[clang] [Clang] Add FileCheck lines to atomic-auto-type codegen test (PR #206749)

[Erich Keane via cfe-commits]

================
@@ -1,10 +1,40 @@
-// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -emit-llvm -o - %s > /dev/null
-
-// This is a regression test for handling of __auto_type inside _Atomic.
-// Previously this could lead to an undeduced AutoType escaping into
-// ASTContext::getTypeInfoImpl and causing an assertion failure.
-
-void f(double x) {
-  __auto_type _Atomic xa = x;
-  _Atomic __auto_type ax = x;
-}
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -std=c11 -emit-llvm -o - %s | FileCheck %s
+
+// This is a regression test for handling of __auto_type inside _Atomic.
+// Previously this could lead to an undeduced AutoType escaping into
+// ASTContext::getTypeInfoImpl and causing an assertion failure.
+
+// 24-byte struct exceeds the lock-free threshold on x86_64.
+struct Large { double a, b, c; };
+
+// _Atomic double is lock-free on x86_64: deduced type lowers to plain stores.
+// CHECK-LABEL: @test_atomic_auto_type(
+// CHECK:      alloca double
+// CHECK-NEXT: %[[XA:.*]] = alloca double
+// CHECK-NEXT: %[[AX:.*]] = alloca double
+// CHECK:      store double {{.*}}, ptr %[[XA]]
+// CHECK:      store double {{.*}}, ptr %[[AX]]
+// CHECK:      ret void
+
+void test_atomic_auto_type(double x) {
+  __auto_type _Atomic xa = x;
+  _Atomic __auto_type ax = x;
+}
+
+// _Atomic struct Large is not lock-free, so assignments (which must be atomic)
+// call __atomic_store. Initialization of _Atomic is not required to be atomic.
+// CHECK-LABEL: @test_atomic_auto_type_lock(
+// CHECK:      %[[LA:.*]] = alloca %struct.Large
+// CHECK-NEXT: %[[AL:.*]] = alloca %struct.Large
+// CHECK:      call void @llvm.memcpy{{.*}}%[[LA]]
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erichkeane wrote:

Add parens/commas to the memcpy and atomic_store checks, just so we know that it is the correct 'arity'.

Else this patch lgtm.

https://github.com/llvm/llvm-project/pull/206749