Struct declaration and initialization in TREES

Struct declaration and initialization in TREES

[Erick Ochoa]

Hi,

I'm interested in printing VAR_DECL trees that are of type
RECORD_TYPE. I am using the function print_generic_decl
for debugging and found this interesting behaviour.

When I do initialization of structs using the following
syntax:

```
struct aStruct { _Bool e; int a; char b; float c; double d; _Bool f; long h;};
struct aStruct astruct = { .e = 0, .a = 1, .b = 2, .c = 3.0, .d = 4.0, .f = 5, .h = 6 };
```

print_generic_decl will print the following output:

```
INTERESTED IN:   static struct aStruct astruct = <<< error >>>;
```

Am I using the correct API? Is this a limitation of the API?
Would people be interested in me extending this API to print
out something more useful? I already have some code that
iterates over fields and prints out names and types. It
can still use some work though.

However, I understand if this is the intended behaviour.
Another question (related to the possibility of intended behaviour)
is: how is struct initialization represented in trees?
(I.e. will each field be initialized separately or something else
happens?)

Thanks! I also include the patch in case people want a simple
working example on how to print declarations.

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 6b857bd..f4f1376 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -1368,6 +1368,7 @@ OBJS = \
 	incpath.o \
 	init-regs.o \
 	internal-fn.o \
+	ipa-hello-world.o \
 	ipa-cp.o \
 	ipa-sra.o \
 	ipa-devirt.o \
diff --git a/gcc/common.opt b/gcc/common.opt
index b4dc31c..304ec9f 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -3348,4 +3348,7 @@ fipa-ra
 Common Report Var(flag_ipa_ra) Optimization
 Use caller save register across calls if possible.
 
+fipa-typelist
+Common Report Var(flag_ipa_typelist) TBD
+
 ; This comment is to ensure we retain the blank line above.
diff --git a/gcc/ipa-hello-world.c b/gcc/ipa-hello-world.c
new file mode 100644
index 0000000..ed4ae11
--- /dev/null
+++ b/gcc/ipa-hello-world.c
@@ -0,0 +1,78 @@
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "backend.h"
+#include "tree.h"
+#include "gimple-expr.h"
+#include "predict.h"
+#include "alloc-pool.h"
+#include "tree-pass.h"
+#include "cgraph.h"
+#include "diagnostic.h"
+#include "fold-const.h"
+#include "gimple-fold.h"
+#include "symbol-summary.h"
+#include "tree-vrp.h"
+#include "ipa-prop.h"
+#include "tree-pretty-print.h"
+#include "tree-inline.h"
+#include "ipa-fnsummary.h"
+#include "ipa-utils.h"
+#include "tree-ssa-ccp.h"
+#include "stringpool.h"
+#include "attribs.h"
+
+
+static unsigned int
+iphw_execute()
+{
+  if (!dump_file) return 0;
+  varpool_node *node;
+  FOR_EACH_VARIABLE(node)
+  {
+    gcc_assert(node->decl);
+    tree decl = node->decl;
+    gcc_assert(TREE_CODE(decl) == VAR_DECL);
+
+    tree curr_type = TREE_TYPE(decl);
+    gcc_assert(curr_type);
+
+    const bool is_struct = TREE_CODE(curr_type) == RECORD_TYPE;
+    if (is_struct) fprintf(dump_file, "INTERESTED IN: ");
+    print_generic_decl(dump_file, decl, TDF_DETAILS);
+    fprintf(dump_file, "\n");
+  }
+  return 0;
+}
+
+namespace {
+const pass_data pass_data_ipa_hello_world =
+{
+  SIMPLE_IPA_PASS,
+  "hello_world",
+  OPTGROUP_NONE,
+  TV_NONE,
+  (PROP_cfg | PROP_ssa),
+  0,
+  0,
+  0,
+  0,
+};
+
+class pass_ipa_hello_world : public simple_ipa_opt_pass
+{
+public:
+  pass_ipa_hello_world (gcc::context *ctx)
+    : simple_ipa_opt_pass(pass_data_ipa_hello_world, ctx)
+  {}
+
+  virtual bool gate(function*) { return flag_ipa_typelist; }
+  virtual unsigned execute (function*) { return iphw_execute(); }
+};
+} // anon namespace
+
+simple_ipa_opt_pass*
+make_pass_ipa_hello_world (gcc::context *ctx)
+{
+  return new pass_ipa_hello_world (ctx);
+}
diff --git a/gcc/passes.def b/gcc/passes.def
index 798a391..52cd14b 100644
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -146,6 +146,7 @@ along with GCC; see the file COPYING3.  If not see
   NEXT_PASS (pass_ipa_profile);
   NEXT_PASS (pass_ipa_icf);
   NEXT_PASS (pass_ipa_devirt);
+  NEXT_PASS (pass_ipa_hello_world);
   NEXT_PASS (pass_ipa_cp);
   NEXT_PASS (pass_ipa_sra);
   NEXT_PASS (pass_ipa_cdtor_merge);
diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
index a987661..915fc69 100644
--- a/gcc/tree-pass.h
+++ b/gcc/tree-pass.h
@@ -498,6 +498,7 @@ extern ipa_opt_pass_d *make_pass_ipa_fn_summary (gcc::context *ctxt);
 extern ipa_opt_pass_d *make_pass_ipa_inline (gcc::context *ctxt);
 extern simple_ipa_opt_pass *make_pass_ipa_free_lang_data (gcc::context *ctxt);
 extern simple_ipa_opt_pass *make_pass_ipa_free_fn_summary (gcc::context *ctxt);
+extern simple_ipa_opt_pass *make_pass_ipa_hello_world (gcc::context *ctxt);
 extern ipa_opt_pass_d *make_pass_ipa_cp (gcc::context *ctxt);
 extern ipa_opt_pass_d *make_pass_ipa_sra (gcc::context *ctxt);
 extern ipa_opt_pass_d *make_pass_ipa_icf (gcc::context *ctxt);

