| Summary: | Failure to optimize vectorized conversion to `int` with AVX | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Gabriel Ravier <gabravier> |
| Component: | tree-optimization | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | NEW --- | ||
| Severity: | normal | CC: | crazylht, hjl.tools, rguenth, rsandifo |
| Priority: | P3 | Keywords: | missed-optimization |
| Version: | 11.0 | ||
| Target Milestone: | --- | ||
| Host: | Target: | x86_64-* i?86-*-* | |
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2020-08-17 00:00:00 | |
| Bug Depends on: | 36844 | ||
| Bug Blocks: | 53947 | ||
The relevant pattern is present in sse.md:
(define_insn "fix_truncv4dfv4si2<mask_name>"
[(set (match_operand:V4SI 0 "register_operand" "=v")
(fix:V4SI (match_operand:V4DF 1 "nonimmediate_operand" "vm")))]
"TARGET_AVX || (TARGET_AVX512VL && TARGET_AVX512F)"
"vcvttpd2dq{y}\t{%1, %0<mask_operand2>|%0<mask_operand2>, %1}"
but for some reason not exercised by target-independent part of the compiler.
Confirmed as a tree optimization problem.
gcc doesn't seem very fond of using 2 different vector bitsizes at the same time, so VEC_PACK_FIX_TRUNC_EXPR takes 2 vectors of 2 double and gives one vector of 4 int. At the RTL level, we have a vec_concat:V4DF of 2 V2DF adjacent in memory, but nothing knows to turn that into a single load. (the conversion itself of 4 double to int is fine) The pattern is exercised directly by BB vectorization only, loop vectorization
still uses a fixed vector size. Still the assembly shows basically the same
code when doing BB vectorization only:
f:
.LFB0:
.cfi_startproc
vmovupd (%rdi), %xmm1
vinsertf128 $0x1, 16(%rdi), %ymm1, %ymm0
vcvttpd2dqy %ymm0, %xmm0
vmovdqu %xmm0, (%rsi)
vzeroupper
ret
this is probably because of some tuning (split unaligned loads, not using
a memory operand for vcvttpd2dqy).
With -O3 -fno-tree-loop-vectorize -march=core-avx2 I get
f:
.LFB0:
.cfi_startproc
vcvttpd2dqy (%rdi), %xmm0
vmovdqu %xmm0, (%rsi)
ret
|
void f(double *src, int *dst) { for (int i = 0; i < 4; i ++) dst[i] = (int)src[i]; } With -O3 -mavx, LLVM outputs this : f(double*, int*): vcvttpd2dq xmm0, ymmword ptr [rdi] vmovupd xmmword ptr [rsi], xmm0 ret GCC outputs this : f(double*, int*): push rbp vmovupd xmm1, XMMWORD PTR [rdi] vinsertf128 ymm0, ymm1, XMMWORD PTR [rdi+16], 0x1 mov rbp, rsp vcvttpd2dq xmm0, ymm0 vmovdqu XMMWORD PTR [rsi], xmm0 vzeroupper pop rbp ret