main-ness" to the graph.
>> 
>> Hi,
>> 
>> here is the patch I wrote.  Does it match what you had in mind ?
> 
> Basically yes.  Comments below.
> 
>> main_identifier_node is now set in tree.c
> 
> Looks good, hopefully my review-grep was as good as yours ;)

[…]

>> diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
>> index bd21169..7a7a774 100644
>> --- a/gcc/cfgexpand.c
>> +++ b/gcc/cfgexpand.c
>> @@ -4513,9 +4513,8 @@ gimple_expand_cfg (void)
>> 
>>   /* If this function is `main', emit a call to `__main'
>>      to run global initializers, etc.  */
>> -  if (DECL_NAME (current_function_decl)
>> -      && MAIN_NAME_P (DECL_NAME (current_function_decl))
>> -      && DECL_FILE_SCOPE_P (current_function_decl))
>> +  if (DECL_FILE_SCOPE_P (current_function_decl)
>> +      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
>>     expand_main_function ();
> 
> The DECL_FILE_SCOPE_P check is redundant, please remove them everywhere
> you call cgraph_main_function_p.  I suppose returning false if the
> cgraph node is NULL in cgraph_main_function_p would be good.

Ok.  (I added the DECL_FILE_SCOPE_P check to avoid the cgraph lookup for speed reason)

[…]

>> diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
>> index 516f187..4a59f63 100644
>> --- a/gcc/cgraphunit.c
>> +++ b/gcc/cgraphunit.c
>> @@ -346,6 +346,10 @@ cgraph_finalize_function (tree decl, bool nested)
>>   notice_global_symbol (decl);
>>   node->local.finalized = true;
>>   node->lowered = DECL_STRUCT_FUNCTION (decl)->cfg != NULL;
>> +  node->local.main_function =
>> +    DECL_FILE_SCOPE_P (decl)
>> +    && ((!DECL_ASSEMBLER_NAME_SET_P (decl) && MAIN_NAME_P (DECL_NAME (decl)))
>> +	|| decl_assembler_name_equal (decl, main_identifier_node));
> 
> If we finalize a function we should always create an assembler name,
> thus I'd change the above to
> 
>  node->local.main_function = decl_assembler_name_equal (decl, 
> main_identifier_node);

Indeed.  At worst, the assembler name is created during the call to notice_global_symbol.

> btw, decl_assembler_name_equal doesn't seem to remove target-specific
> mangling - do some OSes "mangle" main differently (I'm thinking of
> leading underscores or complete renames)?  Thus, I guess the
> targets might want to be able to provide the main_identifier_assember_name
> you use here.

I think this is currently OK because decl_assembler_name_equal deals
with leading underscore correctly.  I have checked that on Darwin,
which has a leading underscore.

The only target that mangle names is i386 cygwin/mingw, which 'annotates'
stdcall and fastcall function, but main() is regular.

But I agree this mechanism is fragile.

In order to make this mechanism stronger, we could add main_function_node, which
designates the FUNCTION_DECL that is the main function (if not NULL_TREE), with
a fallback on main_identifier_node for regular languages such as C or C++.

Tristan.

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Richard Guenther]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 4068 bytes --]

On Tue, 20 Mar 2012, Tristan Gingold wrote:

> 
> On Mar 20, 2012, at 1:21 PM, Richard Guenther wrote:
> 
> > On Tue, 20 Mar 2012, Tristan Gingold wrote:
> > 
> >> 
> >> On Mar 15, 2012, at 10:37 AM, Richard Guenther wrote:
> >> 
> >>> On Wed, 14 Mar 2012, Tristan Gingold wrote:
> >> [Â…]
> >> 
> >>> 
> >>> Well.  To make this work in LTO the "main" function (thus, the program
> >>> entry point) should be marked at cgraph level and all users of
> >>> MAIN_NAME_P should instead check a flag on the cgraph node.
> >>> 
> >>>> Will write a predicate in tree.[ch].
> >>> 
> >>> Please instead transition "main-ness" to the graph.
> >> 
> >> Hi,
> >> 
> >> here is the patch I wrote.  Does it match what you had in mind ?
> > 
> > Basically yes.  Comments below.
> > 
> >> main_identifier_node is now set in tree.c
> > 
> > Looks good, hopefully my review-grep was as good as yours ;)
> 
> [Â…]
> 
> >> diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
> >> index bd21169..7a7a774 100644
> >> --- a/gcc/cfgexpand.c
> >> +++ b/gcc/cfgexpand.c
> >> @@ -4513,9 +4513,8 @@ gimple_expand_cfg (void)
> >> 
> >>   /* If this function is `main', emit a call to `__main'
> >>      to run global initializers, etc.  */
> >> -  if (DECL_NAME (current_function_decl)
> >> -      && MAIN_NAME_P (DECL_NAME (current_function_decl))
> >> -      && DECL_FILE_SCOPE_P (current_function_decl))
> >> +  if (DECL_FILE_SCOPE_P (current_function_decl)
> >> +      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
> >>     expand_main_function ();
> > 
> > The DECL_FILE_SCOPE_P check is redundant, please remove them everywhere
> > you call cgraph_main_function_p.  I suppose returning false if the
> > cgraph node is NULL in cgraph_main_function_p would be good.
> 
> Ok.  (I added the DECL_FILE_SCOPE_P check to avoid the cgraph lookup for speed reason)
> 
> [Â…]
> 
> >> diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
> >> index 516f187..4a59f63 100644
> >> --- a/gcc/cgraphunit.c
> >> +++ b/gcc/cgraphunit.c
> >> @@ -346,6 +346,10 @@ cgraph_finalize_function (tree decl, bool nested)
> >>   notice_global_symbol (decl);
> >>   node->local.finalized = true;
> >>   node->lowered = DECL_STRUCT_FUNCTION (decl)->cfg != NULL;
> >> +  node->local.main_function =
> >> +    DECL_FILE_SCOPE_P (decl)
> >> +    && ((!DECL_ASSEMBLER_NAME_SET_P (decl) && MAIN_NAME_P (DECL_NAME (decl)))
> >> +	|| decl_assembler_name_equal (decl, main_identifier_node));
> > 
> > If we finalize a function we should always create an assembler name,
> > thus I'd change the above to
> > 
> >  node->local.main_function = decl_assembler_name_equal (decl, 
> > main_identifier_node);
> 
> Indeed.  At worst, the assembler name is created during the call to notice_global_symbol.
> 
> > btw, decl_assembler_name_equal doesn't seem to remove target-specific
> > mangling - do some OSes "mangle" main differently (I'm thinking of
> > leading underscores or complete renames)?  Thus, I guess the
> > targets might want to be able to provide the main_identifier_assember_name
> > you use here.
> 
> I think this is currently OK because decl_assembler_name_equal deals
> with leading underscore correctly.  I have checked that on Darwin,
> which has a leading underscore.
> 
> The only target that mangle names is i386 cygwin/mingw, which 'annotates'
> stdcall and fastcall function, but main() is regular.
> 
> But I agree this mechanism is fragile.
> 
> In order to make this mechanism stronger, we could add main_function_node, which
> designates the FUNCTION_DECL that is the main function (if not NULL_TREE), with
> a fallback on main_identifier_node for regular languages such as C or C++.

I'd rather get away from using a global main_identifier_node, instead
make that frontend specific, and introduce targetm.main_assembler_name
which the assembler-name creating langhook would make sure to use
when mangling what the FE thinks main is.  main_identifier_node should
not serve any purpose outside of Frontends.

