[clang] [CIR] Implement folder for VecShuffleDynamicOp (PR #142315)

[Amr Hesham via cfe-commits]

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@@ -1579,6 +1579,38 @@ OpFoldResult cir::VecExtractOp::fold(FoldAdaptor adaptor) {
 // VecShuffleDynamicOp
 //===----------------------------------------------------------------------===//
 
+OpFoldResult cir::VecShuffleDynamicOp::fold(FoldAdaptor adaptor) {
+  mlir::Attribute vec = adaptor.getVec();
+  mlir::Attribute indices = adaptor.getIndices();
+  if (mlir::isa_and_nonnull<cir::ConstVectorAttr>(vec) &&
+      mlir::isa_and_nonnull<cir::ConstVectorAttr>(indices)) {
+    auto vecAttr = mlir::cast<cir::ConstVectorAttr>(vec);
+    auto indicesAttr = mlir::cast<cir::ConstVectorAttr>(indices);
+    auto vecTy = cast<cir::VectorType>(vecAttr.getType());
+
+    mlir::ArrayAttr vecElts = vecAttr.getElts();
+    mlir::ArrayAttr indicesElts = indicesAttr.getElts();
+
+    const uint64_t numElements = vecElts.size();
+
+    SmallVector<mlir::Attribute, 16> elements;
+    elements.reserve(numElements);
+
+    const uint64_t maskBits = llvm::NextPowerOf2(numElements - 1) - 1;
+    for (uint64_t i = 0; i < numElements; i++) {
+      cir::IntAttr idxAttr = mlir::cast<cir::IntAttr>(indicesElts[i]);
+      uint64_t idxValue = idxAttr.getUInt();
+      uint64_t newIdx = idxValue & maskBits;
+      elements.push_back(vecElts[newIdx]);
+    }
+
+    return cir::ConstVectorAttr::get(
+        vecTy, mlir::ArrayAttr::get(getContext(), elements));
+  }
+
+  return {};
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AmrDeveloper wrote:

As far as I understood, no, it should be null because that means we can't fold `VecShuffleDynamicOp` with non Const vec operands

https://github.com/llvm/llvm-project/pull/142315