[clang] [CIR] Upstream proper function alias lowering (PR #150520)

[Henrich Lauko via cfe-commits]

================
@@ -1166,6 +1199,31 @@ void CIRToLLVMFuncOpLowering::lowerFuncAttributes(
   }
 }
 
+mlir::LogicalResult CIRToLLVMFuncOpLowering::matchAndRewriteAlias(
+    cir::FuncOp op, mlir::FlatSymbolRefAttr aliasee, mlir::Type ty,
+    OpAdaptor adaptor, mlir::ConversionPatternRewriter &rewriter) const {
+  SmallVector<mlir::NamedAttribute, 4> attributes;
+  lowerFuncAttributes(op, /*filterArgAndResAttrs=*/false, attributes);
+
+  mlir::Location loc = op.getLoc();
+  auto aliasOp = rewriter.replaceOpWithNewOp<mlir::LLVM::AliasOp>(
+      op, ty, convertLinkage(op.getLinkage()), op.getName(), op.getDsoLocal(),
+      /*threadLocal=*/false, attributes);
+
+  // Create the alias body
+  mlir::OpBuilder builder(op.getContext());
+  mlir::Block *block = builder.createBlock(&aliasOp.getInitializerRegion());
+  builder.setInsertionPointToStart(block);
+  // The type of AddressOfOp is always a pointer.
+  assert(!cir::MissingFeatures::addressSpace());
+  mlir::Type ptrTy = mlir::LLVM::LLVMPointerType::get(ty.getContext());
+  auto addrOp =
+      builder.create<mlir::LLVM::AddressOfOp>(loc, ptrTy, aliasee.getValue());
+  builder.create<mlir::LLVM::ReturnOp>(loc, addrOp);
----------------
xlauko wrote:

```suggestion
  auto addrOp =
      mlir::LLVM::AddressOfOp::create(builder, loc, ptrTy, aliasee.getValue());
  mlir::LLVM::ReturnOp::(builder, loc, addrOp);
```

https://github.com/llvm/llvm-project/pull/150520