https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115517
--- Comment #4 from Hongtao Liu <liuhongt at gcc dot gnu.org> --- (In reply to rguent...@suse.de from comment #3) > On Tue, 18 Jun 2024, liuhongt at gcc dot gnu.org wrote: > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115517 > > > > --- Comment #2 from Hongtao Liu <liuhongt at gcc dot gnu.org> --- > > (In reply to Richard Biener from comment #1) > > > Btw, I had opened PR115490 with my results for this already. Some > > > mitigation > > > should be from optimizing ISEL expansion to vcond_mask and I'd start with > > > looking at some of the fallout from that side (note that might require > > > the backend reject not natively implemented vec_cmp via its operand 1 > > > predicate) > > > > w/o AVX512, vector integer comparison only supports EQ/GT, others comparison > > rtx_cost is transformed to that. (.i.e GTU is emulated with us_minus + eq + > > negative the vector mask) > > If we restrict the predicate of operand 1, would middle-end reject > > vectorization (or lower it to scalar version)? > > Richard suggests that we implement the "obvious" transforms like > inversion in the middle-end but if for example unsigned compares > are not supported the us_minus + eq + negative trick isn't on > that list. > > The main reason to restrict vec_cmp would be to avoid > a <= b ? c : d going with an unsupported vec_cmp but instead > do a > b ? d : c - the alternative is trying to fix this > on the RTL side via combine. I understand the non-native Yes, I have a patch which can fix most regressions via pattern match in combine. Still there is a situation that is difficult to deal with, mainly the optimization w/o sse4.1 . Because pblendvb/blendvps/blendvpd only exists under sse4.1, w/o sse4.1, it takes 3 instructions (pand,pandn,por) to simulate the vcond_mask, and the combine matches up to 4 instructions, which makes it currently impossible to use the combine to recover those optimizations in the vcond{,u,eq}.i.e min/max. In the case of sse 4.1 and above, there is basically no regression anymore. the regression testcases w/o sse4.1 FAIL: g++.target/i386/pr100637-1b.C -std=gnu++14 scan-assembler-times pcmpeqb 2 FAIL: g++.target/i386/pr100637-1b.C -std=gnu++17 scan-assembler-times pcmpeqb 2 FAIL: g++.target/i386/pr100637-1b.C -std=gnu++20 scan-assembler-times pcmpeqb 2 FAIL: g++.target/i386/pr100637-1b.C -std=gnu++98 scan-assembler-times pcmpeqb 2 FAIL: g++.target/i386/pr100637-1w.C -std=gnu++14 scan-assembler-times pcmpeqw 2 FAIL: g++.target/i386/pr100637-1w.C -std=gnu++17 scan-assembler-times pcmpeqw 2 FAIL: g++.target/i386/pr100637-1w.C -std=gnu++20 scan-assembler-times pcmpeqw 2 FAIL: g++.target/i386/pr100637-1w.C -std=gnu++98 scan-assembler-times pcmpeqw 2 FAIL: g++.target/i386/pr103861-1.C -std=gnu++14 scan-assembler-times pcmpeqb 2 FAIL: g++.target/i386/pr103861-1.C -std=gnu++17 scan-assembler-times pcmpeqb 2 FAIL: g++.target/i386/pr103861-1.C -std=gnu++20 scan-assembler-times pcmpeqb 2 FAIL: g++.target/i386/pr103861-1.C -std=gnu++98 scan-assembler-times pcmpeqb 2 FAIL: gcc.target/i386/pr88540.c scan-assembler minpd
