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Re: C++ PATCH for c++/39480

Ian Lance Taylor wrote:
The chance of this logic remaining in sync over time seems rather low,
especially since the code is in two different directories.  I think that
on mainline the condition, trivial as it is, ought to move into a
function in builtins.c.  I'll preapprove the patch to builtins.c.

I was planning to remove the call to builtin_memcpy entirely for 4.5. If you still want the separate function, were you thinking something like this?


commit 2574a0ce946df86e72226840f333f9f9ae227317
Author: Jason Merrill <>
Date:   Wed Apr 15 17:35:11 2009 -0400

diff --git a/gcc/builtins.c b/gcc/builtins.c
index 9f0f4ac..00ee77a 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -341,6 +341,16 @@ get_object_alignment (tree exp, unsigned int align, unsigned int max_align)
   return MIN (align, max_align);
+/* Returns true iff we can trust that alignment information has been
+   calculated properly.  */
+can_trust_pointer_alignment (void)
+  /* We rely on TER to compute accurate alignment information.  */
+  return (optimize && flag_tree_ter);
 /* Return the alignment in bits of EXP, a pointer valued expression.
    But don't return more than MAX_ALIGN no matter what.
    The alignment returned is, by default, the alignment of the thing that
@@ -354,8 +364,7 @@ get_pointer_alignment (tree exp, unsigned int max_align)
   unsigned int align, inner;
-  /* We rely on TER to compute accurate alignment information.  */
-  if (!(optimize && flag_tree_ter))
+  if (!can_trust_pointer_alignment ())
     return 0;
   if (!POINTER_TYPE_P (TREE_TYPE (exp)))
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index ef7c045..0e53095 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -5402,11 +5402,11 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 	  arg1 = arg;
 	  arg0 = cp_build_unary_op (ADDR_EXPR, to, 0, complain);
-	  if (!(optimize && flag_tree_ter))
+	  if (!can_trust_pointer_alignment ())
-	      /* When TER is off get_pointer_alignment returns 0, so a call
+	      /* If we can't be sure about pointer alignment, a call
 		 to __builtin_memcpy is expanded as a call to memcpy, which
-		 is invalid with identical args.  When TER is on it is
+		 is invalid with identical args.  Otherwise it is
 		 expanded as a block move, which should be safe.  */
 	      arg0 = save_expr (arg0);
 	      arg1 = save_expr (arg1);
diff --git a/gcc/tree.h b/gcc/tree.h
index b191d43..e1865c2 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -4838,6 +4838,7 @@ extern tree build_va_arg_indirect_ref (tree);
 extern tree build_string_literal (int, const char *);
 extern bool validate_arglist (const_tree, ...);
 extern rtx builtin_memset_read_str (void *, HOST_WIDE_INT, enum machine_mode);
+extern bool can_trust_pointer_alignment (void);
 extern int get_pointer_alignment (tree, unsigned int);
 extern bool is_builtin_name(const char*);
 extern int get_object_alignment (tree, unsigned int, unsigned int);

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