Re: Struct declaration and initialization in TREES

[Richard Biener]

On December 17, 2019 8:31:00 PM GMT+01:00, Erick Ochoa <erick.ochoa@theobroma-systems.com> wrote:
>Hi,
>
>I'm interested in printing VAR_DECL trees that are of type
>RECORD_TYPE. I am using the function print_generic_decl
>for debugging and found this interesting behaviour.
>
>When I do initialization of structs using the following
>syntax:
>
>```
>struct aStruct { _Bool e; int a; char b; float c; double d; _Bool f;
>long h;};
>struct aStruct astruct = { .e = 0, .a = 1, .b = 2, .c = 3.0, .d = 4.0,
>.f = 5, .h = 6 };
>```
>
>print_generic_decl will print the following output:
>
>```
>INTERESTED IN:   static struct aStruct astruct = <<< error >>>;
>```
>
>Am I using the correct API? Is this a limitation of the API?

You need to ask IPA about the static initializer, DECL_INITIAL is adjusted at some point. 

Richard. 

>Would people be interested in me extending this API to print
>out something more useful? I already have some code that
>iterates over fields and prints out names and types. It
>can still use some work though.
>
>However, I understand if this is the intended behaviour.
>Another question (related to the possibility of intended behaviour)
>is: how is struct initialization represented in trees?
>(I.e. will each field be initialized separately or something else
>happens?)
>
>Thanks! I also include the patch in case people want a simple
>working example on how to print declarations.
>
>diff --git a/gcc/Makefile.in b/gcc/Makefile.in
>index 6b857bd..f4f1376 100644
>--- a/gcc/Makefile.in
>+++ b/gcc/Makefile.in
>@@ -1368,6 +1368,7 @@ OBJS = \
> 	incpath.o \
> 	init-regs.o \
> 	internal-fn.o \
>+	ipa-hello-world.o \
> 	ipa-cp.o \
> 	ipa-sra.o \
> 	ipa-devirt.o \
>diff --git a/gcc/common.opt b/gcc/common.opt
>index b4dc31c..304ec9f 100644
>--- a/gcc/common.opt
>+++ b/gcc/common.opt
>@@ -3348,4 +3348,7 @@ fipa-ra
> Common Report Var(flag_ipa_ra) Optimization
> Use caller save register across calls if possible.
> 
>+fipa-typelist
>+Common Report Var(flag_ipa_typelist) TBD
>+
> ; This comment is to ensure we retain the blank line above.
>diff --git a/gcc/ipa-hello-world.c b/gcc/ipa-hello-world.c
>new file mode 100644
>index 0000000..ed4ae11
>--- /dev/null
>+++ b/gcc/ipa-hello-world.c
>@@ -0,0 +1,78 @@
>+#include "config.h"
>+#include "system.h"
>+#include "coretypes.h"
>+#include "backend.h"
>+#include "tree.h"
>+#include "gimple-expr.h"
>+#include "predict.h"
>+#include "alloc-pool.h"
>+#include "tree-pass.h"
>+#include "cgraph.h"
>+#include "diagnostic.h"
>+#include "fold-const.h"
>+#include "gimple-fold.h"
>+#include "symbol-summary.h"
