[llvm] [X86][SelectionDAG] Handle the case for gather where index is SHL (PR #139703)

[Simon Pilgrim via llvm-commits]

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@@ -4806,18 +4806,9 @@ define <16 x float> @test_gather_structpt_16f32_mask_index(ptr %x, ptr %arr, <16
 ; X64-KNL-NEXT:    vpmovsxbd %xmm0, %zmm0
 ; X64-KNL-NEXT:    vpslld $31, %zmm0, %zmm0
 ; X64-KNL-NEXT:    vptestmd %zmm0, %zmm0, %k1
-; X64-KNL-NEXT:    vmovdqu64 (%rsi), %zmm0
-; X64-KNL-NEXT:    vpandd {{\.?LCPI[0-9]+_[0-9]+}}(%rip){1to16}, %zmm0, %zmm0
-; X64-KNL-NEXT:    vextracti64x4 $1, %zmm0, %ymm2
-; X64-KNL-NEXT:    vpmovzxdq {{.*#+}} zmm2 = ymm2[0],zero,ymm2[1],zero,ymm2[2],zero,ymm2[3],zero,ymm2[4],zero,ymm2[5],zero,ymm2[6],zero,ymm2[7],zero
-; X64-KNL-NEXT:    vpmovzxdq {{.*#+}} zmm0 = ymm0[0],zero,ymm0[1],zero,ymm0[2],zero,ymm0[3],zero,ymm0[4],zero,ymm0[5],zero,ymm0[6],zero,ymm0[7],zero
-; X64-KNL-NEXT:    vpsllq $4, %zmm0, %zmm0
-; X64-KNL-NEXT:    vpsllq $4, %zmm2, %zmm2
-; X64-KNL-NEXT:    vextractf64x4 $1, %zmm1, %ymm3
-; X64-KNL-NEXT:    kshiftrw $8, %k1, %k2
-; X64-KNL-NEXT:    vgatherqps (%rdi,%zmm2), %ymm3 {%k2}
-; X64-KNL-NEXT:    vgatherqps (%rdi,%zmm0), %ymm1 {%k1}
-; X64-KNL-NEXT:    vinsertf64x4 $1, %ymm3, %zmm1, %zmm0
+; X64-KNL-NEXT:    vpslld $4, (%rsi), %zmm0
+; X64-KNL-NEXT:    vgatherdps (%rdi,%zmm0), %zmm1 {%k1}
----------------
RKSimon wrote:

This still seems wrong - afaict you are doing this:
```
define i64 @src(i32 noundef %x) {
#0:
  %and = and i32 noundef %x, 536870911
  %zext = zext i32 %and to i64
  %hi = shl i64 %zext, 4
  ret i64 %hi
}
=>
define i64 @tgt(i32 noundef %x) {
#0:
  %shl = shl i32 noundef %x, 4
  %ext = sext i32 %shl to i64
  ret i64 %ext
}
Transformation doesn't verify!
```

https://github.com/llvm/llvm-project/pull/139703