At one time I know I had the max_size == size test in
valid_ao_ref_for_dse. But it got lost at some point. This is what
caused the Ada failure.
Technically it'd be OK for the potentially dead store to have a variable
size as long as the later stores covered the entire range of the
potentially dead store. I doubt this happens enough to be worth checking.
The ppc64 big endian failures were more interesting. We had this in the IL:
memmove (dst, src, 0)
The trimming code assumes that there's at least one live byte in the
store, which obviously isn't the case here. The net result is we
compute an incorrect trim and the copy goes wild with incorrect
addresses and lengths. This is trivial to fix by validating that the
store has a nonzero length.
I was a bit curious how often this happened in practice because such a
call is trivially dead. ~80 during a bootstrap and a few dozen in the
testsuite. Given how trivial it is to detect and optimize, this patch
includes removal of such calls. This hunk makes the check for zero size
in valid_ao_ref_for_dse redundant, but I'd like to keep the check -- if
we add more builtin support without filtering zero size we'd regress again.
I wanted to get this in tonight given the Ada and ppc64 breakage so I
didn't do testcase reductions for the ppc test or the zero length
optimization (acats covers the Ada breakage). I'll get testcases done
Monday. I'll also finish generating suitable baselines for
ppc64-linux-gnu over the rest of the weekend to verify if this fixes all
the ppc64 regressions or just a subset of them.
Bootstrapped on x86_64-linux-gnu and ppc64-linux-gnu. Regression tested
on x86_64-linux-gnu. Also verified the ppc64 testresults are improved
(anything where sel-sched was faulting ought to be fixed now, maybe
others). Installing on the trunk.
Jeff
commit 04c5d9cab65e2f5b219f9610621bea06173b9cb8
Author: Jeff Law <l...@redhat.com>
Date: Sun Jan 15 01:37:32 2017 -0700
PR tree-optimization/79090
* tree-ssa-dse.c (valid_ao_ref_for_dse): Reject zero length and
variable length stores.
(compute_trims): Delete dead assignment to *trim_tail.
(dse_dom_walker::dse_optimize_stmt): Optimize mem* calls with
zero length.
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 746f6af..36982c6 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2017-01-14 Jeff Law <l...@redhat.com>
+
+ PR tree-optimization/79090
+ * tree-ssa-dse.c (valid_ao_ref_for_dse): Reject zero length and
+ variable length stores.
+ (compute_trims): Delete dead assignment to *trim_tail.
+ (dse_dom_walker::dse_optimize_stmt): Optimize mem* calls with
+ zero length.
+
2017-01-14 Bernd Schmidt <bschm...@redhat.com>
PR rtl-optimization/78626
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index 2e6f8ff..65dcb12 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -129,6 +129,8 @@ valid_ao_ref_for_dse (ao_ref *ref)
{
return (ao_ref_base (ref)
&& ref->max_size != -1
+ && ref->size != 0
+ && ref->max_size == ref->size
&& (ref->offset % BITS_PER_UNIT) == 0
&& (ref->size % BITS_PER_UNIT) == 0
&& (ref->size != -1));
@@ -221,7 +223,6 @@ compute_trims (ao_ref *ref, sbitmap live, int *trim_head,
int *trim_tail)
the REF to compute the trims. */
/* Now identify how much, if any of the tail we can chop off. */
- *trim_tail = 0;
int last_orig = (ref->size / BITS_PER_UNIT) - 1;
int last_live = bitmap_last_set_bit (live);
*trim_tail = (last_orig - last_live) & ~0x1;
@@ -700,6 +701,16 @@ dse_dom_walker::dse_optimize_stmt (gimple_stmt_iterator
*gsi)
case BUILT_IN_MEMMOVE:
case BUILT_IN_MEMSET:
{
+ /* Occasionally calls with an explicit length of zero
+ show up in the IL. It's pointless to do analysis
+ on them, they're trivially dead. */
+ tree size = gimple_call_arg (stmt, 2);
+ if (integer_zerop (size))
+ {
+ delete_dead_call (gsi);
+ return;
+ }
+
gimple *use_stmt;
enum dse_store_status store_status;
m_byte_tracking_enabled
