[PATCH] Make __PRETTY_FUNCTION__-like functions mergeable string csts (PR c++/64266).

["Martin Liška" <mliska@suse.cz>]

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Hi.

I've returned to this long-lasting issue after quite some time. Thanks to Honza I hope
I can now address the root cause which caused output of a string constant when debug info
was emitted. The problematic situation happened with following back-trace:

#0  mergeable_string_section (decl=<string_cst 0x7ffff67be210>, align=64, flags=0) at /home/marxin/Programming/gcc/gcc/varasm.c:808
#1  0x0000000001779bf3 in default_elf_select_section (decl=<string_cst 0x7ffff67be210>, reloc=0, align=64) at /home/marxin/Programming/gcc/gcc/varasm.c:6739
#2  0x000000000176efb6 in get_constant_section (exp=<string_cst 0x7ffff67be210>, align=64) at /home/marxin/Programming/gcc/gcc/varasm.c:3302
#3  0x000000000176f468 in build_constant_desc (exp=<string_cst 0x7ffff67be210>) at /home/marxin/Programming/gcc/gcc/varasm.c:3371
#4  0x000000000176f81c in output_constant_def (exp=<string_cst 0x7ffff67be210>, defer=1) at /home/marxin/Programming/gcc/gcc/varasm.c:3434
#5  0x000000000176d406 in decode_addr_const (exp=<addr_expr 0x7ffff682f8c0>, value=0x7fffffffc540) at /home/marxin/Programming/gcc/gcc/varasm.c:2951
#6  0x000000000176d93f in const_hash_1 (exp=<addr_expr 0x7ffff682f8c0>) at /home/marxin/Programming/gcc/gcc/varasm.c:3054
#7  0x000000000176fdc2 in lookup_constant_def (exp=<addr_expr 0x7ffff682f8c0>) at /home/marxin/Programming/gcc/gcc/varasm.c:3557
#8  0x0000000000dd5778 in cst_pool_loc_descr (loc=<addr_expr 0x7ffff682f8c0>) at /home/marxin/Programming/gcc/gcc/dwarf2out.c:17288

That was in situation where we emit debug info of a function that has an inlined __PRETTY_FUNCTION__ from
a different function. As seen, the constant is output due to const_hash_1 function call. Proper fix would
be to not emit these string constants for purpose of hash function.

However, I still see some minor ICEs, it's probably related to decay_conversion in cp_fname_init:

1) ./xg++ -B. /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-__func__2.C

/home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-__func__2.C:6:17: internal compiler error: Segmentation fault
6 |     [] { return __func__; }();
  |                 ^~~~~~~~
0x1344568 crash_signal
	/home/marxin/Programming/gcc/gcc/toplev.c:325
0x7ffff6bc310f ???
	/usr/src/debug/glibc-2.27-6.1.x86_64/signal/../sysdeps/unix/sysv/linux/x86_64/sigaction.c:0
0x9db134 is_capture_proxy(tree_node*)
	/home/marxin/Programming/gcc/gcc/cp/lambda.c:261
0xaeecb7 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
	/home/marxin/Programming/gcc/gcc/cp/pt.c:16700
0xaee5fd tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
	/home/marxin/Programming/gcc/gcc/cp/pt.c:16636
0xaf0ffb tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
	/home/marxin/Programming/gcc/gcc/cp/pt.c:16942

