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

[Henrich Lauko 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]);
----------------
xlauko wrote:

This might use `getAsValueRange()` on `indicesElts` to remove cast and use range for?

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