> -----Original Message----- > From: Andre Vieira (lists) <andre.simoesdiasvie...@arm.com> > Sent: 03 February 2021 17:59 > To: gcc-patches@gcc.gnu.org > Cc: Kyrylo Tkachov <kyrylo.tkac...@arm.com> > Subject: [AArch64] Fix vector multiplication costs > > This patch introduces a vect.mul RTX cost and decouples the vector > multiplication costing from the scalar one. > > After Wilco's "AArch64: Add cost table for Cortex-A76" patch we saw a > regression in vector codegen. Reproduceable with the small test added in > this patch. > Upon further investigation we noticed 'aarch64_rtx_mult_cost' was using > scalar costs to calculate the cost of vector multiplication, which was > now lower and preventing 'choose_mult_variant' from making the right > choice to expand such vector multiplications with constants as shift and > sub's. I also added a special case for SSRA to use the default vector > cost rather than mult, SSRA seems to be cost using > 'aarch64_rtx_mult_cost', which to be fair is quite curious. I believe we > should have a better look at 'aarch64_rtx_costs' altogether and > completely decouple vector and scalar costs. Though that is something > that requires more rewriting than I believe should be done in Stage 4. > > I gave all targets a vect.mult cost of 4x the vect.alu cost, with the > exception of targets with cost 0 for vect.alu, those I gave the cost 4. > > Bootstrapped on aarch64. > > Is this OK for trunk?
Ok. Thanks, Kyrill > > gcc/ChangeLog: > > * config/aarch64/aarch64-cost-tables.h: Add entries for vect.mul. > * config/aarch64/aarch64.c (aarch64_rtx_mult_cost): Use > vect.mul for > vector multiplies and vect.alu for SSRA. > * config/arm/aarch-common-protos.h (struct vector_cost_table): > Define > vect.mul cost field. > * config/arm/aarch-cost-tables.h: Add entries for vect.mul. > * config/arm/arm.c: Likewise. > > gcc/testsuite/ChangeLog: > > * gcc.target/aarch64/asimd-mul-to-shl-sub.c: New test.