where
(gdb) p debug_tree(decl)
 <var_decl 0x7ffff7fee480 __func__
    type <pointer_type 0x7ffff69b5540
        type <integer_type 0x7ffff69b5498 char readonly unsigned string-flag type_6 QI
            size <integer_cst 0x7ffff698df78 constant 8>
            unit-size <integer_cst 0x7ffff698df90 constant 1>
            align:8 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type 0x7ffff69b5498 precision:8 min <integer_cst 0x7ffff698dfd8 0> max <integer_cst 0x7ffff698dfc0 255>
            pointer_to_this <pointer_type 0x7ffff69b5540>>
        unsigned DI
        size <integer_cst 0x7ffff698de88 constant 64>
        unit-size <integer_cst 0x7ffff698dea0 constant 8>
        align:64 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type 0x7ffff69b5540>
    readonly used tree_2 unsigned DI /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-__func__2.C:6:17 size <integer_cst 0x7ffff698de88 64> unit-size <integer_cst 0x7ffff698dea0 8>
    align:64 warn_if_not_align:0 context <function_decl 0x7ffff67abd00 operator()>
    value-expr <nop_expr 0x7ffff67b7660 type <pointer_type 0x7ffff69b5540>
        constant
        arg:0 <addr_expr 0x7ffff67b7640 type <pointer_type 0x7ffff67bd3f0>
            constant
            arg:0 <string_cst 0x7ffff67b7620 type <array_type 0x7ffff67bd348>
                constant "operator()\000">>>>

and
#0  0x00000000009db134 in is_capture_proxy (decl=<tree 0x0>) at /home/marxin/Programming/gcc/gcc/cp/lambda.c:261

2 ) ./xg++ -B. /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/ext/pretty2.C -c
/home/marxin/Programming/gcc/gcc/testsuite/g++.dg/ext/pretty2.C:16:24: internal compiler error: Segmentation fault
16 |     __PRETTY_FUNCTION__), 0))
   |                        ^
/home/marxin/Programming/gcc/gcc/testsuite/g++.dg/ext/pretty2.C:36:10: note: in expansion of macro ‘assert’
36 | int a = (assert (foo ()), 1);
   |          ^~~~~~
0x1344568 crash_signal
	/home/marxin/Programming/gcc/gcc/toplev.c:325
0x7ffff6bc310f ???
	/usr/src/debug/glibc-2.27-6.1.x86_64/signal/../sysdeps/unix/sysv/linux/x86_64/sigaction.c:0
0x9db270 is_capture_proxy(tree_node*)
	/home/marxin/Programming/gcc/gcc/cp/lambda.c:265
0x9dbad9 is_normal_capture_proxy(tree_node*)
	/home/marxin/Programming/gcc/gcc/cp/lambda.c:274
0x9c1fe6 mark_use(tree_node*, bool, bool, unsigned int, bool)
	/home/marxin/Programming/gcc/gcc/cp/expr.c:114
0x89d9ab convert_like_real
	/home/marxin/Programming/gcc/gcc/cp/call.c:6905

where:

(gdb) p debug_tree(decl)
 <var_decl 0x7ffff7fee870 __PRETTY_FUNCTION__
    type <pointer_type 0x7ffff69b4540
        type <integer_type 0x7ffff69b4498 char readonly unsigned string-flag type_6 QI
            size <integer_cst 0x7ffff698df78 constant 8>
            unit-size <integer_cst 0x7ffff698df90 constant 1>
            align:8 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type 0x7ffff69b4498 precision:8 min <integer_cst 0x7ffff698dfd8 0> max <integer_cst 0x7ffff698dfc0 255>
            pointer_to_this <pointer_type 0x7ffff69b4540>>
        unsigned type_6 DI
        size <integer_cst 0x7ffff698de88 constant 64>
        unit-size <integer_cst 0x7ffff698dea0 constant 8>
        align:64 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type 0x7ffff69b4540>
    readonly used tree_1 tree_2 unsigned read decl_6 DI /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/ext/pretty2.C:36:10 size <integer_cst 0x7ffff698de88 64> unit-size <integer_cst 0x7ffff698dea0 8>
    align:64 warn_if_not_align:0
    value-expr <nop_expr 0x7ffff67b69a0 type <pointer_type 0x7ffff69b4540>
        constant
        arg:0 <addr_expr 0x7ffff67b6980 type <pointer_type 0x7ffff67c3738>
            constant
            arg:0 <string_cst 0x7ffff67b6960 type <array_type 0x7ffff67c3690>
                constant "top level\000">>> chain <var_decl 0x7ffff7fee7e0 a>>

Can please a C++ maintainer help me with that? Having that I hope I can finish the patch.