But I see both as a possible cleanup opportunity, not a necessary change.

Richard.

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Tristan Gingold]

On Mar 20, 2012, at 3:19 PM, Richard Guenther wrote:

[…]
> 
> I'd rather get away from using a global main_identifier_node, instead
> make that frontend specific, and introduce targetm.main_assembler_name
> which the assembler-name creating langhook would make sure to use
> when mangling what the FE thinks main is.  main_identifier_node should
> not serve any purpose outside of Frontends.
> 
> But I see both as a possible cleanup opportunity, not a necessary change.

Something along these lines ?

Tristan.

diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
index 89f5438..c575e97 100644
--- a/gcc/ada/gcc-interface/trans.c
+++ b/gcc/ada/gcc-interface/trans.c
@@ -622,8 +622,6 @@ gigi (Node_Id gnat_root, int max_gnat_node, int number_name ATTRIBUTE_UNUSED,
 		       integer_type_node, NULL_TREE, true, false, true, false,
 		       NULL, Empty);
 
-  main_identifier_node = get_identifier ("main");
-
   /* Install the builtins we might need, either internally or as
      user available facilities for Intrinsic imports.  */
   gnat_install_builtins ();
diff --git a/gcc/ada/gcc-interface/utils.c b/gcc/ada/gcc-interface/utils.c
index 7383358..b0fa085d 100644
--- a/gcc/ada/gcc-interface/utils.c
+++ b/gcc/ada/gcc-interface/utils.c
@@ -1902,14 +1902,12 @@ create_subprog_decl (tree subprog_name, tree asm_name, tree subprog_type,
     {
       SET_DECL_ASSEMBLER_NAME (subprog_decl, asm_name);
 
-      /* The expand_main_function circuitry expects "main_identifier_node" to
-	 designate the DECL_NAME of the 'main' entry point, in turn expected
-	 to be declared as the "main" function literally by default.  Ada
-	 program entry points are typically declared with a different name
+      /* Ada program entry points are typically declared with a different name
 	 within the binder generated file, exported as 'main' to satisfy the
-	 system expectations.  Force main_identifier_node in this case.  */
-      if (asm_name == main_identifier_node)
-	DECL_NAME (subprog_decl) = main_identifier_node;
+	 system expectations.  Force main_assembler_node in this case.  */
+      if (IDENTIFIER_LENGTH (asm_name) == 4
+	  && memcmp (IDENTIFIER_POINTER (asm_name), "main", 4) == 0)
+	DECL_NAME (subprog_decl) = main_assembler_name;
     }
 
   /* Add this decl to the current binding level.  */
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 835b13b..fea5181 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -291,6 +291,8 @@ enum c_tree_index
 
     CTI_DEFAULT_FUNCTION_TYPE,
 
+    CTI_MAIN_IDENTIFIER,
+
     /* These are not types, but we have to look them up all the time.  */
     CTI_FUNCTION_NAME_DECL,
     CTI_PRETTY_FUNCTION_NAME_DECL,
@@ -426,6 +428,10 @@ extern const unsigned int num_c_common_reswords;
 
 #define default_function_type		c_global_trees[CTI_DEFAULT_FUNCTION_TYPE]
 
+#define main_identifier_node		c_global_trees[CTI_MAIN_IDENTIFIER]
+#define MAIN_NAME_P(NODE) \
+  (IDENTIFIER_NODE_CHECK (NODE) == main_identifier_node)
+
 #define function_name_decl_node		c_global_trees[CTI_FUNCTION_NAME_DECL]
 #define pretty_function_name_decl_node	c_global_trees[CTI_PRETTY_FUNCTION_NAME_DECL]
 #define c99_function_name_decl_node		c_global_trees[CTI_C99_FUNCTION_NAME_DECL]
diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index bd21169..db53309 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -4513,9 +4513,7 @@ gimple_expand_cfg (void)
 
   /* If this function is `main', emit a call to `__main'
      to run global initializers, etc.  */
-  if (DECL_NAME (current_function_decl)
-      && MAIN_NAME_P (DECL_NAME (current_function_decl))
-      && DECL_FILE_SCOPE_P (current_function_decl))
+  if (cgraph_main_function_p (cgraph_get_node (current_function_decl)))
     expand_main_function ();
 
   /* Initialize the stack_protect_guard field.  This must happen after the
diff --git a/gcc/cgraph.c b/gcc/cgraph.c
index 9cc3690..528fd19 100644
--- a/gcc/cgraph.c
+++ b/gcc/cgraph.c
@@ -2766,7 +2766,7 @@ cgraph_propagate_frequency_1 (struct cgraph_node *node, void *data)
 	  /* It makes sense to put main() together with the static constructors.
 	     It will be executed for sure, but rest of functions called from
 	     main are definitely not at startup only.  */
-	  if (MAIN_NAME_P (DECL_NAME (edge->caller->decl)))
+	  if (cgraph_main_function_p (edge->caller))
 	    d->only_called_at_startup = 0;
           d->only_called_at_exit &= edge->caller->only_called_at_exit;
 	}
diff --git a/gcc/cgraph.h b/gcc/cgraph.h
index 191364c..089d851 100644
--- a/gcc/cgraph.h
+++ b/gcc/cgraph.h
@@ -101,6 +101,9 @@ struct GTY(()) cgraph_local_info {
 
   /* True if the function may enter serial irrevocable mode.  */
   unsigned tm_may_enter_irr : 1;
+
+  /* True if the function is the program entry point (main in C).  */
+  unsigned main_function : 1;
 };
 
 /* Information about the function that needs to be computed globally
@@ -790,6 +793,13 @@ cgraph_next_function_with_gimple_body (struct cgraph_node *node)
   return NULL;
 }
 
+/* Return true iff NODE is the main function (main in C).  */
+static inline bool
+cgraph_main_function_p (struct cgraph_node *node)
+{
+  return node && node->local.main_function;
+}
+
 /* Walk all functions with body defined.  */
 #define FOR_EACH_FUNCTION_WITH_GIMPLE_BODY(node) \
    for ((node) = cgraph_first_function_with_gimple_body (); (node); \
diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
index 516f187..556f21c 100644
--- a/gcc/cgraphunit.c
+++ b/gcc/cgraphunit.c
@@ -346,6 +346,9 @@ cgraph_finalize_function (tree decl, bool nested)
   notice_global_symbol (decl);
   node->local.finalized = true;
   node->lowered = DECL_STRUCT_FUNCTION (decl)->cfg != NULL;
+  node->local.main_function =
+    DECL_FILE_SCOPE_P (decl)
+    && decl_assembler_name_equal (decl, main_assembler_name);
 
   if (cgraph_decide_is_function_needed (node, decl))
     cgraph_mark_needed_node (node);
diff --git a/gcc/config/i386/cygming.h b/gcc/config/i386/cygming.h
index 2eccda9..e0f6234 100644
--- a/gcc/config/i386/cygming.h
+++ b/gcc/config/i386/cygming.h
@@ -360,7 +360,7 @@ do {						\
 
