Add test codegen test for attribute handling

Author: AaronBallman

clang/test/C/C23/n3037_1.c

@@ -1,5 +1,5 @@
 // NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 5
-// RUN: %clang_cc1 -std=c23 -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -std=c23 -Wno-error=odr -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s
 
 // This tests the codegen behavior of redefined tag types to ensure the
 // generated code looks reasonable.
@@ -46,3 +46,43 @@ enum E {
   One,
   Two
 };
+
+// Ensure that ignoring the incompatibility due to attributes does not cause a
+// crash. Note, this is undefined behavior in Clang until we implement
+// attribute structural compatibility logic, so this is not intended to verify
+// any particular behavior beyond "don't crash."
+struct T {
+  _Alignas(double) int x;
+};
+
+// CHECK-LABEL: define dso_local i32 @foo(
+// CHECK-SAME: i32 [[T_COERCE:%.*]]) #[[ATTR0]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[T:%.*]] = alloca [[STRUCT_T:%.*]], align 8
+// CHECK-NEXT:    [[COERCE_DIVE:%.*]] = getelementptr inbounds nuw [[STRUCT_T]], ptr [[T]], i32 0, i32 0
+// CHECK-NEXT:    store i32 [[T_COERCE]], ptr [[COERCE_DIVE]], align 8
+// CHECK-NEXT:    [[X:%.*]] = getelementptr inbounds nuw [[STRUCT_T]], ptr [[T]], i32 0, i32 0
+// CHECK-NEXT:    [[TMP0:%.*]] = load i32, ptr [[X]], align 8
+// CHECK-NEXT:    ret i32 [[TMP0]]
+//
+int foo(struct T t) {
+  return t.x;
+}
+
+struct T {
+  int x;
+};
+
+// CHECK-LABEL: define dso_local i32 @bar(
+// CHECK-SAME: i32 [[T_COERCE:%.*]]) #[[ATTR0]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[T:%.*]] = alloca [[STRUCT_T:%.*]], align 8
+// CHECK-NEXT:    [[COERCE_DIVE:%.*]] = getelementptr inbounds nuw [[STRUCT_T]], ptr [[T]], i32 0, i32 0
+// CHECK-NEXT:    store i32 [[T_COERCE]], ptr [[COERCE_DIVE]], align 8
+// CHECK-NEXT:    [[X:%.*]] = getelementptr inbounds nuw [[STRUCT_T]], ptr [[T]], i32 0, i32 0
+// CHECK-NEXT:    [[TMP0:%.*]] = load i32, ptr [[X]], align 8
+// CHECK-NEXT:    ret i32 [[TMP0]]
+//
+int bar(struct T t) {
+  return t.x;
+}