[llvm] [ConstantFolding] Add folding for [de]interleave2, insert and extract (PR #141301)

[Yingwei Zheng via llvm-commits]

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@@ -3734,6 +3738,65 @@ static Constant *ConstantFoldFixedVectorCall(
     }
     return nullptr;
   }
+  case Intrinsic::vector_extract: {
+    auto *Vec = dyn_cast<Constant>(Operands[0]);
+    auto *Idx = dyn_cast<ConstantInt>(Operands[1]);
+    if (!Vec || !Idx)
+      return nullptr;
+
+    unsigned NumElements = FVTy->getNumElements();
+    unsigned VecNumElements =
+        cast<FixedVectorType>(Vec->getType())->getNumElements();
+    // Extracting entire vector is nop
+    if (NumElements == VecNumElements)
+      return Vec;
+
+    unsigned StartingIndex = Idx->getZExtValue();
+    assert(StartingIndex + NumElements <= VecNumElements &&
+           "Cannot extract more elements than exist in the vector");
+    for (unsigned I = 0; I != NumElements; ++I)
+      Result[I] = Vec->getAggregateElement(StartingIndex + I);
+    return ConstantVector::get(Result);
+  }
+  case Intrinsic::vector_insert: {
+    auto *Vec = dyn_cast<Constant>(Operands[0]);
+    auto *SubVec = dyn_cast<Constant>(Operands[1]);
+    auto *Idx = dyn_cast<ConstantInt>(Operands[2]);
+    if (!Vec || !SubVec || !Idx)
+      return nullptr;
+
+    unsigned SubVecNumElements =
+        cast<FixedVectorType>(SubVec->getType())->getNumElements();
+    unsigned VecNumElements =
+        cast<FixedVectorType>(Vec->getType())->getNumElements();
+    unsigned IdxN = Idx->getZExtValue();
+    // Replacing entire vector with a subvec is nop
+    if (SubVecNumElements == VecNumElements)
+      return SubVec;
+
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dtcxzyw wrote:

Return a poison vector if `IdxN + SubVecNumElements > VecNumElements`

https://github.com/llvm/llvm-project/pull/141301