>+#include "tree-vrp.h"
>+#include "ipa-prop.h"
>+#include "tree-pretty-print.h"
>+#include "tree-inline.h"
>+#include "ipa-fnsummary.h"
>+#include "ipa-utils.h"
>+#include "tree-ssa-ccp.h"
>+#include "stringpool.h"
>+#include "attribs.h"
>+
>+
>+static unsigned int
>+iphw_execute()
>+{
>+  if (!dump_file) return 0;
>+  varpool_node *node;
>+  FOR_EACH_VARIABLE(node)
>+  {
>+    gcc_assert(node->decl);
>+    tree decl = node->decl;
>+    gcc_assert(TREE_CODE(decl) == VAR_DECL);
>+
>+    tree curr_type = TREE_TYPE(decl);
>+    gcc_assert(curr_type);
>+
>+    const bool is_struct = TREE_CODE(curr_type) == RECORD_TYPE;
>+    if (is_struct) fprintf(dump_file, "INTERESTED IN: ");
>+    print_generic_decl(dump_file, decl, TDF_DETAILS);
>+    fprintf(dump_file, "\n");
>+  }
>+  return 0;
>+}
>+
>+namespace {
>+const pass_data pass_data_ipa_hello_world =
>+{
>+  SIMPLE_IPA_PASS,
>+  "hello_world",
>+  OPTGROUP_NONE,
>+  TV_NONE,
>+  (PROP_cfg | PROP_ssa),
>+  0,
>+  0,
>+  0,
>+  0,
>+};
>+
>+class pass_ipa_hello_world : public simple_ipa_opt_pass
>+{
>+public:
>+  pass_ipa_hello_world (gcc::context *ctx)
>+    : simple_ipa_opt_pass(pass_data_ipa_hello_world, ctx)
>+  {}
>+
>+  virtual bool gate(function*) { return flag_ipa_typelist; }
>+  virtual unsigned execute (function*) { return iphw_execute(); }
>+};
>+} // anon namespace
>+
>+simple_ipa_opt_pass*
>+make_pass_ipa_hello_world (gcc::context *ctx)
>+{
>+  return new pass_ipa_hello_world (ctx);
>+}
>diff --git a/gcc/passes.def b/gcc/passes.def
>index 798a391..52cd14b 100644
>--- a/gcc/passes.def
>+++ b/gcc/passes.def
>@@ -146,6 +146,7 @@ along with GCC; see the file COPYING3.  If not see
>   NEXT_PASS (pass_ipa_profile);
>   NEXT_PASS (pass_ipa_icf);
>   NEXT_PASS (pass_ipa_devirt);
>+  NEXT_PASS (pass_ipa_hello_world);
>   NEXT_PASS (pass_ipa_cp);
>   NEXT_PASS (pass_ipa_sra);
>   NEXT_PASS (pass_ipa_cdtor_merge);
>diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
>index a987661..915fc69 100644
>--- a/gcc/tree-pass.h
>+++ b/gcc/tree-pass.h
>@@ -498,6 +498,7 @@ extern ipa_opt_pass_d *make_pass_ipa_fn_summary
>(gcc::context *ctxt);
> extern ipa_opt_pass_d *make_pass_ipa_inline (gcc::context *ctxt);
>extern simple_ipa_opt_pass *make_pass_ipa_free_lang_data (gcc::context
>*ctxt);
>extern simple_ipa_opt_pass *make_pass_ipa_free_fn_summary (gcc::context
>*ctxt);
>+extern simple_ipa_opt_pass *make_pass_ipa_hello_world (gcc::context
>*ctxt);
> extern ipa_opt_pass_d *make_pass_ipa_cp (gcc::context *ctxt);
> extern ipa_opt_pass_d *make_pass_ipa_sra (gcc::context *ctxt);
> extern ipa_opt_pass_d *make_pass_ipa_icf (gcc::context *ctxt);

