[clang] [CIR][X86] Add support for kunpck builtins (PR #168757)

[Andy Kaylor via cfe-commits]

================
@@ -33,6 +33,28 @@ static mlir::Value emitIntrinsicCallOp(CIRGenFunction &cgf, const CallExpr *e,
       .getResult();
 }
 
+static mlir::Value getMaskVecValue(CIRGenBuilderTy &builder, mlir::Value mask,
+                                   unsigned numElems) {
+  auto maskIntType = mlir::cast<cir::IntType>(mask.getType());
+  unsigned maskWidth = maskIntType.getWidth();
+
+  // Create a vector of bool type with maskWidth elements
+  auto maskVecType =
+      cir::VectorType::get(builder.getContext(),
+                           cir::BoolType::get(builder.getContext()), maskWidth);
+  mlir::Value maskVec = builder.createBitcast(mask, maskVecType);
+
+  // If we have less than 8 elements, then the starting mask was an i8 and
+  // we need to extract down to the right number of elements.
+  if (numElems < 8) {
+    llvm::SmallVector<int64_t, 4> indices;
+    for (unsigned i = 0; i != numElems; ++i)
+      indices.push_back(i);
----------------
andykaylor wrote:

```suggestion
    SmallVector<mlir::Attribute, 4> indices;
    mlir::Type i32Ty = getSInt32Ty();
    for (auto i : llvm::seq<unsigned>(0, numElems))
      indices.push_back(cir::IntAttr::get(i32Ty, i);
```
If we don't do this here, `createVecShuffle` will loop through the vector again to do this.

https://github.com/llvm/llvm-project/pull/168757