 #undef PROFILE_HOOK
 #define PROFILE_HOOK(LABEL)						\
-  if (MAIN_NAME_P (DECL_NAME (current_function_decl)))			\
+  if (cgraph_main_function_p (cgraph_get_node (current_function_decl))) \
     {									\
       emit_call_insn (gen_rtx_CALL (VOIDmode,				\
 	gen_rtx_MEM (FUNCTION_MODE,					\
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 78a366e..c4a78b1 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -9509,9 +9509,7 @@ ix86_minimum_incoming_stack_boundary (bool sibcall)
   /* Stack at entrance of main is aligned by runtime.  We use the
      smallest incoming stack boundary. */
   if (incoming_stack_boundary > MAIN_STACK_BOUNDARY
-      && DECL_NAME (current_function_decl)
-      && MAIN_NAME_P (DECL_NAME (current_function_decl))
-      && DECL_FILE_SCOPE_P (current_function_decl))
+      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
     incoming_stack_boundary = MAIN_STACK_BOUNDARY;
 
   return incoming_stack_boundary;
diff --git a/gcc/config/pdp11/pdp11.c b/gcc/config/pdp11/pdp11.c
index 42e3af0..d1df127 100644
--- a/gcc/config/pdp11/pdp11.c
+++ b/gcc/config/pdp11/pdp11.c
@@ -240,7 +240,8 @@ pdp11_expand_prologue (void)
 
   /* If we are outputting code for main, the switch FPU to the
      right mode if TARGET_FPU.  */
-  if (MAIN_NAME_P (DECL_NAME (current_function_decl)) && TARGET_FPU)
+  if (TARGET_FPU
+      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
     {
       emit_insn (gen_setd ());
       emit_insn (gen_seti ());
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 2891bb6..654f8ec 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -8102,6 +8102,11 @@ systems.  This macro is used in @code{assemble_name}.
 Given a symbol @var{name}, perform same mangling as @code{varasm.c}'s @code{assemble_name}, but in memory rather than to a file stream, returning result as an @code{IDENTIFIER_NODE}.  Required for correct LTO symtabs.  The default implementation calls the @code{TARGET_STRIP_NAME_ENCODING} hook and then prepends the @code{USER_LABEL_PREFIX}, if any.
 @end deftypefn
 
+@deftypefn {Target Hook} tree TARGET_MAIN_ASSEMBLER_NAME (void)
+It returns the assembler name for the 'main' function.
+The default is to return 'main', which will be prefixed by USER_LABEL_PREFIX.
+@end deftypefn
+
 @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
 A C statement (sans semicolon) to output a reference to
 @code{SYMBOL_REF} @var{sym}.  If not defined, @code{assemble_name}
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index a222654..6765344 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -8007,6 +8007,8 @@ systems.  This macro is used in @code{assemble_name}.
 
 @hook TARGET_MANGLE_ASSEMBLER_NAME
 
+@hook TARGET_MAIN_ASSEMBLER_NAME
+
 @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
 A C statement (sans semicolon) to output a reference to
 @code{SYMBOL_REF} @var{sym}.  If not defined, @code{assemble_name}
diff --git a/gcc/fortran/trans-decl.c b/gcc/fortran/trans-decl.c
index 8a1dd2e..a51b0ac 100644
--- a/gcc/fortran/trans-decl.c
+++ b/gcc/fortran/trans-decl.c
@@ -4922,9 +4922,8 @@ create_main_function (tree fndecl)
   tmp =  build_function_type_list (integer_type_node, integer_type_node,
 				   build_pointer_type (pchar_type_node),
 				   NULL_TREE);
-  main_identifier_node = get_identifier ("main");
   ftn_main = build_decl (input_location, FUNCTION_DECL,
-      			 main_identifier_node, tmp);
+			 get_identifier ("main"), tmp);
   DECL_EXTERNAL (ftn_main) = 0;
   TREE_PUBLIC (ftn_main) = 1;
   TREE_STATIC (ftn_main) = 1;
diff --git a/gcc/ipa-split.c b/gcc/ipa-split.c
index 9dddf39..595330e 100644
--- a/gcc/ipa-split.c
+++ b/gcc/ipa-split.c
@@ -1409,7 +1409,7 @@ execute_split_functions (void)
 	fprintf (dump_file, "Not splitting: noreturn/malloc function.\n");
       return 0;
     }
-  if (MAIN_NAME_P (DECL_NAME (current_function_decl)))
+  if (cgraph_main_function_p (node))
     {
       if (dump_file)
 	fprintf (dump_file, "Not splitting: main function.\n");
diff --git a/gcc/ipa.c b/gcc/ipa.c
index 388291a..f9dc42d 100644
--- a/gcc/ipa.c
+++ b/gcc/ipa.c
@@ -639,7 +639,7 @@ cgraph_externally_visible_p (struct cgraph_node *node,
   else if (!whole_program)
     return true;
 
-  if (MAIN_NAME_P (DECL_NAME (node->decl)))
+  if (cgraph_main_function_p (node))
     return true;
 
   return false;
diff --git a/gcc/lto-cgraph.c b/gcc/lto-cgraph.c
index 5e899bc..34bcc55 100644
--- a/gcc/lto-cgraph.c
+++ b/gcc/lto-cgraph.c
@@ -502,6 +502,7 @@ lto_output_node (struct lto_simple_output_block *ob, struct cgraph_node *node,
   bp_pack_value (&bp, node->local.versionable, 1);
   bp_pack_value (&bp, node->local.can_change_signature, 1);
   bp_pack_value (&bp, node->local.redefined_extern_inline, 1);
+  bp_pack_value (&bp, node->local.main_function, 1);
   bp_pack_value (&bp, node->needed, 1);
   bp_pack_value (&bp, node->address_taken, 1);
   bp_pack_value (&bp, node->abstract_and_needed, 1);
@@ -904,6 +905,7 @@ input_overwrite_node (struct lto_file_decl_data *file_data,
   node->local.versionable = bp_unpack_value (bp, 1);
   node->local.can_change_signature = bp_unpack_value (bp, 1);
   node->local.redefined_extern_inline = bp_unpack_value (bp, 1);
+  node->local.main_function = bp_unpack_value (bp, 1);
   node->needed = bp_unpack_value (bp, 1);
   node->address_taken = bp_unpack_value (bp, 1);
   node->abstract_and_needed = bp_unpack_value (bp, 1);
diff --git a/gcc/lto/lto-lang.c b/gcc/lto/lto-lang.c
index 999db8b..a44a35f 100644
--- a/gcc/lto/lto-lang.c
+++ b/gcc/lto/lto-lang.c
@@ -1137,13 +1137,6 @@ lto_init (void)
   /* Create the basic integer types.  */
   build_common_tree_nodes (flag_signed_char, /*short_double=*/false);
 
-  /* The global tree for the main identifier is filled in by
-     language-specific front-end initialization that is not run in the
-     LTO back-end.  It appears that all languages that perform such
-     initialization currently do so in the same way, so we do it here.  */
-  if (main_identifier_node == NULL_TREE)
-    main_identifier_node = get_identifier ("main");
-
   /* In the C++ front-end, fileptr_type_node is defined as a variant
      copy of of ptr_type_node, rather than ptr_node itself.  The
      distinction should only be relevant to the front-end, so we
diff --git a/gcc/predict.c b/gcc/predict.c
index c12b45f..819e64c 100644
--- a/gcc/predict.c
+++ b/gcc/predict.c
@@ -2275,7 +2275,7 @@ compute_function_frequency (void)
   basic_block bb;
   struct cgraph_node *node = cgraph_get_node (current_function_decl);
   if (DECL_STATIC_CONSTRUCTOR (current_function_decl)
-      || MAIN_NAME_P (DECL_NAME (current_function_decl)))
+      || cgraph_main_function_p (node))
     node->only_called_at_startup = true;
   if (DECL_STATIC_DESTRUCTOR (current_function_decl))
     node->only_called_at_exit = true;
@@ -2291,7 +2291,7 @@ compute_function_frequency (void)
         node->frequency = NODE_FREQUENCY_HOT;
       else if (flags & ECF_NORETURN)
         node->frequency = NODE_FREQUENCY_EXECUTED_ONCE;
-      else if (MAIN_NAME_P (DECL_NAME (current_function_decl)))
+      else if (cgraph_main_function_p (node))
         node->frequency = NODE_FREQUENCY_EXECUTED_ONCE;
       else if (DECL_STATIC_CONSTRUCTOR (current_function_decl)
 	       || DECL_STATIC_DESTRUCTOR (current_function_decl))
diff --git a/gcc/target.def b/gcc/target.def
index d658b11..2c91620 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -1473,6 +1473,17 @@ DEFHOOK
  tree, (tree decl, tree  id),
  default_mangle_decl_assembler_name)
 