Re: Struct declaration and initialization in TREES

[Erick Ochoa]

On 2019-12-18 6:02 a.m., Richard Biener wrote:
> On December 17, 2019 8:31:00 PM GMT+01:00, Erick Ochoa <erick.ochoa@theobroma-systems.com> wrote:
>> Hi,
>>
>> I'm interested in printing VAR_DECL trees that are of type
>> RECORD_TYPE. I am using the function print_generic_decl
>> for debugging and found this interesting behaviour.
>>
>> When I do initialization of structs using the following
>> syntax:
>>
>> ```
>> struct aStruct { _Bool e; int a; char b; float c; double d; _Bool f;
>> long h;};
>> struct aStruct astruct = { .e = 0, .a = 1, .b = 2, .c = 3.0, .d = 4.0,
>> .f = 5, .h = 6 };
>> ```
>>
>> print_generic_decl will print the following output:
>>
>> ```
>> INTERESTED IN:   static struct aStruct astruct = <<< error >>>;
>> ```
>>
>> Am I using the correct API? Is this a limitation of the API?
> 
> You need to ask IPA about the static initializer, DECL_INITIAL is adjusted at some point. 
> 
> Richard. 

Thanks Richard.

I still don't understand very well what I should do. I found the
place in GCC internals where DECL_INITIAL is described.

https://gcc.gnu.org/onlinedocs/gccint/Working-with-declarations.html

VAR_DECL

  If this variable is initialized (but does not require a constructor),
  the DECL_INITIAL will be an expression for the initializer.
  The initializer should be evaluated, and a bitwise copy into the variable
  performed. If the DECL_INITIAL is the error_mark_node, there is an initializer,
  but it is given by an explicit statement later in the code; no bitwise copy is required.

So, now I understand that I can now change my patch to something like this:

>> +iphw_execute()
>> +{
>> +  if (!dump_file) return 0;
>> +  varpool_node *node;
>> +  FOR_EACH_VARIABLE(node)
>> +  {
>> +    gcc_assert(node->decl);
>> +    tree decl = node->decl;
>> +    gcc_assert(TREE_CODE(decl) == VAR_DECL);
>> +
>> +    tree curr_type = TREE_TYPE(decl);
>> +    gcc_assert(curr_type);
>> +
>> +    const bool is_struct = TREE_CODE(curr_type) == RECORD_TYPE;
>> +    if (is_struct) fprintf(dump_file, "INTERESTED IN: ");
 
        tree expr = DECL_INITIAL(decl);
        if (expr == error_mark_node) {
           fprintf(dump_file, "initializer is given by explicit statement later in code\n");
           continue;
        }

>> +    print_generic_decl(dump_file, decl, TDF_DETAILS);
>> +    fprintf(dump_file, "\n");
>> +  }

However I still don't know how to ask IPA about the static initializer.
I tried iterating over the ipa_refs (i.e.  node->iterate_referring (i, ref))
and then looking for writes, but there are now writes because it is a
initialized statically.

