http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56151
Steven Bosscher <steven at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |steven at gcc dot gnu.org
--- Comment #4 from Steven Bosscher <steven at gcc dot gnu.org> 2013-02-03
01:05:34 UTC ---
Patch to help explain the problem:
Index: optabs.c
===================================================================
--- optabs.c (revision 195687)
+++ optabs.c (working copy)
@@ -1452,8 +1452,13 @@ expand_binop_directly (enum machine_mode
{
/* If PAT is composed of more than one insn, try to add an appropriate
REG_EQUAL note to it. If we can't because TEMP conflicts with an
- operand, call expand_binop again, this time without a target. */
+ operand, call expand_binop again, this time without a target.
+
+ However, if target is a MEM, just accept the lossage of not having
+ a REG_EQUAL note. This avoids splitting up insns of the form
+ "MEM=MEM op X", a form we may not be able to reconstruct later. */
if (INSN_P (pat) && NEXT_INSN (pat) != NULL_RTX
+ && ! (target && MEM_P (target))
&& ! add_equal_note (pat, ops[0].value, optab_to_code (binoptab),
ops[1].value, ops[2].value))
{
