On Tue, Sep 11, 2018 at 04:06:40PM +0200, Andreas Krebbel wrote:
> > It is a fix, but not optimal.
> > We have essentially:
> > MEM[(int *)p_28] = 0;
> > MEM[(char *)p_28 + 3B] = 1;
> > MEM[(char *)p_28 + 1B] = 2;
> > MEM[(char *)p_28 + 2B] = MEM[(char *)p_28 + 6B];
> > It is useful to merge the first 3 stores into:
> > MEM[(int *)p_28] = 0x01000200; // or 0x00020001; depending on endianity
> > MEM[(char *)p_28 + 2B] = MEM[(char *)p_28 + 6B];
> > rather than punt, and just ignore (i.e. make sure it isn't merged with
> > anything else) the non-INTEGER_CST store). If you don't mind, I'll take
> > this
> > PR over and handle it tomorrow.
>
> Please do. Thanks!
Here it is, I hope the added comments are clear enough on what's going on
and when we can and when we can't handle it.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk and
eventually 8.3?
2018-09-12 Jakub Jelinek <ja...@redhat.com>
Andreas Krebbel <kreb...@linux.ibm.com>
PR tree-optimization/86844
* gimple-ssa-store-merging.c
(imm_store_chain_info::coalesce_immediate): For overlapping stores, if
there are any overlapping stores in between them, make sure they are
also coalesced or we give up completely.
* gcc.c-torture/execute/pr86844.c: New test.
* gcc.dg/store_merging_22.c: New test.
* gcc.dg/store_merging_23.c: New test.
--- gcc/gimple-ssa-store-merging.c.jj 2018-07-12 09:38:46.137335036 +0200
+++ gcc/gimple-ssa-store-merging.c 2018-09-11 22:47:41.406582798 +0200
@@ -2702,15 +2702,80 @@ imm_store_chain_info::coalesce_immediate
{
/* Only allow overlapping stores of constants. */
if (info->rhs_code == INTEGER_CST
- && merged_store->stores[0]->rhs_code == INTEGER_CST
- && check_no_overlap (m_store_info, i, INTEGER_CST,
- MAX (merged_store->last_order, info->order),
- MAX (merged_store->start
- + merged_store->width,
- info->bitpos + info->bitsize)))
+ && merged_store->stores[0]->rhs_code == INTEGER_CST)
{
- merged_store->merge_overlapping (info);
- goto done;
+ unsigned int last_order
+ = MAX (merged_store->last_order, info->order);
+ unsigned HOST_WIDE_INT end
+ = MAX (merged_store->start + merged_store->width,
+ info->bitpos + info->bitsize);
+ if (check_no_overlap (m_store_info, i, INTEGER_CST,
+ last_order, end))
+ {
+ /* check_no_overlap call above made sure there are no
+ overlapping stores with non-INTEGER_CST rhs_code
+ in between the first and last of the stores we've
+ just merged. If there are any INTEGER_CST rhs_code
+ stores in between, we need to merge_overlapping them
+ even if in the sort_by_bitpos order there are other
+ overlapping stores in between. Keep those stores as is.
