Re: [PATCH] Make __FUNCTION__ a mergeable string and do not generate symbol entry.

["Martin Liška" <mliska@suse.cz>]

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On 05/01/2017 09:13 PM, Jason Merrill wrote:
> On Wed, Apr 26, 2017 at 6:58 AM, Martin Liška <mliska@suse.cz> wrote:
>> On 04/25/2017 01:58 PM, Jakub Jelinek wrote:
>>> On Tue, Apr 25, 2017 at 01:48:05PM +0200, Martin Liška wrote:
>>>> Hello.
>>>>
>>>> This is patch that was originally installed by Jason and later reverted due to PR70422.
>>>> In the later PR Richi suggested a fix for that and Segher verified that it helped him
>>>> to survive regression tests. That's reason why I'm resending that.
>>>>
>>>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
>>>>
>>>> Ready to be installed?
>>>> Martin
>>>
>>>> >From a34ce0ef37ae00609c9f3ff98a9cb0b7db6a8bd0 Mon Sep 17 00:00:00 2001
>>>> From: marxin <mliska@suse.cz>
>>>> Date: Thu, 20 Apr 2017 14:56:30 +0200
>>>> Subject: [PATCH] Make __FUNCTION__ a mergeable string and do not generate
>>>>  symbol entry.
>>>>
>>>> gcc/cp/ChangeLog:
>>>>
>>>> 2017-04-20  Jason Merrill  <jason@redhat.com>
>>>>          Martin Liska  <mliska@suse.cz>
>>>>          Segher Boessenkool  <segher@kernel.crashing.org>
>>>>
>>>>      PR c++/64266
>>>>      PR c++/70353
>>>>      PR bootstrap/70422
>>>>      Core issue 1962
>>>>      * decl.c (cp_fname_init): Decay the initializer to pointer.
>>>>      (cp_make_fname_decl): Set DECL_DECLARED_CONSTEXPR_P,
>>>>      * pt.c (tsubst_expr) [DECL_EXPR]: Set DECL_VALUE_EXPR,
>>>>      DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P and
>>>>      DECL_IGNORED_P.  Don't call cp_finish_decl.
>>>
>>> If we don't emit those into the debug info, will the debugger be
>>> able to handle __FUNCTION__ etc. properly?
>>
>> No, debugger with the patch can't handled these. Similar to how clang
>> behaves currently. Maybe it can be conditionally enabled with -g3, or -g?
>>
>>> Admittedly, right now we emit it into debug info only if those decls
>>> are actually used, say on:
>>> const char * foo () { return __FUNCTION__; }
>>> const char * bar () { return ""; }
>>> we'd emit foo::__FUNCTION__, but not bar::__FUNCTION__, so the debugger
>>> has to have some handling of it anyway.  But while in functions
>>> that don't refer to __FUNCTION__ it is always the debugger that needs
>>> to synthetize those and thus they will be always pointer-equal,
>>> if there are some uses of it and for other uses the debugger would
>>> synthetize it, there is the possibility that the debugger synthetized
>>> string will not be the same object as actually used in the function.
>>
>> You're right, currently one has to use a special function to be able to
>> print it in debugger. I believe we've already discussed that, according
>> to spec, the strings don't have to point to a same string.
>>
>> Suggestions what we should do with the patch?
> 
> We need to emit debug information for these variables.  From Jim's
> description in 70422 it seems that the problem is that the reference
> to the string from the debug information is breaking
> function_mergeable_rodata_prefix, which relies on
> current_function_decl.  It seems to me that its callers should pass
> along their decl parameter so that f_m_r_p can use the decl's
> DECL_CONTEXT rather than rely on current_function_decl being set
> properly> 
> Jason
> 

Ok, after some time I returned back to it. I followed your advises and
changed the function function_mergeable_rodata_prefix. Apart from a small
rebase was needed.

May I ask Jim to test the patch?
Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.