> 
>> Would people be interested in me extending this API to print
>> out something more useful? I already have some code that
>> iterates over fields and prints out names and types. It
>> can still use some work though.
>>
>> However, I understand if this is the intended behaviour.
>> Another question (related to the possibility of intended behaviour)
>> is: how is struct initialization represented in trees?
>> (I.e. will each field be initialized separately or something else
>> happens?)
>>
>> Thanks! I also include the patch in case people want a simple
>> working example on how to print declarations.
>>
>> diff --git a/gcc/Makefile.in b/gcc/Makefile.in
>> index 6b857bd..f4f1376 100644
>> --- a/gcc/Makefile.in
>> +++ b/gcc/Makefile.in
>> @@ -1368,6 +1368,7 @@ OBJS = \
>> 	incpath.o \
>> 	init-regs.o \
>> 	internal-fn.o \
>> +	ipa-hello-world.o \
>> 	ipa-cp.o \
>> 	ipa-sra.o \
>> 	ipa-devirt.o \
>> diff --git a/gcc/common.opt b/gcc/common.opt
>> index b4dc31c..304ec9f 100644
>> --- a/gcc/common.opt
>> +++ b/gcc/common.opt
>> @@ -3348,4 +3348,7 @@ fipa-ra
>> Common Report Var(flag_ipa_ra) Optimization
>> Use caller save register across calls if possible.
>>
>> +fipa-typelist
>> +Common Report Var(flag_ipa_typelist) TBD
>> +
>> ; This comment is to ensure we retain the blank line above.
>> diff --git a/gcc/ipa-hello-world.c b/gcc/ipa-hello-world.c
>> new file mode 100644
>> index 0000000..ed4ae11
>> --- /dev/null
>> +++ b/gcc/ipa-hello-world.c
>> @@ -0,0 +1,78 @@
>> +#include "config.h"
>> +#include "system.h"
>> +#include "coretypes.h"
>> +#include "backend.h"
>> +#include "tree.h"
>> +#include "gimple-expr.h"
>> +#include "predict.h"
>> +#include "alloc-pool.h"
>> +#include "tree-pass.h"
>> +#include "cgraph.h"
>> +#include "diagnostic.h"
>> +#include "fold-const.h"
>> +#include "gimple-fold.h"
>> +#include "symbol-summary.h"
>> +#include "tree-vrp.h"
>> +#include "ipa-prop.h"
>> +#include "tree-pretty-print.h"
>> +#include "tree-inline.h"
>> +#include "ipa-fnsummary.h"
>> +#include "ipa-utils.h"
>> +#include "tree-ssa-ccp.h"
>> +#include "stringpool.h"
>> +#include "attribs.h"
>> +
>> +
>> +static unsigned int
>> +iphw_execute()
>> +{
>> +  if (!dump_file) return 0;
>> +  varpool_node *node;
>> +  FOR_EACH_VARIABLE(node)
>> +  {
>> +    gcc_assert(node->decl);
>> +    tree decl = node->decl;
>> +    gcc_assert(TREE_CODE(decl) == VAR_DECL);
>> +
>> +    tree curr_type = TREE_TYPE(decl);
>> +    gcc_assert(curr_type);
>> +
>> +    const bool is_struct = TREE_CODE(curr_type) == RECORD_TYPE;
>> +    if (is_struct) fprintf(dump_file, "INTERESTED IN: ");
>> +    print_generic_decl(dump_file, decl, TDF_DETAILS);
>> +    fprintf(dump_file, "\n");
>> +  }
>> +  return 0;
>> +}
>> +
>> +namespace {
>> +const pass_data pass_data_ipa_hello_world =
>> +{
>> +  SIMPLE_IPA_PASS,
>> +  "hello_world",
>> +  OPTGROUP_NONE,
>> +  TV_NONE,
>> +  (PROP_cfg | PROP_ssa),
>> +  0,
>> +  0,
>> +  0,
>> +  0,
>> +};
>> +
>> +class pass_ipa_hello_world : public simple_ipa_opt_pass
>> +{
>> +public:
>> +  pass_ipa_hello_world (gcc::context *ctx)
>> +    : simple_ipa_opt_pass(pass_data_ipa_hello_world, ctx)
>> +  {}
>> +
>> +  virtual bool gate(function*) { return flag_ipa_typelist; }
>> +  virtual unsigned execute (function*) { return iphw_execute(); }
>> +};
>> +} // anon namespace
>> +
>> +simple_ipa_opt_pass*
>> +make_pass_ipa_hello_world (gcc::context *ctx)
>> +{
>> +  return new pass_ipa_hello_world (ctx);
>> +}
>> diff --git a/gcc/passes.def b/gcc/passes.def
>> index 798a391..52cd14b 100644
>> --- a/gcc/passes.def
>> +++ b/gcc/passes.def
>> @@ -146,6 +146,7 @@ along with GCC; see the file COPYING3.  If not see
>>   NEXT_PASS (pass_ipa_profile);
>>   NEXT_PASS (pass_ipa_icf);
>>   NEXT_PASS (pass_ipa_devirt);
>> +  NEXT_PASS (pass_ipa_hello_world);
>>   NEXT_PASS (pass_ipa_cp);
>>   NEXT_PASS (pass_ipa_sra);
>>   NEXT_PASS (pass_ipa_cdtor_merge);
>> diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
>> index a987661..915fc69 100644
>> --- a/gcc/tree-pass.h
>> +++ b/gcc/tree-pass.h
>> @@ -498,6 +498,7 @@ extern ipa_opt_pass_d *make_pass_ipa_fn_summary
>> (gcc::context *ctxt);
>> extern ipa_opt_pass_d *make_pass_ipa_inline (gcc::context *ctxt);
>> extern simple_ipa_opt_pass *make_pass_ipa_free_lang_data (gcc::context
>> *ctxt);
>> extern simple_ipa_opt_pass *make_pass_ipa_free_fn_summary (gcc::context
>> *ctxt);
>> +extern simple_ipa_opt_pass *make_pass_ipa_hello_world (gcc::context
>> *ctxt);
>> extern ipa_opt_pass_d *make_pass_ipa_cp (gcc::context *ctxt);
>> extern ipa_opt_pass_d *make_pass_ipa_sra (gcc::context *ctxt);
>> extern ipa_opt_pass_d *make_pass_ipa_icf (gcc::context *ctxt);
> 

