> Emulated gather/scatter behave similar to strided elementwise > accesses in that they need to decompose the offset vector > and construct or decompose the data vector so handle them > the same way, pessimizing the cases with may elements. > > For pr88531-2c.c instead of > > .L4: > leaq (%r15,%rcx), %rdx > incl %edi > movl 16(%rdx), %r13d > movl 24(%rdx), %r14d > movl (%rdx), %r10d > movl 4(%rdx), %r9d > movl 8(%rdx), %ebx > movl 12(%rdx), %r11d > movl 20(%rdx), %r12d > vmovss (%rax,%r14,4), %xmm2 > movl 28(%rdx), %edx > vmovss (%rax,%r13,4), %xmm1 > vmovss (%rax,%r10,4), %xmm0 > vinsertps $0x10, (%rax,%rdx,4), %xmm2, %xmm2 > vinsertps $0x10, (%rax,%r12,4), %xmm1, %xmm1 > vinsertps $0x10, (%rax,%r9,4), %xmm0, %xmm0 > vmovlhps %xmm2, %xmm1, %xmm1 > vmovss (%rax,%rbx,4), %xmm2 > vinsertps $0x10, (%rax,%r11,4), %xmm2, %xmm2 > vmovlhps %xmm2, %xmm0, %xmm0 > vinsertf128 $0x1, %xmm1, %ymm0, %ymm0 > vmulps %ymm3, %ymm0, %ymm0 > vmovups %ymm0, (%r8,%rcx) > addq $32, %rcx > cmpl %esi, %edi > jb .L4 > > we now prefer > > .L4: > leaq 0(%rbp,%rdx,8), %rcx > movl (%rcx), %r10d > movl 4(%rcx), %ecx > vmovss (%rsi,%r10,4), %xmm0 > vinsertps $0x10, (%rsi,%rcx,4), %xmm0, %xmm0 > vmulps %xmm1, %xmm0, %xmm0 > vmovlps %xmm0, (%rbx,%rdx,8) > incq %rdx > cmpl %edi, %edx > jb .L4 > > which vectorizes with SSE instead of AVX2 which looks like an > improvement. > > When testing this on SPEC CPU 2017 with -Ofast -flto -march=znver4 > there are quite some cases where we now prefer SSE vectorization > over AVX512 + AVX2 epilogue and some cases where we now reject > vectorization. Runtime the changes are noise with the off-noise > candidates better after the patch. > > Bootstrapped and tested on x86_64-unknown-linux-gnu. > > OK for stage1? > > Thanks, > Richard. > > * config/i386/i386.cc (ix86_vector_costs::add_stmt_cost): > Tame down element extracts and scalar loads for gather/scatter > similar to elementwise strided accesses. > > * gcc.target/i386/pr89618-2.c: New testcase. > * gcc.target/i386/pr88531-2b.c: Adjust. > * gcc.target/i386/pr88531-2c.c: Likewise. OK.
Honza