Martin

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From 8a7a8b421d81c47cf686175f309f79c0b7a8ce76 Mon Sep 17 00:00:00 2001
From: marxin <mliska@suse.cz>
Date: Thu, 20 Apr 2017 14:56:30 +0200
Subject: [PATCH] Make __FUNCTION__ a mergeable string and do not generate
 symbol entry.

gcc/cp/ChangeLog:

2017-04-20  Jason Merrill  <jason@redhat.com>
	    Martin Liska  <mliska@suse.cz>
	    Segher Boessenkool  <segher@kernel.crashing.org>

	PR c++/64266
	PR c++/70353
	PR bootstrap/70422
	Core issue 1962
	* decl.c (cp_fname_init): Decay the initializer to pointer.
	(cp_make_fname_decl): Set DECL_DECLARED_CONSTEXPR_P,
	* pt.c (tsubst_expr) [DECL_EXPR]: Set DECL_VALUE_EXPR,
	DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P and
	DECL_IGNORED_P.  Don't call cp_finish_decl.
	* decl.c (cp_make_fname_decl): Add only non error mark
	expression.

gcc/testsuite/ChangeLog:

2017-04-20  Jason Merrill  <jason@redhat.com>
	    Segher Boessenkool  <segher@kernel.crashing.org>

	PR c++/64266
	PR c++/70353
	PR bootstrap/70422
	Core issue 1962
	* g++.dg/cpp0x/constexpr-__func__2.C: Add static assert test.
	* g++.dg/ext/fnname5.C: New test.
	* g++.old-deja/g++.ext/pretty4.C: Remove.

gcc/ChangeLog:

2017-07-14  Martin Liska  <mliska@suse.cz>

	* varasm.c (function_mergeable_rodata_prefix): Use DECL_CONTEXT
	for function declarations.
---
 gcc/cp/decl.c                                    | 24 +++++--
 gcc/cp/pt.c                                      | 26 +++++---
 gcc/testsuite/g++.dg/cpp0x/constexpr-__func__2.C |  7 +-
 gcc/testsuite/g++.dg/ext/fnname5.C               | 33 +++++++++
 gcc/testsuite/g++.old-deja/g++.ext/pretty4.C     | 85 ------------------------
 gcc/varasm.c                                     |  7 +-
 6 files changed, 76 insertions(+), 106 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/ext/fnname5.C
 delete mode 100644 gcc/testsuite/g++.old-deja/g++.ext/pretty4.C

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 5b8e6a22b01..3f27b72052a 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -4294,13 +4294,15 @@ cp_fname_init (const char* name, tree *type_p)
   type = cp_build_qualified_type (char_type_node, TYPE_QUAL_CONST);
   type = build_cplus_array_type (type, domain);
 
-  *type_p = type;
+  *type_p = type_decays_to (type);
 
   if (init)
     TREE_TYPE (init) = type;
   else
     init = error_mark_node;
 
+  init = decay_conversion (init, tf_warning_or_error);
+
   return init;
 }
 
@@ -4323,23 +4325,35 @@ cp_make_fname_decl (location_t loc, tree id, int type_dep)
   if (name)
     free (CONST_CAST (char *, name));
 
-  TREE_STATIC (decl) = 1;
+  /* As we're using pushdecl_with_scope, we must set the context.  */
+  DECL_CONTEXT (decl) = current_function_decl;
+
   TREE_READONLY (decl) = 1;
   DECL_ARTIFICIAL (decl) = 1;
+  DECL_IGNORED_P (decl) = 1;
+  DECL_DECLARED_CONSTEXPR_P (decl) = 1;
 
   TREE_USED (decl) = 1;
 