Re: Struct declaration and initialization in TREES

[Erick Ochoa]

On 2019-12-18 1:33 p.m., Erick Ochoa wrote:
> 
> 
> On 2019-12-18 6:02 a.m., Richard Biener wrote:
>> On December 17, 2019 8:31:00 PM GMT+01:00, Erick Ochoa <erick.ochoa@theobroma-systems.com> wrote:
>>> Hi,
>>>
>>> I'm interested in printing VAR_DECL trees that are of type
>>> RECORD_TYPE. I am using the function print_generic_decl
>>> for debugging and found this interesting behaviour.
>>>
>>> When I do initialization of structs using the following
>>> syntax:
>>>
>>> ```
>>> struct aStruct { _Bool e; int a; char b; float c; double d; _Bool f;
>>> long h;};
>>> struct aStruct astruct = { .e = 0, .a = 1, .b = 2, .c = 3.0, .d = 4.0,
>>> .f = 5, .h = 6 };
>>> ```
>>>
>>> print_generic_decl will print the following output:
>>>
>>> ```
>>> INTERESTED IN:   static struct aStruct astruct = <<< error >>>;
>>> ```
>>>
>>> Am I using the correct API? Is this a limitation of the API?
>>
>> You need to ask IPA about the static initializer, DECL_INITIAL is adjusted at some point. 
>>
>> Richard. 
> 
> Thanks Richard.
> 
> I still don't understand very well what I should do. I found the
> place in GCC internals where DECL_INITIAL is described.
> 
> https://gcc.gnu.org/onlinedocs/gccint/Working-with-declarations.html
> 
> VAR_DECL
> 
>   If this variable is initialized (but does not require a constructor),
>   the DECL_INITIAL will be an expression for the initializer.
>   The initializer should be evaluated, and a bitwise copy into the variable
>   performed. If the DECL_INITIAL is the error_mark_node, there is an initializer,
>   but it is given by an explicit statement later in the code; no bitwise copy is required.
> 
> So, now I understand that I can now change my patch to something like this:
> 
>>> +iphw_execute()
>>> +{
>>> +  if (!dump_file) return 0;
>>> +  varpool_node *node;
>>> +  FOR_EACH_VARIABLE(node)
>>> +  {
>>> +    gcc_assert(node->decl);
>>> +    tree decl = node->decl;
>>> +    gcc_assert(TREE_CODE(decl) == VAR_DECL);
>>> +
>>> +    tree curr_type = TREE_TYPE(decl);
>>> +    gcc_assert(curr_type);
>>> +
>>> +    const bool is_struct = TREE_CODE(curr_type) == RECORD_TYPE;
>>> +    if (is_struct) fprintf(dump_file, "INTERESTED IN: ");
>  
>         tree expr = DECL_INITIAL(decl);
>         if (expr == error_mark_node) {
>            fprintf(dump_file, "initializer is given by explicit statement later in code\n");
>            continue;
>         }
> 
>>> +    print_generic_decl(dump_file, decl, TDF_DETAILS);
>>> +    fprintf(dump_file, "\n");
>>> +  }
> 
> However I still don't know how to ask IPA about the static initializer.
> I tried iterating over the ipa_refs (i.e.  node->iterate_referring (i, ref))
> and then looking for writes, but there are now writes because it is a
> initialized statically.

