[clang] [CIR] Upstream initial support for union type (PR #137501)

[Andy Kaylor via cfe-commits]

================
@@ -5,25 +5,146 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
 // RUN: FileCheck --check-prefix=OGCG --input-file=%t.ll %s
 
+union U1 {
+  int n;
+  char c;
+};
+
+// CIR:  !rec_U1 = !cir.record<union "U1" {!s32i, !s8i}>
+// LLVM: %union.U1 = type { i32 }
+// OGCG: %union.U1 = type { i32 }
+
+union U2 {
+  char b;
+  short s;
+  int i;
+  float f;
+  double d;
+};
+
+// CIR:  !rec_U2 = !cir.record<union "U2" {!s8i, !s16i, !s32i, !cir.float, !cir.double}>
+// LLVM: %union.U2 = type { double }
+// OGCG: %union.U2 = type { double }
+
 union IncompleteU *p;
 
-// CIR: cir.global external @p = #cir.ptr<null> : !cir.ptr<!rec_IncompleteU>
+// CIR:  cir.global external @p = #cir.ptr<null> : !cir.ptr<!rec_IncompleteU>
 // LLVM: @p = dso_local global ptr null
 // OGCG: @p = global ptr null, align 8
 
-void f(void) {
+void f1(void) {
   union IncompleteU *p;
 }
 
-// CIR: cir.func @f()
-// CIR-NEXT: cir.alloca !cir.ptr<!rec_IncompleteU>, !cir.ptr<!cir.ptr<!rec_IncompleteU>>, ["p"]
-// CIR-NEXT: cir.return
+// CIR:      cir.func @f1()
+// CIR-NEXT:   cir.alloca !cir.ptr<!rec_IncompleteU>, !cir.ptr<!cir.ptr<!rec_IncompleteU>>, ["p"]
+// CIR-NEXT:   cir.return
 
-// LLVM:      define void @f()
+// LLVM:      define void @f1()
 // LLVM-NEXT:   %[[P:.*]] = alloca ptr, i64 1, align 8
 // LLVM-NEXT:   ret void
 
-// OGCG:      define{{.*}} void @f()
+// OGCG:      define{{.*}} void @f1()
 // OGCG-NEXT: entry:
 // OGCG-NEXT:   %[[P:.*]] = alloca ptr, align 8
 // OGCG-NEXT:   ret void
+
+int f2(void) {
+  union U1 u;
+  u.n = 42;
+  return u.n;
+}
+
+// CIR:      cir.func @f2() -> !s32i
+// CIR-NEXT:   %0 = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"] {alignment = 4 : i64}
----------------
andykaylor wrote:

Use pattern matching to avoid hard-coding the %0, %1, etc. names throughout these tests, or just drop them from the check if they aren't referenced by a later check.

https://github.com/llvm/llvm-project/pull/137501