Hi,
On Fri, 8 Jul 2011, Paulo J. Matos wrote:
> gcc4.5.3 hits continue the first time it gets there and gcc4.6.1 fails
> the inner if and enters expand_gimple_stmt twice.
Yes, the MEMREF branch merge disabled TER (temporary expression
replacement, tree-ssa-ter.c) for loads with stores that possibly alias,
because expand doesn't deal correctly with all cases.
Without TERing these two instructions expand won't see both memory
references at the same time, and hence generate separate load and store
instruction, instead of a mem-mem move if that's supported on your target
(I assume so, otherwise you wouldn't have noticed).
The question is, why doesn't combine merge the two separate load and store
insns again into one?
If you feel adventurous you can try with the below patch. Test it also
with the following testcase:
---------------------------
char str[9] = "1234";
void
bar (void)
{
unsigned int temp;
char *p = &str[2];
memcpy (&temp, &str[1], 4);
memcpy (p, &temp, 4);
}
---------------------------
If expand still has the problem and you apply the patch, then on some
targets this will emit wrong instructions because the two sides of the
MEM-MEM assignment implicitely constructed and given to expand will
partially overlap.
Ciao,
Michael.
--
Index: tree-ssa-ter.c
===================================================================
--- tree-ssa-ter.c (revision 175921)
+++ tree-ssa-ter.c (working copy)
@@ -638,6 +638,7 @@ find_replaceable_in_bb (temp_expr_table_
is a load aliasing it avoid creating overlapping
assignments which we cannot expand correctly. */
if (gimple_vdef (stmt)
+ && 0
&& gimple_assign_single_p (stmt))
{
gimple def_stmt = SSA_NAME_DEF_STMT (use);