+/* Return the assembler name for the 'main' function.  It should return the
+   same identifier as mandle_decl_assembler_name will for the C 'main'
+   function.
+   The default is to return 'main'.  */
+DEFHOOK
+(main_assembler_name,
+ "It returns the assembler name for the 'main' function.\n\
+The default is to return 'main', which will be prefixed by USER_LABEL_PREFIX.",
+ tree, (void),
+ default_main_assembler_name)
+
 /* Do something target-specific to record properties of the DECL into
    the associated SYMBOL_REF.  */
 DEFHOOK
diff --git a/gcc/targhooks.c b/gcc/targhooks.c
index 8e3d74e..08535b4 100644
--- a/gcc/targhooks.c
+++ b/gcc/targhooks.c
@@ -371,6 +371,13 @@ default_mangle_assembler_name (const char *name ATTRIBUTE_UNUSED)
   return get_identifier (stripped);
 }
 
+/* The default implementation of TARGET_MAIN_ASSEMBLER_NAME.  */
+tree
+default_main_assembler_name (void)
+{
+  return get_identifier ("main");
+}
+
 /* True if MODE is valid for the target.  By "valid", we mean able to
    be manipulated in non-trivial ways.  In particular, this means all
    the arithmetic is supported.
diff --git a/gcc/targhooks.h b/gcc/targhooks.h
index 8618115..3016f04 100644
--- a/gcc/targhooks.h
+++ b/gcc/targhooks.h
@@ -66,6 +66,7 @@ extern void default_print_operand (FILE *, rtx, int);
 extern void default_print_operand_address (FILE *, rtx);
 extern bool default_print_operand_punct_valid_p (unsigned char);
 extern tree default_mangle_assembler_name (const char *);
+extern tree default_main_assembler_name (void);
 
 extern bool default_scalar_mode_supported_p (enum machine_mode);
 extern bool targhook_words_big_endian (void);
diff --git a/gcc/tree-ssa-structalias.c b/gcc/tree-ssa-structalias.c
index b65f5aa..9cb7a16 100644
--- a/gcc/tree-ssa-structalias.c
+++ b/gcc/tree-ssa-structalias.c
@@ -6933,7 +6933,7 @@ ipa_pta_execute (void)
 
 	  /* We also need to make function return values escape.  Nothing
 	     escapes by returning from main though.  */
-	  if (!MAIN_NAME_P (DECL_NAME (node->decl)))
+	  if (!cgraph_main_function_p (node->decl))
 	    {
 	      varinfo_t fi, rvi;
 	      fi = lookup_vi_for_tree (node->decl);
diff --git a/gcc/tree.c b/gcc/tree.c
index cfea9f7..6a0d380 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -9477,6 +9477,8 @@ build_common_tree_nodes (bool signed_char, bool short_double)
 
     va_list_type_node = t;
   }
+
+  main_assembler_name = targetm.main_assembler_name ();
 }
 
 /* A subroutine of build_common_builtin_nodes.  Define a builtin function.  */
diff --git a/gcc/tree.h b/gcc/tree.h
index 62ee454..45c750f 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -3805,7 +3805,7 @@ enum tree_index
 
   TI_VOID_LIST_NODE,
 
-  TI_MAIN_IDENTIFIER,
+  TI_MAIN_ASSEMBLER_NAME,
 
   TI_SAT_SFRACT_TYPE,
   TI_SAT_FRACT_TYPE,
@@ -4048,9 +4048,7 @@ extern GTY(()) tree global_trees[TI_MAX];
    anything else about this node.  */
 #define void_list_node                  global_trees[TI_VOID_LIST_NODE]
 
-#define main_identifier_node		global_trees[TI_MAIN_IDENTIFIER]
-#define MAIN_NAME_P(NODE) \
-  (IDENTIFIER_NODE_CHECK (NODE) == main_identifier_node)
+#define main_assembler_name		global_trees[TI_MAIN_ASSEMBLER_NAME]
 
 /* Optimization options (OPTIMIZATION_NODE) to use for default and current
    functions.  */

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Richard Guenther]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 18193 bytes --]

On Tue, 20 Mar 2012, Tristan Gingold wrote:

> 
> On Mar 20, 2012, at 3:19 PM, Richard Guenther wrote:
> 
> [Â…]
> > 
> > I'd rather get away from using a global main_identifier_node, instead
> > make that frontend specific, and introduce targetm.main_assembler_name
> > which the assembler-name creating langhook would make sure to use
> > when mangling what the FE thinks main is.  main_identifier_node should
> > not serve any purpose outside of Frontends.
> > 
> > But I see both as a possible cleanup opportunity, not a necessary change.
> 
> Something along these lines ?

Yes, but I'd simply call the hook at the places you now use
main_assembler_name and not create a global tree node for it.

Richard.