Thank you,
Martin

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From 19db91a83ef40cbe8ca598fb397ee9a9fd8155eb Mon Sep 17 00:00:00 2001
From: marxin <mliska@suse.cz>
Date: Thu, 4 Oct 2018 15:34:51 +0200
Subject: [PATCH] Make __PRETTY_FUNCTION__-like functions mergeable string csts
 (PR c++/64266).

gcc/ChangeLog:

2018-10-22  Martin Liska  <mliska@suse.cz>

	PR c++/64266
	PR bootstrap/70422
	* varasm.c (decode_addr_const): Add new argument build.
	(const_hash_1): Set build to false by default.
	(lookup_constant_def): Do not build by default.

gcc/cp/ChangeLog:

2018-10-22  Martin Liska  <mliska@suse.cz>

	PR c++/64266
	PR bootstrap/70422
	* decl.c (cp_fname_init): Decay the initializer to pointer.
	(cp_make_fname_decl): Set DECL_DECLARED_CONSTEXPR_P,
	DECL_VALUE_EXPR, DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P.
	Don't call cp_finish_decl.
	* pt.c (tsubst_expr):  Set DECL_VALUE_EXPR,
	DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P.  Don't call cp_finish_decl.

gcc/testsuite/ChangeLog:

2018-10-22  Martin Liska  <mliska@suse.cz>

	PR c++/64266
	PR bootstrap/70422
	* g++.dg/cpp0x/constexpr-__func__2.C (main):
	(SA): Make it static assert.
	* g++.old-deja/g++.ext/pretty4.C: Remove.
---
 gcc/cp/decl.c                                 | 23 +++--
 gcc/cp/pt.c                                   | 25 +++---
 .../g++.dg/cpp0x/constexpr-__func__2.C        |  7 +-
 gcc/testsuite/g++.old-deja/g++.ext/pretty4.C  | 85 -------------------
 gcc/varasm.c                                  | 43 ++++++----
 5 files changed, 62 insertions(+), 121 deletions(-)
 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 2d9d56ef6e1..13167582266 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -4445,13 +4445,15 @@ 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;
 }
 
@@ -4474,23 +4476,34 @@ 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_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 b8b6545434b..0269fa5129a 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -16746,6 +16746,19 @@ 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;
@@ -16760,17 +16773,7 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
 						   complain, in_decl, &first,
 						   &cnt);
 
-		    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++.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 c789a03e1f3..0040f07c0e4 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -105,8 +105,8 @@ static int contains_pointers_p (tree);
 #ifdef ASM_OUTPUT_EXTERNAL
 static bool incorporeal_function_p (tree);
 #endif
-static void decode_addr_const (tree, struct addr_const *);
-static hashval_t const_hash_1 (const tree);
+static bool decode_addr_const (tree, struct addr_const *, bool build = true);
+static hashval_t const_hash_1 (const tree, bool build = true);
 static int compare_constant (const tree, const tree);
 static void output_constant_def_contents (rtx);
 static void output_addressed_constants (tree);
@@ -2877,15 +2877,17 @@ assemble_real (REAL_VALUE_TYPE d, scalar_float_mode mode, unsigned int align,
 /* Given an expression EXP with a constant value,
    reduce it to the sum of an assembler symbol and an integer.
    Store them both in the structure *VALUE.
-   EXP must be reducible.  */
+   EXP must be reducible.
+   If BUILD is false the function may fail if it is address expr of a constant
+   that is not in the constant pool.  */
 
 struct addr_const {
   rtx base;
   poly_int64 offset;
 };
 
