[llvm] [SLP] Fix crash on trying to reshuffle a scalar that was vectorized. (PR #72295)

[Valery Dmitriev via llvm-commits]

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@@ -9164,7 +9164,8 @@ BoUpSLP::tryToGatherSingleRegisterExtractElements(
       continue;
     }
     auto *VecTy = dyn_cast<FixedVectorType>(EI->getVectorOperandType());
-    if (!VecTy || !isa<ConstantInt, UndefValue>(EI->getIndexOperand()))
+    if (!VecTy || !isa<ConstantInt, UndefValue>(EI->getIndexOperand()) ||
----------------
valerydmit wrote:

The problem turned out more tricky.
Slight test modification will manifest it again:
```
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/gather_extract_from_vectorbuild.ll b/llvm/test/Transforms/SLPVectorizer/X86/gather_extract_from_vectorbuild.ll
index 3bccfac8566d..4fc682488d34 100644
--- a/llvm/test/Transforms/SLPVectorizer/X86/gather_extract_from_vectorbuild.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/gather_extract_from_vectorbuild.ll
@@ -21,7 +21,7 @@ entry:

 loop:
   %ph0 = phi float [ 0.000000e+00, %entry ], [ %i4, %loop ]
-  %ph1 = phi float [ 0.000000e+00, %entry ], [ 0.000000e+00, %loop ]
+  %ph1 = phi float [ 0.000000e+00, %entry ], [ %i5, %loop ]
   %i = fadd float 0.000000e+00, %ph0
   %i1 = fadd float 0.000000e+00, %ph1
   %i2 = select i1 false, float %i, float 0.000000e+00
@@ -29,5 +29,6 @@ loop:
   %ins0 = insertelement <2 x float> zeroinitializer, float %i2, i64 0
   %ins1 = insertelement <2 x float> %ins0, float %i3, i64 1
   %i4 = extractelement <2 x float> %ins1, i64 0
+  %i5 = extractelement <2 x float> %ins1, i64 1
   br label %loop
 }
```

https://github.com/llvm/llvm-project/pull/72295