On Thu, Jul 13, 2023 at 6:45 PM Roger Sayle <ro...@nextmovesoftware.com> wrote:
>
>
> This is the next piece towards a fix for (the x86_64 ABI issues affecting)
> PR 88873. This patch generalizes the recent tweak to ix86_expand_move
> for setting the highpart of a TImode reg from a DImode source using
> *insvti_highpart_1, to handle both DImode and DFmode sources, and also
> use the recently added *insvti_lowpart_1 for setting the lowpart.
>
> Although this is another intermediate step (not yet a fix), towards
> enabling *insvti and *concat* patterns to be candidates for TImode STV
> (by using V2DI/V2DF instructions), it already improves things a little.
>
> For the test case from PR 88873
>
> typedef struct { double x, y; } s_t;
> typedef double v2df __attribute__ ((vector_size (2 * sizeof(double))));
>
> s_t foo (s_t a, s_t b, s_t c)
> {
> return (s_t) { fma(a.x, b.x, c.x), fma (a.y, b.y, c.y) };
> }
>
>
> With -O2 -march=cascadelake, GCC currently generates:
>
> Before (29 instructions):
> vmovq %xmm2, -56(%rsp)
> movq -56(%rsp), %rdx
> vmovq %xmm4, -40(%rsp)
> movq $0, -48(%rsp)
> movq %rdx, -56(%rsp)
> movq -40(%rsp), %rdx
> vmovq %xmm0, -24(%rsp)
> movq %rdx, -40(%rsp)
> movq -24(%rsp), %rsi
> movq -56(%rsp), %rax
> movq $0, -32(%rsp)
> vmovq %xmm3, -48(%rsp)
> movq -48(%rsp), %rcx
> vmovq %xmm5, -32(%rsp)
> vmovq %rax, %xmm6
> movq -40(%rsp), %rax
> movq $0, -16(%rsp)
> movq %rsi, -24(%rsp)
> movq -32(%rsp), %rsi
> vpinsrq $1, %rcx, %xmm6, %xmm6
> vmovq %rax, %xmm7
> vmovq %xmm1, -16(%rsp)
> vmovapd %xmm6, %xmm3
> vpinsrq $1, %rsi, %xmm7, %xmm7
> vfmadd132pd -24(%rsp), %xmm7, %xmm3
> vmovapd %xmm3, -56(%rsp)
> vmovsd -48(%rsp), %xmm1
> vmovsd -56(%rsp), %xmm0
> ret
>
> After (20 instructions):
> vmovq %xmm2, -56(%rsp)
> movq -56(%rsp), %rax
> vmovq %xmm3, -48(%rsp)
> vmovq %xmm4, -40(%rsp)
> movq -48(%rsp), %rcx
> vmovq %xmm5, -32(%rsp)
> vmovq %rax, %xmm6
> movq -40(%rsp), %rax
> movq -32(%rsp), %rsi
> vpinsrq $1, %rcx, %xmm6, %xmm6
> vmovq %xmm0, -24(%rsp)
> vmovq %rax, %xmm7
> vmovq %xmm1, -16(%rsp)
> vmovapd %xmm6, %xmm2
> vpinsrq $1, %rsi, %xmm7, %xmm7
> vfmadd132pd -24(%rsp), %xmm7, %xmm2
> vmovapd %xmm2, -56(%rsp)
> vmovsd -48(%rsp), %xmm1
> vmovsd -56(%rsp), %xmm0
> ret
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-m32}
> with no new failures. No testcase yet, as the above code will hopefully
> change dramatically with the next pieces. Ok for mainline?
>
>
> 2023-07-13 Roger Sayle <ro...@nextmovesoftware.com>
>
> gcc/ChangeLog
> * config/i386/i386-expand.cc (ix86_expand_move): Generalize special
> case inserting of 64-bit values into a TImode register, to handle
> both DImode and DFmode using either *insvti_lowpart_1
> or *isnvti_highpart_1.
LGTM, but please watch out for fallout.
Thanks,
Uros.
