[PATCH] D46613: _Atomic of empty struct shouldn't assert

[JF Bastien via Phabricator via cfe-commits]

jfb updated this revision to Diff 145858.
jfb added a comment.

- Assert on zero alignment, instead of making it always byte-aligned.


Repository:
  rC Clang

https://reviews.llvm.org/D46613

Files:
  lib/AST/ASTContext.cpp
  test/CodeGen/c11atomics-ios.c
  test/CodeGen/c11atomics.c


Index: test/CodeGen/c11atomics.c
===================================================================
--- test/CodeGen/c11atomics.c
+++ test/CodeGen/c11atomics.c
@@ -474,3 +474,17 @@
   // CHECK:   ret i1 [[RES]]
   return __c11_atomic_compare_exchange_strong(addr, desired, *new, 5, 5);
 }
+
+struct Empty {};
+
+struct Empty test_empty_struct_load(_Atomic(struct Empty)* empty) {
+  // CHECK-LABEL: @test_empty_struct_load(
+  // CHECK: call arm_aapcscc zeroext i8 @__atomic_load_1(i8* %{{.*}}, i32 5)
+  return __c11_atomic_load(empty, 5);
+}
+
+void test_empty_struct_store(_Atomic(struct Empty)* empty, struct Empty value) {
+  // CHECK-LABEL: @test_empty_struct_store(
+  // CHECK: call arm_aapcscc void @__atomic_store_1(i8* %{{.*}}, i8 zeroext %{{.*}}, i32 5)
+  __c11_atomic_store(empty, value, 5);
+}
Index: test/CodeGen/c11atomics-ios.c
===================================================================
--- test/CodeGen/c11atomics-ios.c
+++ test/CodeGen/c11atomics-ios.c
@@ -319,3 +319,19 @@
 
   return __c11_atomic_compare_exchange_strong(addr, desired, *new, 5, 5);
 }
+
+struct Empty {};
+
+struct Empty testEmptyStructLoad(_Atomic(struct Empty)* empty) {
+  // CHECK-LABEL: @testEmptyStructLoad(
+  // CHECK-NOT: @__atomic_load
+  // CHECK: load atomic i8, i8* %{{.*}} seq_cst, align 1
+  return *empty;
+}
+
+void testEmptyStructStore(_Atomic(struct Empty)* empty, struct Empty value) {
+  // CHECK-LABEL: @testEmptyStructStore(
+  // CHECK-NOT: @__atomic_store
+  // CHECK: store atomic i8 %{{.*}}, i8* %{{.*}} seq_cst, align 1
+  *empty = value;
+}
Index: lib/AST/ASTContext.cpp
===================================================================
--- lib/AST/ASTContext.cpp
+++ lib/AST/ASTContext.cpp
@@ -1958,10 +1958,16 @@
     Width = Info.Width;
     Align = Info.Align;
 
-    // If the size of the type doesn't exceed the platform's max
-    // atomic promotion width, make the size and alignment more
-    // favorable to atomic operations:
-    if (Width != 0 && Width <= Target->getMaxAtomicPromoteWidth()) {
+    if (!Width) {
+      // An otherwise zero-sized type should still generate an
+      // atomic operation.
+      Width = Target->getCharWidth();
+      assert(Align);
+    } else if (Width <= Target->getMaxAtomicPromoteWidth()) {
+      // If the size of the type doesn't exceed the platform's max
+      // atomic promotion width, make the size and alignment more
+      // favorable to atomic operations:
+
       // Round the size up to a power of 2.
       if (!llvm::isPowerOf2_64(Width))
         Width = llvm::NextPowerOf2(Width);


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