I found some more documentation about static initializers
during LTO. In GCC internals it says:
https://gcc.gnu.org/onlinedocs/gccint/LTO-object-file-layout.html#LTO-object-file-layout

  Static variable initializers (.gnu.lto_.vars)

  This section contains all the symbols in the global variable pool. It is
  emitted by lto-cgraph.c:output_varpool and read in lto-cgraph.c:input_cgraph.

Does this mean that I should load an LTO_section and read the information?

However, I'm still a bit confused since I believe input_cgraph gets called
before my pass. My pass is running during WPA. Besides, I can inspect the
initializers for other variables just not those of structs.

Any help will be appreciated. Thanks again!

> 
>>
>>> Would people be interested in me extending this API to print
>>> out something more useful? I already have some code that
>>> iterates over fields and prints out names and types. It
>>> can still use some work though.
>>>
>>> However, I understand if this is the intended behaviour.
>>> Another question (related to the possibility of intended behaviour)
>>> is: how is struct initialization represented in trees?
>>> (I.e. will each field be initialized separately or something else
>>> happens?)
>>>
>>> Thanks! I also include the patch in case people want a simple
>>> working example on how to print declarations.
>>>
>>> diff --git a/gcc/Makefile.in b/gcc/Makefile.in
>>> index 6b857bd..f4f1376 100644
>>> --- a/gcc/Makefile.in
>>> +++ b/gcc/Makefile.in
>>> @@ -1368,6 +1368,7 @@ OBJS = \
>>> 	incpath.o \
>>> 	init-regs.o \
>>> 	internal-fn.o \
>>> +	ipa-hello-world.o \
>>> 	ipa-cp.o \
>>> 	ipa-sra.o \
>>> 	ipa-devirt.o \
>>> diff --git a/gcc/common.opt b/gcc/common.opt
>>> index b4dc31c..304ec9f 100644
>>> --- a/gcc/common.opt
>>> +++ b/gcc/common.opt
>>> @@ -3348,4 +3348,7 @@ fipa-ra
>>> Common Report Var(flag_ipa_ra) Optimization
>>> Use caller save register across calls if possible.
>>>
>>> +fipa-typelist
>>> +Common Report Var(flag_ipa_typelist) TBD
>>> +
>>> ; This comment is to ensure we retain the blank line above.
>>> diff --git a/gcc/ipa-hello-world.c b/gcc/ipa-hello-world.c
>>> new file mode 100644
>>> index 0000000..ed4ae11
>>> --- /dev/null
>>> +++ b/gcc/ipa-hello-world.c
>>> @@ -0,0 +1,78 @@
>>> +#include "config.h"
>>> +#include "system.h"
>>> +#include "coretypes.h"
>>> +#include "backend.h"
>>> +#include "tree.h"
>>> +#include "gimple-expr.h"
>>> +#include "predict.h"
>>> +#include "alloc-pool.h"
>>> +#include "tree-pass.h"
>>> +#include "cgraph.h"
>>> +#include "diagnostic.h"
>>> +#include "fold-const.h"
>>> +#include "gimple-fold.h"
>>> +#include "symbol-summary.h"
>>> +#include "tree-vrp.h"
>>> +#include "ipa-prop.h"
>>> +#include "tree-pretty-print.h"
>>> +#include "tree-inline.h"
