[CodeGen][AArch64] Fix AArch64ABIInfo::EmitAAPCSVAArg crash with empty record type in variadic arg

Fix AArch64ABIInfo::EmitAAPCSVAArg crash with empty record type in variadic arg

Open issue: #59034

Reviewed By: rjmccall

Differential Revision: https://reviews.llvm.org/D138511

Author: yronglin

clang/lib/CodeGen/TargetInfo.cpp

@@ -5998,6 +5998,16 @@ Address AArch64ABIInfo::EmitAAPCSVAArg(Address VAListAddr, QualType Ty,
                                        CodeGenFunction &CGF) const {
   ABIArgInfo AI = classifyArgumentType(Ty, /*IsVariadic=*/true,
                                        CGF.CurFnInfo->getCallingConvention());
+  // Empty records are ignored for parameter passing purposes.
+  if (AI.isIgnore()) {
+    uint64_t PointerSize = getTarget().getPointerWidth(LangAS::Default) / 8;
+    CharUnits SlotSize = CharUnits::fromQuantity(PointerSize);
+    VAListAddr = CGF.Builder.CreateElementBitCast(VAListAddr, CGF.Int8PtrTy);
+    auto *Load = CGF.Builder.CreateLoad(VAListAddr);
+    Address Addr = Address(Load, CGF.Int8Ty, SlotSize);
+    return CGF.Builder.CreateElementBitCast(Addr, CGF.ConvertTypeForMem(Ty));
+  }
+
   bool IsIndirect = AI.isIndirect();
 
   llvm::Type *BaseTy = CGF.ConvertType(Ty);

clang/test/CodeGen/aarch64-varargs.c

@@ -894,4 +894,10 @@ void check_start(int n, ...) {
 // CHECK: call void @llvm.va_start(i8* [[VOIDP_THE_LIST]])
 }
 
-
+typedef struct {} empty;
+empty empty_record_test(void) {
+// CHECK-LABEL: define{{.*}} void @empty_record_test()
+  return va_arg(the_list, empty);
+// CHECK: [[GR_OFFS:%[a-z_0-9]+]] = load i8*, i8** getelementptr inbounds (%struct.__va_list, %struct.__va_list* @the_list, i32 0, i32 0)
+// CHECK: [[ADDR:%[a-z._0-9]+]] = bitcast i8* [[GR_OFFS]] to %struct.empty*
+}