[llvm] [SLP] Fix the Vec lane overridden by the shuffle mask (PR #106341)

[via llvm-commits]

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@@ -12,7 +12,7 @@ define void @test(i8 %0, i8 %1) {
 ; CHECK-NEXT:    [[TMP5:%.*]] = insertelement <16 x i8> [[TMP4]], i8 [[TMP1]], i32 1
 ; CHECK-NEXT:    [[TMP6:%.*]] = insertelement <16 x i8> [[TMP5]], i8 0, i32 7
 ; CHECK-NEXT:    [[TMP7:%.*]] = shufflevector <8 x i8> [[TMP2]], <8 x i8> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
-; CHECK-NEXT:    [[TMP8:%.*]] = shufflevector <16 x i8> [[TMP6]], <16 x i8> [[TMP7]], <16 x i32> <i32 16, i32 17, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 poison, i32 17, i32 poison, i32 poison, i32 poison, i32 poison, i32 14, i32 15>
+; CHECK-NEXT:    [[TMP8:%.*]] = shufflevector <16 x i8> [[TMP6]], <16 x i8> [[TMP7]], <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 17, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
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tcwzxx wrote:

> while it should be 0th element from %TMP2 (%li8 in the original code)

The current vectorized result is as you mentioned, but it is miscompiled.


https://github.com/llvm/llvm-project/pull/106341