+ Example:
+ MEM[(int *)p_28] = 0;
+ MEM[(char *)p_28 + 3B] = 1;
+ MEM[(char *)p_28 + 1B] = 2;
+ MEM[(char *)p_28 + 2B] = MEM[(char *)p_28 + 6B];
+ We can't merge the zero store with the store of two and
+ not merge anything else, because the store of one is
+ in the original order in between those two, but in
+ store_by_bitpos order it comes after the last store that
+ we can't merge with them. We can merge the first 3 stores
+ and keep the last store as is though. */
+ unsigned int len = m_store_info.length (), k = i;
+ for (unsigned int j = i + 1; j < len; ++j)
+ {
+ store_immediate_info *info2 = m_store_info[j];
+ if (info2->bitpos >= end)
+ break;
+ if (info2->order < last_order)
+ {
+ if (info2->rhs_code != INTEGER_CST)
+ {
+ /* Normally check_no_overlap makes sure this
+ doesn't happen, but if end grows below, then
+ we need to process more stores than
+ check_no_overlap verified. Example:
+ MEM[(int *)p_5] = 0;
+ MEM[(short *)p_5 + 3B] = 1;
+ MEM[(char *)p_5 + 4B] = _9;
+ MEM[(char *)p_5 + 2B] = 2; */
+ k = 0;
+ break;
+ }
+ k = j;
+ end = MAX (end, info2->bitpos + info2->bitsize);
+ }
+ }
+
+ if (k != 0)
+ {
+ merged_store->merge_overlapping (info);
+
+ for (unsigned int j = i + 1; j <= k; j++)
+ {
+ store_immediate_info *info2 = m_store_info[j];
+ gcc_assert (info2->bitpos < end);
+ if (info2->order < last_order)
+ {
+ gcc_assert (info2->rhs_code == INTEGER_CST);
+ merged_store->merge_overlapping (info2);
+ }
+ /* Other stores are kept and not merged in any
+ way. */
+ }
+ ignore = k;
+ goto done;
+ }
+ }
}
}
/* |---store 1---||---store 2---|
--- gcc/testsuite/gcc.c-torture/execute/pr86844.c.jj 2018-09-11
18:25:16.882452028 +0200
+++ gcc/testsuite/gcc.c-torture/execute/pr86844.c 2018-09-11
18:25:16.882452028 +0200
@@ -0,0 +1,24 @@
+/* PR tree-optimization/86844 */
+
+__attribute__((noipa)) void
+foo (int *p)
+{
+ *p = 0;
+ *((char *)p + 3) = 1;
+ *((char *)p + 1) = 2;
+ *((char *)p + 2) = *((char *)p + 6);
+}
+
+int
+main ()
+{
+ int a[2] = { -1, 0 };
+ if (sizeof (int) != 4)
+ return 0;
+ ((char *)a)[6] = 3;
+ foo (a);
+ if (((char *)a)[0] != 0 || ((char *)a)[1] != 2
+ || ((char *)a)[2] != 3 || ((char *)a)[3] != 1)
+ __builtin_abort ();
+ return 0;
+}
--- gcc/testsuite/gcc.dg/store_merging_22.c.jj 2018-09-12 10:14:34.286704682
+0200
+++ gcc/testsuite/gcc.dg/store_merging_22.c 2018-09-12 10:25:30.156727153
+0200
@@ -0,0 +1,16 @@
+/* PR tree-optimization/86844 */
+/* { dg-do compile } */
+/* { dg-require-effective-target store_merge } */
+/* { dg-options "-O2 -fdump-tree-store-merging" } */
+
+void
+foo (int *p)
+{
+ *p = 0;
+ *((char *)p + 3) = 1;
+ *((char *)p + 1) = 2;
+ *((char *)p + 2) = *((char *)p + 38);
+}
+
+/* { dg-final { scan-tree-dump-times "Merging successful" 1 "store-merging" }
} */
+/* { dg-final { scan-tree-dump-times "New sequence of 1 stores to replace old
one of 3 stores" 1 "store-merging" } } */
--- gcc/testsuite/gcc.dg/store_merging_23.c.jj 2018-09-12 10:25:41.099544995
+0200
+++ gcc/testsuite/gcc.dg/store_merging_23.c 2018-09-12 10:32:27.956772277
+0200
@@ -0,0 +1,16 @@
+/* PR tree-optimization/86844 */
+/* { dg-do compile } */
+/* { dg-require-effective-target store_merge } */
+/* { dg-options "-O2 -fdump-tree-store-merging" } */
+
+void
+foo (int *p)
+{
+ *p = 0;
+ int one = 1;
+ __builtin_memcpy ((char *) p + 3, &one, sizeof (int));
+ *((char *)p + 4) = *((char *)p + 36);
+ *((char *)p + 1) = 2;
+}
+
+/* { dg-final { scan-tree-dump-not "Merging successful" "store-merging" } } */
Jakub