> Tristan.
> 
> diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
> index 89f5438..c575e97 100644
> --- a/gcc/ada/gcc-interface/trans.c
> +++ b/gcc/ada/gcc-interface/trans.c
> @@ -622,8 +622,6 @@ gigi (Node_Id gnat_root, int max_gnat_node, int number_name ATTRIBUTE_UNUSED,
>  		       integer_type_node, NULL_TREE, true, false, true, false,
>  		       NULL, Empty);
>  
> -  main_identifier_node = get_identifier ("main");
> -
>    /* Install the builtins we might need, either internally or as
>       user available facilities for Intrinsic imports.  */
>    gnat_install_builtins ();
> diff --git a/gcc/ada/gcc-interface/utils.c b/gcc/ada/gcc-interface/utils.c
> index 7383358..b0fa085d 100644
> --- a/gcc/ada/gcc-interface/utils.c
> +++ b/gcc/ada/gcc-interface/utils.c
> @@ -1902,14 +1902,12 @@ create_subprog_decl (tree subprog_name, tree asm_name, tree subprog_type,
>      {
>        SET_DECL_ASSEMBLER_NAME (subprog_decl, asm_name);
>  
> -      /* The expand_main_function circuitry expects "main_identifier_node" to
> -	 designate the DECL_NAME of the 'main' entry point, in turn expected
> -	 to be declared as the "main" function literally by default.  Ada
> -	 program entry points are typically declared with a different name
> +      /* Ada program entry points are typically declared with a different name
>  	 within the binder generated file, exported as 'main' to satisfy the
> -	 system expectations.  Force main_identifier_node in this case.  */
> -      if (asm_name == main_identifier_node)
> -	DECL_NAME (subprog_decl) = main_identifier_node;
> +	 system expectations.  Force main_assembler_node in this case.  */
> +      if (IDENTIFIER_LENGTH (asm_name) == 4
> +	  && memcmp (IDENTIFIER_POINTER (asm_name), "main", 4) == 0)
> +	DECL_NAME (subprog_decl) = main_assembler_name;
>      }
>  
>    /* Add this decl to the current binding level.  */
> diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
> index 835b13b..fea5181 100644
> --- a/gcc/c-family/c-common.h
> +++ b/gcc/c-family/c-common.h
> @@ -291,6 +291,8 @@ enum c_tree_index
>  
>      CTI_DEFAULT_FUNCTION_TYPE,
>  
> +    CTI_MAIN_IDENTIFIER,
> +
>      /* These are not types, but we have to look them up all the time.  */
>      CTI_FUNCTION_NAME_DECL,
>      CTI_PRETTY_FUNCTION_NAME_DECL,
> @@ -426,6 +428,10 @@ extern const unsigned int num_c_common_reswords;
>  
>  #define default_function_type		c_global_trees[CTI_DEFAULT_FUNCTION_TYPE]
>  
> +#define main_identifier_node		c_global_trees[CTI_MAIN_IDENTIFIER]
> +#define MAIN_NAME_P(NODE) \
> +  (IDENTIFIER_NODE_CHECK (NODE) == main_identifier_node)
> +
>  #define function_name_decl_node		c_global_trees[CTI_FUNCTION_NAME_DECL]
>  #define pretty_function_name_decl_node	c_global_trees[CTI_PRETTY_FUNCTION_NAME_DECL]
>  #define c99_function_name_decl_node		c_global_trees[CTI_C99_FUNCTION_NAME_DECL]
> diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
> index bd21169..db53309 100644
> --- a/gcc/cfgexpand.c
> +++ b/gcc/cfgexpand.c
> @@ -4513,9 +4513,7 @@ gimple_expand_cfg (void)
>  
>    /* If this function is `main', emit a call to `__main'
>       to run global initializers, etc.  */
> -  if (DECL_NAME (current_function_decl)
> -      && MAIN_NAME_P (DECL_NAME (current_function_decl))
> -      && DECL_FILE_SCOPE_P (current_function_decl))
> +  if (cgraph_main_function_p (cgraph_get_node (current_function_decl)))
>      expand_main_function ();
>  
>    /* Initialize the stack_protect_guard field.  This must happen after the
> diff --git a/gcc/cgraph.c b/gcc/cgraph.c
> index 9cc3690..528fd19 100644
> --- a/gcc/cgraph.c
> +++ b/gcc/cgraph.c
> @@ -2766,7 +2766,7 @@ cgraph_propagate_frequency_1 (struct cgraph_node *node, void *data)
>  	  /* It makes sense to put main() together with the static constructors.
>  	     It will be executed for sure, but rest of functions called from
>  	     main are definitely not at startup only.  */
> -	  if (MAIN_NAME_P (DECL_NAME (edge->caller->decl)))
> +	  if (cgraph_main_function_p (edge->caller))
>  	    d->only_called_at_startup = 0;
>            d->only_called_at_exit &= edge->caller->only_called_at_exit;
>  	}
> diff --git a/gcc/cgraph.h b/gcc/cgraph.h
> index 191364c..089d851 100644
> --- a/gcc/cgraph.h
> +++ b/gcc/cgraph.h
> @@ -101,6 +101,9 @@ struct GTY(()) cgraph_local_info {
>  
>    /* True if the function may enter serial irrevocable mode.  */
>    unsigned tm_may_enter_irr : 1;
> +
> +  /* True if the function is the program entry point (main in C).  */
> +  unsigned main_function : 1;
>  };
>  
>  /* Information about the function that needs to be computed globally
> @@ -790,6 +793,13 @@ cgraph_next_function_with_gimple_body (struct cgraph_node *node)
>    return NULL;
>  }
>  
> +/* Return true iff NODE is the main function (main in C).  */
> +static inline bool
> +cgraph_main_function_p (struct cgraph_node *node)
> +{
> +  return node && node->local.main_function;
> +}
> +
>  /* Walk all functions with body defined.  */
>  #define FOR_EACH_FUNCTION_WITH_GIMPLE_BODY(node) \
>     for ((node) = cgraph_first_function_with_gimple_body (); (node); \
> diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
> index 516f187..556f21c 100644
> --- a/gcc/cgraphunit.c
> +++ b/gcc/cgraphunit.c
> @@ -346,6 +346,9 @@ cgraph_finalize_function (tree decl, bool nested)
>    notice_global_symbol (decl);
>    node->local.finalized = true;
>    node->lowered = DECL_STRUCT_FUNCTION (decl)->cfg != NULL;
> +  node->local.main_function =
> +    DECL_FILE_SCOPE_P (decl)
> +    && decl_assembler_name_equal (decl, main_assembler_name);
>  
>    if (cgraph_decide_is_function_needed (node, decl))
>      cgraph_mark_needed_node (node);
> diff --git a/gcc/config/i386/cygming.h b/gcc/config/i386/cygming.h
> index 2eccda9..e0f6234 100644
> --- a/gcc/config/i386/cygming.h
> +++ b/gcc/config/i386/cygming.h
> @@ -360,7 +360,7 @@ do {						\
>  
>  #undef PROFILE_HOOK
>  #define PROFILE_HOOK(LABEL)						\
> -  if (MAIN_NAME_P (DECL_NAME (current_function_decl)))			\
> +  if (cgraph_main_function_p (cgraph_get_node (current_function_decl))) \
>      {									\
>        emit_call_insn (gen_rtx_CALL (VOIDmode,				\
>  	gen_rtx_MEM (FUNCTION_MODE,					\
> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> index 78a366e..c4a78b1 100644
> --- a/gcc/config/i386/i386.c
> +++ b/gcc/config/i386/i386.c
> @@ -9509,9 +9509,7 @@ ix86_minimum_incoming_stack_boundary (bool sibcall)
>    /* Stack at entrance of main is aligned by runtime.  We use the
>       smallest incoming stack boundary. */
>    if (incoming_stack_boundary > MAIN_STACK_BOUNDARY
> -      && DECL_NAME (current_function_decl)
> -      && MAIN_NAME_P (DECL_NAME (current_function_decl))
> -      && DECL_FILE_SCOPE_P (current_function_decl))
> +      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
>      incoming_stack_boundary = MAIN_STACK_BOUNDARY;
>  
>    return incoming_stack_boundary;
> diff --git a/gcc/config/pdp11/pdp11.c b/gcc/config/pdp11/pdp11.c
> index 42e3af0..d1df127 100644
> --- a/gcc/config/pdp11/pdp11.c
> +++ b/gcc/config/pdp11/pdp11.c
> @@ -240,7 +240,8 @@ pdp11_expand_prologue (void)
>  
>    /* If we are outputting code for main, the switch FPU to the
>       right mode if TARGET_FPU.  */
> -  if (MAIN_NAME_P (DECL_NAME (current_function_decl)) && TARGET_FPU)
> +  if (TARGET_FPU
> +      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
>      {
>        emit_insn (gen_setd ());
>        emit_insn (gen_seti ());
> diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
> index 2891bb6..654f8ec 100644
> --- a/gcc/doc/tm.texi
> +++ b/gcc/doc/tm.texi
> @@ -8102,6 +8102,11 @@ systems.  This macro is used in @code{assemble_name}.
>  Given a symbol @var{name}, perform same mangling as @code{varasm.c}'s @code{assemble_name}, but in memory rather than to a file stream, returning result as an @code{IDENTIFIER_NODE}.  Required for correct LTO symtabs.  The default implementation calls the @code{TARGET_STRIP_NAME_ENCODING} hook and then prepends the @code{USER_LABEL_PREFIX}, if any.
>  @end deftypefn
>  
> +@deftypefn {Target Hook} tree TARGET_MAIN_ASSEMBLER_NAME (void)
> +It returns the assembler name for the 'main' function.
> +The default is to return 'main', which will be prefixed by USER_LABEL_PREFIX.
> +@end deftypefn
> +
>  @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
>  A C statement (sans semicolon) to output a reference to
>  @code{SYMBOL_REF} @var{sym}.  If not defined, @code{assemble_name}
> diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
> index a222654..6765344 100644
> --- a/gcc/doc/tm.texi.in
> +++ b/gcc/doc/tm.texi.in
