[llvm] [SLP][REVEC] The vectorized result for ShuffleVector may not be ShuffleVectorInst. (PR #116940)

[Han-Kuan Chen via llvm-commits]

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@@ -15713,16 +15713,19 @@ Value *BoUpSLP::vectorizeTree(TreeEntry *E, bool PostponedPHIs) {
           LLVM_DEBUG(dbgs() << "SLP: Diamond merged for " << *VL0 << ".\n");
           return E->VectorizedValue;
         }
-        assert(isa<ShuffleVectorInst>(Src) &&
-               "Not supported shufflevector usage.");
-        auto *SVSrc = cast<ShuffleVectorInst>(Src);
-        assert(isa<PoisonValue>(SVSrc->getOperand(1)) &&
-               "Not supported shufflevector usage.");
         SmallVector<int> ThisMask(calculateShufflevectorMask(E->Scalars));
-        SmallVector<int> NewMask(ThisMask.size());
-        transform(ThisMask, NewMask.begin(),
-                  [&SVSrc](int Mask) { return SVSrc->getShuffleMask()[Mask]; });
-        V = Builder.CreateShuffleVector(SVSrc->getOperand(0), NewMask);
+        if (isa<ShuffleVectorInst>(Src)) {
+          auto *SVSrc = cast<ShuffleVectorInst>(Src);
+          assert(isa<PoisonValue>(SVSrc->getOperand(1)) &&
+                 "Not supported shufflevector usage.");
+          SmallVector<int> NewMask(ThisMask.size());
+          transform(ThisMask, NewMask.begin(), [&SVSrc](int Mask) {
+            return SVSrc->getShuffleMask()[Mask];
+          });
+          V = Builder.CreateShuffleVector(SVSrc->getOperand(0), NewMask);
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HanKuanChen wrote:

No. `SVSrc` has its own mask. But the current shufflevector has its own mask (from `calculateShufflevectorMask(E->Scalars)`) too. We are trying to blend the mask from `calculateShufflevectorMask` and `SVSrc`.

https://github.com/llvm/llvm-project/pull/116940