[llvm] [InstCombine] Fold shuffles through all trivially vectorizable intrinsics (PR #141979)

[Luke Lau via llvm-commits]

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@@ -264,23 +264,17 @@ define <3 x i16> @uadd_sat_v3i16(<3 x i16> %arg0, <3 x i16> %arg1) {
 ; GFX8-NEXT:  bb:
 ; GFX8-NEXT:    [[ARG0_2:%.*]] = extractelement <3 x i16> [[ARG0:%.*]], i64 2
 ; GFX8-NEXT:    [[ARG1_2:%.*]] = extractelement <3 x i16> [[ARG1:%.*]], i64 2
-; GFX8-NEXT:    [[TMP0:%.*]] = shufflevector <3 x i16> [[ARG0]], <3 x i16> poison, <2 x i32> <i32 0, i32 1>
-; GFX8-NEXT:    [[TMP1:%.*]] = shufflevector <3 x i16> [[ARG1]], <3 x i16> poison, <2 x i32> <i32 0, i32 1>
-; GFX8-NEXT:    [[TMP2:%.*]] = call <2 x i16> @llvm.uadd.sat.v2i16(<2 x i16> [[TMP0]], <2 x i16> [[TMP1]])
+; GFX8-NEXT:    [[TMP3:%.*]] = call <3 x i16> @llvm.uadd.sat.v3i16(<3 x i16> [[ARG0]], <3 x i16> [[ARG1]])
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lukel97 wrote:

Yeah it's a bit strange, but I guess that was the existing behaviour. Here's a test case in `test/InstCombine/fma.ll`:

```llvm
define <2 x float> @fma_unary_shuffle_ops_narrowing(<3 x float> %x, <3 x float> %y, <3 x float> %z) {
; CHECK-LABEL: @fma_unary_shuffle_ops_narrowing(
; CHECK-NEXT:    [[B:%.*]] = shufflevector <3 x float> [[Y:%.*]], <3 x float> poison, <2 x i32> <i32 1, i32 0>
; CHECK-NEXT:    call void @use_vec(<2 x float> [[B]])
; CHECK-NEXT:    [[TMP1:%.*]] = call nnan nsz <3 x float> @llvm.fma.v3f32(<3 x float> [[X:%.*]], <3 x float> [[Y]], <3 x float> [[Z:%.*]])
; CHECK-NEXT:    [[R:%.*]] = shufflevector <3 x float> [[TMP1]], <3 x float> poison, <2 x i32> <i32 1, i32 0>
; CHECK-NEXT:    ret <2 x float> [[R]]
;
  %a = shufflevector <3 x float> %x, <3 x float> poison, <2 x i32> <i32 1, i32 0>
  %b = shufflevector <3 x float> %y, <3 x float> poison, <2 x i32> <i32 1, i32 0>
  call void @use_vec(<2 x float> %b)
  %c = shufflevector <3 x float> %z, <3 x float> poison, <2 x i32> <i32 1, i32 0>
  %r = call nnan nsz <2 x float> @llvm.fma.v2f32(<2 x float> %a, <2 x float> %b, <2 x float> %c)
  ret <2 x float> %r
}
```

https://github.com/llvm/llvm-project/pull/141979