[clang] [CIR] Upstream local initialization for VectorType (PR #138107)

[Andy Kaylor via cfe-commits]

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@@ -1685,6 +1686,29 @@ mlir::LogicalResult CIRToLLVMStackRestoreOpLowering::matchAndRewrite(
   return mlir::success();
 }
 
+mlir::LogicalResult CIRToLLVMVecCreateOpLowering::matchAndRewrite(
+    cir::VecCreateOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  // Start with an 'undef' value for the vector.  Then 'insertelement' for
+  // each of the vector elements.
+  const auto vecTy = mlir::cast<cir::VectorType>(op.getType());
+  const mlir::Type llvmTy = typeConverter->convertType(vecTy);
+  const mlir::Location loc = op.getLoc();
+  mlir::Value result = rewriter.create<mlir::LLVM::PoisonOp>(loc, llvmTy);
+  assert(vecTy.getSize() == op.getElements().size() &&
+         "cir.vec.create op count doesn't match vector type elements count");
+
+  for (uint64_t i = 0; i < vecTy.getSize(); ++i) {
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andykaylor wrote:

OK. We can possibly revisit this later. For constant values, it looks like it ends up as a single store in LLVM IR anyway.

https://github.com/llvm/llvm-project/pull/138107