+  if (init)
+    {
+      SET_DECL_VALUE_EXPR (decl, init);
+      DECL_HAS_VALUE_EXPR_P (decl) = 1;
+      /* For decl_constant_var_p.  */
+      DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl) = 1;
+    }
+
   if (current_function_decl)
     {
       DECL_CONTEXT (decl) = current_function_decl;
       decl = pushdecl_outermost_localscope (decl);
-      cp_finish_decl (decl, init, /*init_const_expr_p=*/false, NULL_TREE,
-		      LOOKUP_ONLYCONVERTING);
+      if (decl != error_mark_node)
+	add_decl_expr (decl);
     }
   else
     {
       DECL_THIS_STATIC (decl) = true;
-      pushdecl_top_level_and_finish (decl, init);
+      pushdecl_top_level_and_finish (decl, NULL_TREE);
     }
 
   return decl;
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index bd02951cb85..f8e096b9b52 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -15862,21 +15862,25 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
 		    DECL_CONTEXT (decl) = current_function_decl;
 		    cp_check_omp_declare_reduction (decl);
 		  }
+		else if (VAR_P (decl)
+			 && DECL_PRETTY_FUNCTION_P (decl))
+		  {
+		    /* For __PRETTY_FUNCTION__ we have to adjust the
+		       initializer.  */
+		    const char *const name
+		      = cxx_printable_name (current_function_decl, 2);
+		    init = cp_fname_init (name, &TREE_TYPE (decl));
+		    SET_DECL_VALUE_EXPR (decl, init);
+		    DECL_HAS_VALUE_EXPR_P (decl) = 1;
+		    DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl) = 1;
+		    maybe_push_decl (decl);
+		  }
 		else
 		  {
 		    int const_init = false;
 		    maybe_push_decl (decl);
-		    if (VAR_P (decl)
-			&& DECL_PRETTY_FUNCTION_P (decl))
-		      {
-			/* For __PRETTY_FUNCTION__ we have to adjust the
-			   initializer.  */
-			const char *const name
-			  = cxx_printable_name (current_function_decl, 2);
-			init = cp_fname_init (name, &TREE_TYPE (decl));
-		      }
-		    else
-		      init = tsubst_init (init, decl, args, complain, in_decl);
+
+		    init = tsubst_init (init, decl, args, complain, in_decl);
 
 		    if (VAR_P (decl))
 		      const_init = (DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-__func__2.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-__func__2.C
index e6782905423..673fb4f3a93 100644
--- a/gcc/testsuite/g++.dg/cpp0x/constexpr-__func__2.C
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-__func__2.C
@@ -1,5 +1,5 @@
 // PR c++/70353
-// { dg-do link { target c++11 } }
+// { dg-do compile { target c++11 } }
 
 constexpr const char* ce ()
 {
@@ -8,6 +8,5 @@ constexpr const char* ce ()
 
 const char *c = ce();
 