>>> +#include "ipa-fnsummary.h"
>>> +#include "ipa-utils.h"
>>> +#include "tree-ssa-ccp.h"
>>> +#include "stringpool.h"
>>> +#include "attribs.h"
>>> +
>>> +
>>> +static unsigned int
>>> +iphw_execute()
>>> +{
>>> +  if (!dump_file) return 0;
>>> +  varpool_node *node;
>>> +  FOR_EACH_VARIABLE(node)
>>> +  {
>>> +    gcc_assert(node->decl);
>>> +    tree decl = node->decl;
>>> +    gcc_assert(TREE_CODE(decl) == VAR_DECL);
>>> +
>>> +    tree curr_type = TREE_TYPE(decl);
>>> +    gcc_assert(curr_type);
>>> +
>>> +    const bool is_struct = TREE_CODE(curr_type) == RECORD_TYPE;
>>> +    if (is_struct) fprintf(dump_file, "INTERESTED IN: ");
>>> +    print_generic_decl(dump_file, decl, TDF_DETAILS);
>>> +    fprintf(dump_file, "\n");
>>> +  }
>>> +  return 0;
>>> +}
>>> +
>>> +namespace {
>>> +const pass_data pass_data_ipa_hello_world =
>>> +{
>>> +  SIMPLE_IPA_PASS,
>>> +  "hello_world",
>>> +  OPTGROUP_NONE,
>>> +  TV_NONE,
>>> +  (PROP_cfg | PROP_ssa),
>>> +  0,
>>> +  0,
>>> +  0,
>>> +  0,
>>> +};
>>> +
>>> +class pass_ipa_hello_world : public simple_ipa_opt_pass
>>> +{
>>> +public:
>>> +  pass_ipa_hello_world (gcc::context *ctx)
>>> +    : simple_ipa_opt_pass(pass_data_ipa_hello_world, ctx)
>>> +  {}
>>> +
>>> +  virtual bool gate(function*) { return flag_ipa_typelist; }
>>> +  virtual unsigned execute (function*) { return iphw_execute(); }
>>> +};
>>> +} // anon namespace
>>> +
>>> +simple_ipa_opt_pass*
>>> +make_pass_ipa_hello_world (gcc::context *ctx)
>>> +{
>>> +  return new pass_ipa_hello_world (ctx);
>>> +}
>>> diff --git a/gcc/passes.def b/gcc/passes.def
>>> index 798a391..52cd14b 100644
>>> --- a/gcc/passes.def
>>> +++ b/gcc/passes.def
>>> @@ -146,6 +146,7 @@ along with GCC; see the file COPYING3.  If not see
>>>   NEXT_PASS (pass_ipa_profile);
>>>   NEXT_PASS (pass_ipa_icf);
>>>   NEXT_PASS (pass_ipa_devirt);
>>> +  NEXT_PASS (pass_ipa_hello_world);
>>>   NEXT_PASS (pass_ipa_cp);
>>>   NEXT_PASS (pass_ipa_sra);
>>>   NEXT_PASS (pass_ipa_cdtor_merge);
>>> diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
>>> index a987661..915fc69 100644
>>> --- a/gcc/tree-pass.h
>>> +++ b/gcc/tree-pass.h
>>> @@ -498,6 +498,7 @@ extern ipa_opt_pass_d *make_pass_ipa_fn_summary
>>> (gcc::context *ctxt);
>>> extern ipa_opt_pass_d *make_pass_ipa_inline (gcc::context *ctxt);
>>> extern simple_ipa_opt_pass *make_pass_ipa_free_lang_data (gcc::context
>>> *ctxt);
>>> extern simple_ipa_opt_pass *make_pass_ipa_free_fn_summary (gcc::context
>>> *ctxt);
>>> +extern simple_ipa_opt_pass *make_pass_ipa_hello_world (gcc::context
>>> *ctxt);
>>> extern ipa_opt_pass_d *make_pass_ipa_cp (gcc::context *ctxt);
>>> extern ipa_opt_pass_d *make_pass_ipa_sra (gcc::context *ctxt);
>>> extern ipa_opt_pass_d *make_pass_ipa_icf (gcc::context *ctxt);
>>