Hi,
When I tried to decrease # of IV candidates, I removed code that adds IV
candidates for use with constant offset stripped in use->base. This is kind of
too aggressive and triggers PR69042. So here is a patch adding back the
missing candidates. Honestly, this patch doesn't truly fix the issue, it just
brings back the original behavior in IVOPT part (Which is still a right thing
to do I think). The issue still depends on PIC_OFFSET register used on x86
target. As discussed in https://gcc.gnu.org/ml/gcc/2016-02/msg00040.html.
Furthermore, the real problem could be in register pressure modeling about
PIC_OFFSET symbol in IVOPT.
On AArch64, overall spec2k number isn't changed, though 173.applu is regressed
by ~4% because couple of loops' # of candidates now hits "--param
iv-consider-all-candidates-bound=30". For spec2k6 data on AArch64, INT is not
affected; FP overall is not changed, as for specific case: 459.GemsFDTD is
regressed by 2%, 433.milc is improved by 2%. To address the regression, I will
send another patch increasing the parameter bound.
Bootstrap&test on x86_64 and AArch64, is it OK? In the meantime, I will
collect spec2k6 data on x86_64.
Thanks,
bin
2016-03-10 Bin Cheng <bin.ch...@arm.com>
PR tree-optimization/69042
* tree-ssa-loop-ivopts.c (add_iv_candidate_for_use): Add IV cand
for use with constant offset stripped in base.
diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 4026d28..32594df 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -3232,11 +3232,13 @@ add_iv_candidate_for_use (struct ivopts_data *data,
struct iv_use *use)
basetype = sizetype;
record_common_cand (data, build_int_cst (basetype, 0), iv->step, use);
- /* Record common candidate with constant offset stripped in base. */
+ /* Record common candidate with constant offset stripped in base.
+ Like the use itself, we also add candidate directly for it. */
+ base = strip_offset (iv->base, &offset);
+ if (offset || base != iv->base)
{
- base = strip_offset (iv->base, &offset);
- if (offset || base != iv->base)
- record_common_cand (data, base, iv->step, use);
+ record_common_cand (data, base, iv->step, use);
+ add_candidate (data, base, iv->step, false, use);
}
/* Record common candidate with base_object removed in base. */
