c++: const void* memchr [PR113706]

The C++ standard specifies that the <string.h> functions have const and
non-const overloads, unlike C's single function with const argument and
non-const return.  Many systems don't actually implement this, but only add
an overload with non-const argument, so both end up having non-const return.
Solaris <string.h> does what the standard says, but we were penalizing it by
not recognizing the const overload as the built-in memchr.

	PR c++/113706

gcc/cp/ChangeLog:

	* decl.cc (decls_match): Handle memchr return type being
	const-qualified.

gcc/testsuite/ChangeLog:

	* g++.dg/opt/const-builtin1.C: New test.
	* c-c++-common/pr103798-2.c: Remove xfail.

3 files changed, 44 insertions, 2 deletions

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index d88e069..df85533 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -1156,6 +1156,16 @@ decls_match (tree newdecl, tree olddecl, bool record_versions /* = true */)
       tree r2 = fndecl_declared_return_type (olddecl);
       tree r1 = fndecl_declared_return_type (newdecl);
 
+      /* For memchr et al, allow const void* return type (as specified by C++)
+	 when we expect void* (as in C).  */
+      if (DECL_IS_UNDECLARED_BUILTIN (olddecl)
+	  && DECL_EXTERN_C_P (olddecl)
+	  && !same_type_p (r1, r2)
+	  && TREE_CODE (r1) == POINTER_TYPE
+	  && TREE_CODE (r2) == POINTER_TYPE
+	  && comp_ptr_ttypes (TREE_TYPE (r1), TREE_TYPE (r2)))
+	r2 = r1;
+
       tree p1 = TYPE_ARG_TYPES (f1);
       tree p2 = TYPE_ARG_TYPES (f2);
 
diff --git a/gcc/testsuite/c-c++-common/pr103798-2.c b/gcc/testsuite/c-c++-common/pr103798-2.c
index 83cdfaa..e7e99c3 100644
--- a/gcc/testsuite/c-c++-common/pr103798-2.c
+++ b/gcc/testsuite/c-c++-common/pr103798-2.c
@@ -27,5 +27,4 @@ main ()
  return 0;
 }
 
-/* See PR c++/113706 for the xfail.  */
-/* { dg-final { scan-assembler-not "memchr" { xfail { c++ && { *-*-solaris2* *-*-vxworks* } } } } } */
+/* { dg-final { scan-assembler-not "memchr" } } */
diff --git a/gcc/testsuite/g++.dg/opt/const-builtin1.C b/gcc/testsuite/g++.dg/opt/const-builtin1.C
new file mode 100644
index 0000000..8b99872
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/const-builtin1.C
@@ -0,0 +1,33 @@
+// PR c++/113706
+/* A variant of the pr103798-2.c test with const void * memchr return type, as
+   specified by the C++ standard.  */
+/* { dg-do run } */
+/* { dg-options "-O2 -fdump-tree-optimized -save-temps" } */
+
+extern "C" const void *memchr (const void *, int, __SIZE_TYPE__); // { dg-bogus "built-in" }
+
+__attribute__ ((weak))
+int
+f (int a)
+{
+   return memchr ("aE", a, 2) != 0;
+}
+
+__attribute__ ((weak))
+int
+g (char a)
+{
+  return a == 'a' || a == 'E';
+}
+
+int
+main ()
+{
+ for (int i = 0; i < 255; i++)
+   if (f (i + 256) != g (i + 256))
+     __builtin_abort ();
+
+ return 0;
+}
+
+/* { dg-final { scan-assembler-not "memchr" } } */