-int main()
-{
-}
+#define SA(X) static_assert((X),#X)
+SA(ce()[0] == 'c');
diff --git a/gcc/testsuite/g++.dg/ext/fnname5.C b/gcc/testsuite/g++.dg/ext/fnname5.C
new file mode 100644
index 00000000000..04fa7d3f92d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/fnname5.C
@@ -0,0 +1,33 @@
+// PR c++/64266
+/* { dg-do compile } */
+
+extern "C" int printf (const char *, ...);
+
+struct A
+{
+  void foo(int i)
+  {
+    printf ("__FUNCTION__ = %s\n", __FUNCTION__);
+    printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
+  }
+
+  void foo()
+  {
+     printf ("__FUNCTION__ = %s\n", __FUNCTION__);
+  }
+};
+
+int
+main ()
+{
+  A a;
+  a.foo (0);
+  a.foo ();
+  return 0;
+}
+
+/* { dg-final { scan-assembler-not "_ZZN1A3fooEvE12__FUNCTION__" } } */
+/* { dg-final { scan-assembler-not "_ZZN1A3fooEiE12__FUNCTION__" } } */
+/* { dg-final { scan-assembler-not "_ZZN1A3fooEiE19__PRETTY_FUNCTION__" } } */
+/* { dg-final { scan-assembler ".(string|ascii)\\s+\"void A::foo\\(int\\)(.0)?\"" } } */
+/* { dg-final { scan-assembler ".(string|ascii)\\s+\"foo(.0)?\"" } } */
diff --git a/gcc/testsuite/g++.old-deja/g++.ext/pretty4.C b/gcc/testsuite/g++.old-deja/g++.ext/pretty4.C
deleted file mode 100644
index 9017d567132..00000000000
--- a/gcc/testsuite/g++.old-deja/g++.ext/pretty4.C
+++ /dev/null
@@ -1,85 +0,0 @@
-// { dg-do run  }
-// Copyright (C) 2000 Free Software Foundation, Inc.
-// Contributed by Nathan Sidwell 3 Mar 2000 <nathan@codesourcery.com>
-
-// __PRETTY_FUNCTION__, __FUNCTION__ and __function__ should have the
-// type char const [X], where X is the right value for that particular function
-
-static void const *strings[4];
-static void const *tpls[4];
-static unsigned pos = 0;
-static int fail;
-static void const *ptr = 0;
-
-void unover (char const (*)[5]) {}
-void foo (char const (*)[5]) {}
-void foo (void *) {fail = 1;}
-void foo (void const *) {fail = 1;}
-void baz (char const (&)[5]) {}
-
-template<unsigned I> void PV (char const (&objRef)[I])
-{
-  strings[pos] = objRef;
-  tpls[pos] = __PRETTY_FUNCTION__;
-  pos++;
-}
-
-void fn ()
-{
-  PV (__FUNCTION__);
-  PV (__func__);
-  PV (__PRETTY_FUNCTION__);
-  PV ("wibble");
-}
-
-void baz ()
-{
-  ptr = __FUNCTION__;
-  // there should be no string const merging
-  if (ptr == "baz")
-    fail = 1;
-  // but all uses should be the same.
-  if (ptr != __FUNCTION__)
-    fail = 1;
-}
-int baz (int)
-{
-  return ptr == __FUNCTION__;
-}
-
-int main ()
-{
-  // make sure we actually emit the VAR_DECL when needed, and things have the
-  // expected type.
-  foo (&__FUNCTION__);
-  baz (__FUNCTION__);
-  unover (&__FUNCTION__);
-  if (fail)
-    return 1;
-  
-  // __FUNCTION__ should be unique across functions with the same base name
-  // (it's a local static, _not_ a string).
-  baz ();
-  if (fail)
-    return 1;
-  if (baz (1))
-    return 1;
-  fn ();
-  
-  // Check the names of fn. They should all be distinct strings (though two
-  // will have the same value).
-  if (strings[0] == strings[1])
-    return 1;
-  if (strings[0] == strings[2])
-    return 1;
-  if (strings[1] == strings[2])
-    return 1;
-
-  // check the names of the template functions so invoked
-  if (tpls[0] != tpls[1])
-    return 1;
-  if (tpls[0] == tpls[2])
-    return 1;
-  
-  return 0;
-}
diff --git a/gcc/varasm.c b/gcc/varasm.c
index fbaebc1b5c0..0b56898d8f3 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -760,7 +760,12 @@ default_no_function_rodata_section (tree decl ATTRIBUTE_UNUSED)
 static const char *
 function_mergeable_rodata_prefix (void)
 {
-  section *s = targetm.asm_out.function_rodata_section (current_function_decl);
+  tree decl = current_function_decl;
+  if (decl && DECL_CONTEXT (decl)
+      && TREE_CODE (DECL_CONTEXT (decl)) == FUNCTION_DECL)
+    decl = DECL_CONTEXT (decl);
+
+  section *s = targetm.asm_out.function_rodata_section (decl);
   if (SECTION_STYLE (s) == SECTION_NAMED)
     return s->named.name;
   else
-- 
2.13.2