[CIR][CIRGen] Generate CIR for empty compound literal (#880)

as title.

Author: ghehg

clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp

@@ -340,8 +340,8 @@ class ScalarExprEmitter : public StmtVisitor<ScalarExprEmitter, mlir::Value> {
   }
 
   mlir::Value VisitMemberExpr(MemberExpr *E);
-  mlir::Value VisitCompoundLiteralEpxr(CompoundLiteralExpr *E) {
-    llvm_unreachable("NYI");
+  mlir::Value VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
+    return buildLoadOfLValue(E);
   }
 
   mlir::Value VisitInitListExpr(InitListExpr *E);
@@ -1930,7 +1930,7 @@ mlir::Value ScalarExprEmitter::VisitInitListExpr(InitListExpr *E) {
 
   if (NumInitElements == 0) {
     // C++11 value-initialization for the scalar.
-    llvm_unreachable("NYI");
+    return buildNullValue(E->getType(), CGF.getLoc(E->getExprLoc()));
   }
 
   return Visit(E->getInit(0));

clang/test/CIR/CodeGen/compound-literal-empty.c

@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -triple aarch64-none-linux-android21 -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -triple aarch64-none-linux-android21 -fclangir -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=LLVM
+
+short b() { return (short){}; }
+
+// CIR-LABEL: b
+// CIR: {{%.*}} = cir.alloca !s16i, !cir.ptr<!s16i>, [".compoundliteral"] {alignment = 2 : i64}
+
+// LLVM-LABEL: b
+// LLVM: [[RET_P:%.*]] = alloca i16, i64 1, align 2
+// LLVM: [[LITERAL:%.*]] =  alloca i16, i64 1, align 2
+// LLVM: store i16 0, ptr [[LITERAL]], align 2
+// LLVM: [[T0:%.*]] = load i16, ptr [[LITERAL]], align 2
+// LLVM: store i16 [[T0]], ptr [[RET_P]], align 2
+// LLVM: [[T1:%.*]] = load i16, ptr [[RET_P]], align 2
+// LLVM: ret i16 [[T1]]