> @@ -8007,6 +8007,8 @@ systems.  This macro is used in @code{assemble_name}.
>  
>  @hook TARGET_MANGLE_ASSEMBLER_NAME
>  
> +@hook TARGET_MAIN_ASSEMBLER_NAME
> +
>  @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
>  A C statement (sans semicolon) to output a reference to
>  @code{SYMBOL_REF} @var{sym}.  If not defined, @code{assemble_name}
> diff --git a/gcc/fortran/trans-decl.c b/gcc/fortran/trans-decl.c
> index 8a1dd2e..a51b0ac 100644
> --- a/gcc/fortran/trans-decl.c
> +++ b/gcc/fortran/trans-decl.c
> @@ -4922,9 +4922,8 @@ create_main_function (tree fndecl)
>    tmp =  build_function_type_list (integer_type_node, integer_type_node,
>  				   build_pointer_type (pchar_type_node),
>  				   NULL_TREE);
> -  main_identifier_node = get_identifier ("main");
>    ftn_main = build_decl (input_location, FUNCTION_DECL,
> -      			 main_identifier_node, tmp);
> +			 get_identifier ("main"), tmp);
>    DECL_EXTERNAL (ftn_main) = 0;
>    TREE_PUBLIC (ftn_main) = 1;
>    TREE_STATIC (ftn_main) = 1;
> diff --git a/gcc/ipa-split.c b/gcc/ipa-split.c
> index 9dddf39..595330e 100644
> --- a/gcc/ipa-split.c
> +++ b/gcc/ipa-split.c
> @@ -1409,7 +1409,7 @@ execute_split_functions (void)
>  	fprintf (dump_file, "Not splitting: noreturn/malloc function.\n");
>        return 0;
>      }
> -  if (MAIN_NAME_P (DECL_NAME (current_function_decl)))
> +  if (cgraph_main_function_p (node))
>      {
>        if (dump_file)
>  	fprintf (dump_file, "Not splitting: main function.\n");
> diff --git a/gcc/ipa.c b/gcc/ipa.c
> index 388291a..f9dc42d 100644
> --- a/gcc/ipa.c
> +++ b/gcc/ipa.c
> @@ -639,7 +639,7 @@ cgraph_externally_visible_p (struct cgraph_node *node,
>    else if (!whole_program)
>      return true;
>  
> -  if (MAIN_NAME_P (DECL_NAME (node->decl)))
> +  if (cgraph_main_function_p (node))
>      return true;
>  
>    return false;
> diff --git a/gcc/lto-cgraph.c b/gcc/lto-cgraph.c
> index 5e899bc..34bcc55 100644
> --- a/gcc/lto-cgraph.c
> +++ b/gcc/lto-cgraph.c
> @@ -502,6 +502,7 @@ lto_output_node (struct lto_simple_output_block *ob, struct cgraph_node *node,
>    bp_pack_value (&bp, node->local.versionable, 1);
>    bp_pack_value (&bp, node->local.can_change_signature, 1);
>    bp_pack_value (&bp, node->local.redefined_extern_inline, 1);
> +  bp_pack_value (&bp, node->local.main_function, 1);
>    bp_pack_value (&bp, node->needed, 1);
>    bp_pack_value (&bp, node->address_taken, 1);
>    bp_pack_value (&bp, node->abstract_and_needed, 1);
> @@ -904,6 +905,7 @@ input_overwrite_node (struct lto_file_decl_data *file_data,
>    node->local.versionable = bp_unpack_value (bp, 1);
>    node->local.can_change_signature = bp_unpack_value (bp, 1);
>    node->local.redefined_extern_inline = bp_unpack_value (bp, 1);
> +  node->local.main_function = bp_unpack_value (bp, 1);
>    node->needed = bp_unpack_value (bp, 1);
>    node->address_taken = bp_unpack_value (bp, 1);
>    node->abstract_and_needed = bp_unpack_value (bp, 1);
> diff --git a/gcc/lto/lto-lang.c b/gcc/lto/lto-lang.c
> index 999db8b..a44a35f 100644
> --- a/gcc/lto/lto-lang.c
> +++ b/gcc/lto/lto-lang.c
> @@ -1137,13 +1137,6 @@ lto_init (void)
>    /* Create the basic integer types.  */
>    build_common_tree_nodes (flag_signed_char, /*short_double=*/false);
>  
> -  /* The global tree for the main identifier is filled in by
> -     language-specific front-end initialization that is not run in the
> -     LTO back-end.  It appears that all languages that perform such
> -     initialization currently do so in the same way, so we do it here.  */
> -  if (main_identifier_node == NULL_TREE)
> -    main_identifier_node = get_identifier ("main");
> -
>    /* In the C++ front-end, fileptr_type_node is defined as a variant
>       copy of of ptr_type_node, rather than ptr_node itself.  The
>       distinction should only be relevant to the front-end, so we
> diff --git a/gcc/predict.c b/gcc/predict.c
> index c12b45f..819e64c 100644
> --- a/gcc/predict.c
> +++ b/gcc/predict.c
> @@ -2275,7 +2275,7 @@ compute_function_frequency (void)
>    basic_block bb;
>    struct cgraph_node *node = cgraph_get_node (current_function_decl);
>    if (DECL_STATIC_CONSTRUCTOR (current_function_decl)
> -      || MAIN_NAME_P (DECL_NAME (current_function_decl)))
> +      || cgraph_main_function_p (node))
>      node->only_called_at_startup = true;
>    if (DECL_STATIC_DESTRUCTOR (current_function_decl))
>      node->only_called_at_exit = true;
> @@ -2291,7 +2291,7 @@ compute_function_frequency (void)
>          node->frequency = NODE_FREQUENCY_HOT;
>        else if (flags & ECF_NORETURN)
>          node->frequency = NODE_FREQUENCY_EXECUTED_ONCE;
> -      else if (MAIN_NAME_P (DECL_NAME (current_function_decl)))
> +      else if (cgraph_main_function_p (node))
>          node->frequency = NODE_FREQUENCY_EXECUTED_ONCE;
>        else if (DECL_STATIC_CONSTRUCTOR (current_function_decl)
>  	       || DECL_STATIC_DESTRUCTOR (current_function_decl))
> diff --git a/gcc/target.def b/gcc/target.def
> index d658b11..2c91620 100644
> --- a/gcc/target.def
> +++ b/gcc/target.def
> @@ -1473,6 +1473,17 @@ DEFHOOK
>   tree, (tree decl, tree  id),
>   default_mangle_decl_assembler_name)
>  
> +/* Return the assembler name for the 'main' function.  It should return the
> +   same identifier as mandle_decl_assembler_name will for the C 'main'
> +   function.
> +   The default is to return 'main'.  */
> +DEFHOOK
> +(main_assembler_name,
> + "It returns the assembler name for the 'main' function.\n\
> +The default is to return 'main', which will be prefixed by USER_LABEL_PREFIX.",
> + tree, (void),
> + default_main_assembler_name)
> +
>  /* Do something target-specific to record properties of the DECL into
>     the associated SYMBOL_REF.  */
>  DEFHOOK
> diff --git a/gcc/targhooks.c b/gcc/targhooks.c
> index 8e3d74e..08535b4 100644
> --- a/gcc/targhooks.c
> +++ b/gcc/targhooks.c
> @@ -371,6 +371,13 @@ default_mangle_assembler_name (const char *name ATTRIBUTE_UNUSED)
>    return get_identifier (stripped);
>  }
>  
> +/* The default implementation of TARGET_MAIN_ASSEMBLER_NAME.  */
> +tree
> +default_main_assembler_name (void)
> +{
> +  return get_identifier ("main");
> +}
> +
>  /* True if MODE is valid for the target.  By "valid", we mean able to
>     be manipulated in non-trivial ways.  In particular, this means all
>     the arithmetic is supported.
> diff --git a/gcc/targhooks.h b/gcc/targhooks.h
> index 8618115..3016f04 100644
> --- a/gcc/targhooks.h
> +++ b/gcc/targhooks.h
> @@ -66,6 +66,7 @@ extern void default_print_operand (FILE *, rtx, int);
>  extern void default_print_operand_address (FILE *, rtx);
>  extern bool default_print_operand_punct_valid_p (unsigned char);
>  extern tree default_mangle_assembler_name (const char *);
> +extern tree default_main_assembler_name (void);
>  
>  extern bool default_scalar_mode_supported_p (enum machine_mode);
>  extern bool targhook_words_big_endian (void);
> diff --git a/gcc/tree-ssa-structalias.c b/gcc/tree-ssa-structalias.c
> index b65f5aa..9cb7a16 100644
> --- a/gcc/tree-ssa-structalias.c
> +++ b/gcc/tree-ssa-structalias.c
> @@ -6933,7 +6933,7 @@ ipa_pta_execute (void)
>  
>  	  /* We also need to make function return values escape.  Nothing
>  	     escapes by returning from main though.  */
> -	  if (!MAIN_NAME_P (DECL_NAME (node->decl)))
> +	  if (!cgraph_main_function_p (node->decl))
>  	    {
>  	      varinfo_t fi, rvi;
>  	      fi = lookup_vi_for_tree (node->decl);
> diff --git a/gcc/tree.c b/gcc/tree.c
> index cfea9f7..6a0d380 100644
> --- a/gcc/tree.c
> +++ b/gcc/tree.c
> @@ -9477,6 +9477,8 @@ build_common_tree_nodes (bool signed_char, bool short_double)
>  
>      va_list_type_node = t;
>    }
> +
> +  main_assembler_name = targetm.main_assembler_name ();
>  }
>  
>  /* A subroutine of build_common_builtin_nodes.  Define a builtin function.  */
> diff --git a/gcc/tree.h b/gcc/tree.h
> index 62ee454..45c750f 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -3805,7 +3805,7 @@ enum tree_index
>  
>    TI_VOID_LIST_NODE,
>  
> -  TI_MAIN_IDENTIFIER,
> +  TI_MAIN_ASSEMBLER_NAME,
>  
>    TI_SAT_SFRACT_TYPE,
>    TI_SAT_FRACT_TYPE,
> @@ -4048,9 +4048,7 @@ extern GTY(()) tree global_trees[TI_MAX];
>     anything else about this node.  */
>  #define void_list_node                  global_trees[TI_VOID_LIST_NODE]
>  
> -#define main_identifier_node		global_trees[TI_MAIN_IDENTIFIER]
> -#define MAIN_NAME_P(NODE) \
> -  (IDENTIFIER_NODE_CHECK (NODE) == main_identifier_node)
> +#define main_assembler_name		global_trees[TI_MAIN_ASSEMBLER_NAME]
>  
>  /* Optimization options (OPTIMIZATION_NODE) to use for default and current
>     functions.  */
> 
> 

