[clang] [CIR] Implement folder for VecShuffleOp (PR #143260)

[Bruno Cardoso Lopes via cfe-commits]

================
@@ -1580,9 +1580,46 @@ OpFoldResult cir::VecExtractOp::fold(FoldAdaptor adaptor) {
 }
 
 //===----------------------------------------------------------------------===//
-// VecShuffle
+// VecShuffleOp
 //===----------------------------------------------------------------------===//
 
+OpFoldResult cir::VecShuffleOp::fold(FoldAdaptor adaptor) {
+  auto vec1Attr =
+      mlir::dyn_cast_if_present<cir::ConstVectorAttr>(adaptor.getVec1());
+  auto vec2Attr =
+      mlir::dyn_cast_if_present<cir::ConstVectorAttr>(adaptor.getVec2());
+  if (!vec1Attr || !vec2Attr)
+    return {};
+
+  mlir::Type vec1ElemTy =
+      mlir::cast<cir::VectorType>(vec1Attr.getType()).getElementType();
+
+  mlir::ArrayAttr vec1Elts = vec1Attr.getElts();
+  mlir::ArrayAttr vec2Elts = vec2Attr.getElts();
+  mlir::ArrayAttr indicesElts = adaptor.getIndices();
+
+  SmallVector<mlir::Attribute, 16> elements;
+  elements.reserve(indicesElts.size());
+
+  uint64_t vec1Size = vec1Elts.size();
+  for (const auto &idxAttr : indicesElts.getAsRange<cir::IntAttr>()) {
+    if (idxAttr.getSInt() == -1) {
+      elements.push_back(cir::UndefAttr::get(vec1ElemTy));
+      continue;
+    }
+
+    uint64_t idxValue = idxAttr.getUInt();
+    if (idxValue < vec1Size) {
+      elements.push_back(vec1Elts[idxValue]);
+    } else {
+      elements.push_back(vec2Elts[idxValue - vec1Size]);
----------------
bcardosolopes wrote:

`elements.push_back(idxValue < vec1Size ? vec1Elts[idxValue] : vec2Elts[idxValue - vec1Size])`

https://github.com/llvm/llvm-project/pull/143260