-static void
-decode_addr_const (tree exp, struct addr_const *value)
+static bool
+decode_addr_const (tree exp, struct addr_const *value, bool build)
 {
   tree target = TREE_OPERAND (exp, 0);
   poly_int64 offset = 0;
@@ -2943,7 +2945,14 @@ decode_addr_const (tree exp, struct addr_const *value)
     case COMPLEX_CST:
     case CONSTRUCTOR:
     case INTEGER_CST:
-      x = output_constant_def (target, 1);
+      if (!build)
+	{
+	  x = lookup_constant_def (target);
+	  if (!x)
+	    return false;
+	}
+      else
+	x = output_constant_def (target, 1);
       break;
 
     case INDIRECT_REF:
@@ -2962,6 +2971,7 @@ decode_addr_const (tree exp, struct addr_const *value)
 
   value->base = x;
   value->offset = offset;
+  return true;
 }
 \f
 static GTY(()) hash_table<tree_descriptor_hasher> *const_desc_htab;
@@ -2985,7 +2995,7 @@ tree_descriptor_hasher::hash (constant_descriptor_tree *ptr)
 }
 
 static hashval_t
-const_hash_1 (const tree exp)
+const_hash_1 (const tree exp, bool build)
 {
   const char *p;
   hashval_t hi;
@@ -3014,8 +3024,8 @@ const_hash_1 (const tree exp)
       break;
 
     case COMPLEX_CST:
-      return (const_hash_1 (TREE_REALPART (exp)) * 5
-	      + const_hash_1 (TREE_IMAGPART (exp)));
+      return (const_hash_1 (TREE_REALPART (exp), build) * 5
+	      + const_hash_1 (TREE_IMAGPART (exp), build));
 
     case VECTOR_CST:
       {
@@ -3023,7 +3033,7 @@ const_hash_1 (const tree exp)
 	hi = hi * 563 + VECTOR_CST_NELTS_PER_PATTERN (exp);
 	unsigned int count = vector_cst_encoded_nelts (exp);
 	for (unsigned int i = 0; i < count; ++i)
-	  hi = hi * 563 + const_hash_1 (VECTOR_CST_ENCODED_ELT (exp, i));
+	  hi = hi * 563 + const_hash_1 (VECTOR_CST_ENCODED_ELT (exp, i), build);
 	return hi;
       }
 
@@ -3036,7 +3046,7 @@ const_hash_1 (const tree exp)
 
 	FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (exp), idx, value)
 	  if (value)
-	    hi = hi * 603 + const_hash_1 (value);
+	    hi = hi * 603 + const_hash_1 (value, build);
 
 	return hi;
       }
@@ -3046,7 +3056,8 @@ const_hash_1 (const tree exp)
       {
 	struct addr_const value;
 
-	decode_addr_const (exp, &value);
+	if (!decode_addr_const (exp, &value, build))
+	  return 0;
 	switch (GET_CODE (value.base))
 	  {
 	  case SYMBOL_REF:
@@ -3072,11 +3083,11 @@ const_hash_1 (const tree exp)
     case PLUS_EXPR:
     case POINTER_PLUS_EXPR:
     case MINUS_EXPR:
-      return (const_hash_1 (TREE_OPERAND (exp, 0)) * 9
-	      + const_hash_1 (TREE_OPERAND (exp, 1)));
+      return (const_hash_1 (TREE_OPERAND (exp, 0), build) * 9
+	      + const_hash_1 (TREE_OPERAND (exp, 1), build));
 
     CASE_CONVERT:
-      return const_hash_1 (TREE_OPERAND (exp, 0)) * 7 + 2;
+      return const_hash_1 (TREE_OPERAND (exp, 0), build) * 7 + 2;
 
     default:
       /* A language specific constant. Just hash the code.  */
@@ -3549,7 +3560,7 @@ lookup_constant_def (tree exp)
   struct constant_descriptor_tree key;
 
   key.value = exp;
-  key.hash = const_hash_1 (exp);
+  key.hash = const_hash_1 (exp, false);
   constant_descriptor_tree *desc
     = const_desc_htab->find_with_hash (&key, key.hash);
 
-- 
2.19.0