-- 
Richard Guenther <rguenther@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Tristan Gingold]

On Mar 20, 2012, at 5:01 PM, Richard Guenther wrote:

> On Tue, 20 Mar 2012, Tristan Gingold wrote:
> 
>> 
>> On Mar 20, 2012, at 3:19 PM, Richard Guenther wrote:
>> 
>> […]
>>> 
>>> I'd rather get away from using a global main_identifier_node, instead
>>> make that frontend specific, and introduce targetm.main_assembler_name
>>> which the assembler-name creating langhook would make sure to use
>>> when mangling what the FE thinks main is.  main_identifier_node should
>>> not serve any purpose outside of Frontends.
>>> 
>>> But I see both as a possible cleanup opportunity, not a necessary change.
>> 
>> Something along these lines ?
> 
> Yes, but I'd simply call the hook at the places you now use
> main_assembler_name and not create a global tree node for it.

But we use it at the beginning of graph_finalize_function, so caching it
makes sense, doesn't it ?

Tristan.

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Richard Guenther]

On Tue, 20 Mar 2012, Tristan Gingold wrote:

> 
> On Mar 20, 2012, at 5:01 PM, Richard Guenther wrote:
> 
> > On Tue, 20 Mar 2012, Tristan Gingold wrote:
> > 
> >> 
> >> On Mar 20, 2012, at 3:19 PM, Richard Guenther wrote:
> >> 
> >> [...]
> >>> 
> >>> I'd rather get away from using a global main_identifier_node, instead
> >>> make that frontend specific, and introduce targetm.main_assembler_name
> >>> which the assembler-name creating langhook would make sure to use
> >>> when mangling what the FE thinks main is.  main_identifier_node should
> >>> not serve any purpose outside of Frontends.
> >>> 
> >>> But I see both as a possible cleanup opportunity, not a necessary change.
> >> 
> >> Something along these lines ?
> > 
> > Yes, but I'd simply call the hook at the places you now use
> > main_assembler_name and not create a global tree node for it.
> 
> But we use it at the beginning of graph_finalize_function, so caching it
> makes sense, doesn't it ?

Well, maybe ;)  I have no strong opinion here.

Richard.

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Jan Hubicka]

> On Tue, 20 Mar 2012, Tristan Gingold wrote:
> 
> > 
> > On Mar 15, 2012, at 10:37 AM, Richard Guenther wrote:
> > 
> > > On Wed, 14 Mar 2012, Tristan Gingold wrote:
> > [?]
> > 
> > > 
> > > Well.  To make this work in LTO the "main" function (thus, the program
> > > entry point) should be marked at cgraph level and all users of
> > > MAIN_NAME_P should instead check a flag on the cgraph node.
> > > 
> > >> Will write a predicate in tree.[ch].
> > > 
> > > Please instead transition "main-ness" to the graph.

