[PATCH] D37849: [SelectionDAG] Add BITCAST handling to ComputeNumSignBits for splatted sign bits.

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: test/CodeGen/X86/bitcast-and-setcc-256.ll:380
 ; AVX12:       # BB#0:
 ; AVX12-NEXT:    vcmpltps %ymm0, %ymm1, %ymm0
 ; AVX12-NEXT:    vextractf128 $1, %ymm0, %xmm1
----------------
delena wrote:
> This code fits in 4 instructions:
> cmp
> cmp
> and
> pmovmskpd
> 
> What happens without "and", just cmp + bitcast ?
The codegen below is from the bitcast-setcc-*.ll sibling test files, there's still plenty of improvements possible with bool vectors, it's just taking a long time. D35320 should help as well of course.
```
; AVX1-LABEL: v8f32:
; AVX1:       # BB#0:
; AVX1-NEXT:    vcmpltps %ymm0, %ymm1, %ymm0
; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm1
; AVX1-NEXT:    vpacksswb %xmm1, %xmm0, %xmm0
; AVX1-NEXT:    vpshufb {{.*#+}} xmm0 = xmm0[0,2,4,6,8,10,12,14,u,u,u,u,u,u,u,u]
; AVX1-NEXT:    vpmovmskb %xmm0, %eax
; AVX1-NEXT:    # kill: %AL<def> %AL<kill> %EAX<kill>
; AVX1-NEXT:    vzeroupper
; AVX1-NEXT:    retq
;
; AVX2-LABEL: v8f32:
; AVX2:       # BB#0:
; AVX2-NEXT:    vcmpltps %ymm0, %ymm1, %ymm0
; AVX2-NEXT:    vmovmskps %ymm0, %eax
; AVX2-NEXT:    # kill: %AL<def> %AL<kill> %EAX<kill>
; AVX2-NEXT:    vzeroupper
; AVX2-NEXT:    retq
;
; AVX512-LABEL: v8f32:
; AVX512:       # BB#0:
; AVX512-NEXT:    vcmpltps %ymm0, %ymm1, %k0
; AVX512-NEXT:    kmovd %k0, %eax
; AVX512-NEXT:    # kill: %AL<def> %AL<kill> %EAX<kill>
; AVX512-NEXT:    vzeroupper
; AVX512-NEXT:    retq
  %x = fcmp ogt <8 x float> %a, %b
  %res = bitcast <8 x i1> %x to i8
  ret i8 %res
}
```


Repository:
  rL LLVM

https://reviews.llvm.org/D37849