Yep, I also agree that it is something cgraph code should care about instead of
random placess across the whole middle-end.
> > diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
> > index bd21169..7a7a774 100644
> > --- a/gcc/cfgexpand.c
> > +++ b/gcc/cfgexpand.c
> > @@ -4513,9 +4513,8 @@ gimple_expand_cfg (void)
> >  
> >    /* If this function is `main', emit a call to `__main'
> >       to run global initializers, etc.  */
> > -  if (DECL_NAME (current_function_decl)
> > -      && MAIN_NAME_P (DECL_NAME (current_function_decl))
> > -      && DECL_FILE_SCOPE_P (current_function_decl))
> > +  if (DECL_FILE_SCOPE_P (current_function_decl)
> > +      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
> >      expand_main_function ();
> 
> The DECL_FILE_SCOPE_P check is redundant, please remove them everywhere
> you call cgraph_main_function_p.  I suppose returning false if the
> cgraph node is NULL in cgraph_main_function_p would be good.

How do we handle the cases before cgraph is built with this approach?
> > +/* Return true iff NODE is the main function (main in C).  */
> > +static inline bool
> > +cgraph_main_function_p (struct cgraph_node *node)
> > +{
> > +  return node->local.main_function;
> 
> node && node->local.main_function

Well, cgraph strategy is ito ICE when NODE is NULL :)
We could have cgraph_main_function_decl_p wrapper that does the NULL handling, but I still don't
see how this helps - i.e. when you don't have cgraph node you don't have info whether function
is main or not, so you should not even try to ask.
In what cases we ICE here?
> 
> > +}
> > +
> >  /* Walk all functions with body defined.  */
> >  #define FOR_EACH_FUNCTION_WITH_GIMPLE_BODY(node) \
> >     for ((node) = cgraph_first_function_with_gimple_body (); (node); \
> > diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
> > index 516f187..4a59f63 100644
> > --- a/gcc/cgraphunit.c
> > +++ b/gcc/cgraphunit.c
> > @@ -346,6 +346,10 @@ cgraph_finalize_function (tree decl, bool nested)
> >    notice_global_symbol (decl);
> >    node->local.finalized = true;
> >    node->lowered = DECL_STRUCT_FUNCTION (decl)->cfg != NULL;
> > +  node->local.main_function =
> > +    DECL_FILE_SCOPE_P (decl)
> > +    && ((!DECL_ASSEMBLER_NAME_SET_P (decl) && MAIN_NAME_P (DECL_NAME (decl)))
> > +	|| decl_assembler_name_equal (decl, main_identifier_node));
> 
> If we finalize a function we should always create an assembler name,
> thus I'd change the above to
> 
>   node->local.main_function = decl_assembler_name_equal (decl, 
> main_identifier_node);
> 
> btw, decl_assembler_name_equal doesn't seem to remove target-specific
> mangling - do some OSes "mangle" main differently (I'm thinking of
> leading underscores or complete renames)?  Thus, I guess the
> targets might want to be able to provide the main_identifier_assember_name
> you use here.

Yes, name function is mangled, i.e. it is _main on djgpp as long as I remember.
This is why we have the main_identifier_node to go through the mandling procedure.

Honza

Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Tristan Gingold]

On Mar 20, 2012, at 6:17 PM, Jan Hubicka wrote:

>> On Tue, 20 Mar 2012, Tristan Gingold wrote:
>> 
>>> 
>>> On Mar 15, 2012, at 10:37 AM, Richard Guenther wrote:
>>> 
>>>> On Wed, 14 Mar 2012, Tristan Gingold wrote:
>>> [?]
>>> 
>>>> 
>>>> Well.  To make this work in LTO the "main" function (thus, the program
>>>> entry point) should be marked at cgraph level and all users of
>>>> MAIN_NAME_P should instead check a flag on the cgraph node.
>>>> 
>>>>> Will write a predicate in tree.[ch].
>>>> 
>>>> Please instead transition "main-ness" to the graph.
> 
> Yep, I also agree that it is something cgraph code should care about instead of
> random placess across the whole middle-end.
>>> diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
>>> index bd21169..7a7a774 100644
>>> --- a/gcc/cfgexpand.c
>>> +++ b/gcc/cfgexpand.c
>>> @@ -4513,9 +4513,8 @@ gimple_expand_cfg (void)
>>> 
>>>   /* If this function is `main', emit a call to `__main'
>>>      to run global initializers, etc.  */
>>> -  if (DECL_NAME (current_function_decl)
>>> -      && MAIN_NAME_P (DECL_NAME (current_function_decl))
>>> -      && DECL_FILE_SCOPE_P (current_function_decl))
>>> +  if (DECL_FILE_SCOPE_P (current_function_decl)
>>> +      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
>>>     expand_main_function ();
>> 
>> The DECL_FILE_SCOPE_P check is redundant, please remove them everywhere
>> you call cgraph_main_function_p.  I suppose returning false if the
>> cgraph node is NULL in cgraph_main_function_p would be good.
> 
> How do we handle the cases before cgraph is built with this approach?

Only front-end code need to check wether a function is main before they add
it in cgraph.  As each front-end should know which function is main, this is
not an issue for them.

>>> +/* Return true iff NODE is the main function (main in C).  */
>>> +static inline bool
>>> +cgraph_main_function_p (struct cgraph_node *node)
>>> +{
>>> +  return node->local.main_function;
>> 
>> node && node->local.main_function
> 
> Well, cgraph strategy is ito ICE when NODE is NULL :)
> We could have cgraph_main_function_decl_p wrapper that does the NULL handling, but I still don't
> see how this helps - i.e. when you don't have cgraph node you don't have info whether function
> is main or not, so you should not even try to ask.
> In what cases we ICE here?

We don't ICE here - as long as graph_main_function_p is called after front-end.

>>> +}
>>> +
>>> /* Walk all functions with body defined.  */
>>> #define FOR_EACH_FUNCTION_WITH_GIMPLE_BODY(node) \
>>>    for ((node) = cgraph_first_function_with_gimple_body (); (node); \
>>> diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
>>> index 516f187..4a59f63 100644
>>> --- a/gcc/cgraphunit.c
>>> +++ b/gcc/cgraphunit.c
>>> @@ -346,6 +346,10 @@ cgraph_finalize_function (tree decl, bool nested)
>>>   notice_global_symbol (decl);
>>>   node->local.finalized = true;
>>>   node->lowered = DECL_STRUCT_FUNCTION (decl)->cfg != NULL;
>>> +  node->local.main_function =
>>> +    DECL_FILE_SCOPE_P (decl)
>>> +    && ((!DECL_ASSEMBLER_NAME_SET_P (decl) && MAIN_NAME_P (DECL_NAME (decl)))
>>> +	||decl_assembler_name_equal (decl, main_identifier_node));
>> 
>> If we finalize a function we should always create an assembler name,
>> thus I'd change the above to
>> 
>>  node->local.main_function = decl_assembler_name_equal (decl, 
>> main_identifier_node);
>> 
>> btw, decl_assembler_name_equal doesn't seem to remove target-specific
>> mangling - do some OSes "mangle" main differently (I'm thinking of
>> leading underscores or complete renames)?  Thus, I guess the
>> targets might want to be able to provide the main_identifier_assember_name
>> you use here.
> 
> Yes, name function is mangled, i.e. it is _main on djgpp as long as I remember.
> This is why we have the main_identifier_node to go through the mandling procedure.


USER_LABEL_PREFIX is handled by decl_assembler_name_equal.

One way to simplify that is to change the NESTED argument of cgraph_finalize_function
to LEVEL, which could be either main, top or nested.  With this mechanism, every
front-end will explicitly tell to the middle-end which function is the main entry point.

Thoughts ?

Tristan.

whic