Don't use native atomics on ivars whose size is not a power of two,

even on architectures that support unaligned access (which is the
only way this is otherwise legal, given that ivars apparently do
not honor alignment attributes).

llvm-svn: 139590

3 files changed, 43 insertions, 0 deletions

diff --git a/clang/include/clang/AST/CharUnits.h b/clang/include/clang/AST/CharUnits.h
index d7cbd08e6c2..5be35826a96 100644
--- a/clang/include/clang/AST/CharUnits.h
+++ b/clang/include/clang/AST/CharUnits.h
@@ -125,6 +125,12 @@ namespace clang {
       /// isNegative - Test whether the quantity is less than zero.
       bool isNegative() const { return Quantity  < 0; }
 
+      /// isPowerOfTwo - Test whether the quantity is a power of two.
+      /// Zero is not a power of two.
+      bool isPowerOfTwo() const {
+        return (Quantity & -Quantity) == Quantity;
+      }
+
       // Arithmetic operators.
       CharUnits operator* (QuantityType N) const {
         return CharUnits(Quantity * N);
diff --git a/clang/lib/CodeGen/CGObjC.cpp b/clang/lib/CodeGen/CGObjC.cpp
index ca04a7b1785..ddf6e1f98a7 100644
--- a/clang/lib/CodeGen/CGObjC.cpp
+++ b/clang/lib/CodeGen/CGObjC.cpp
@@ -527,6 +527,14 @@ PropertyImplStrategy::PropertyImplStrategy(CodeGenModule &CGM,
 
   // Otherwise, this is target-dependent and based on the size and
   // alignment of the ivar.
+
+  // If the size of the ivar is not a power of two, give up.  We don't
+  // want to get into the business of doing compare-and-swaps.
+  if (!IvarSize.isPowerOfTwo()) {
+    Kind = CopyStruct;
+    return;
+  }
+
   llvm::Triple::ArchType arch =
     CGM.getContext().getTargetInfo().getTriple().getArch();
 
diff --git a/clang/test/CodeGenObjC/property-aggregate.m b/clang/test/CodeGenObjC/property-aggregate.m
new file mode 100644
index 00000000000..f4b4dc96151
--- /dev/null
+++ b/clang/test/CodeGenObjC/property-aggregate.m
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -fobjc-nonfragile-abi -emit-llvm %s -o - | FileCheck %s
+
+// This structure's size is not a power of two, so the property does
+// not get native atomics, even though x86-64 can do unaligned atomics
+// with a lock prefix.
+struct s3 { char c[3]; };
+
+// This structure's size is, so it does, because it can.
+struct s4 { char c[4]; };
+
+@interface Test0
+@property struct s3 s3;
+@property struct s4 s4;
+@end
+@implementation Test0
+@synthesize s3, s4;
+@end
+
+// CHECK: define internal i24 @"\01-[Test0 s3]"(
+// CHECK: call void @objc_copyStruct
+
+// CHECK: define internal void @"\01-[Test0 setS3:]"(
+// CHECK: call void @objc_copyStruct
+
+// CHECK: define internal i32 @"\01-[Test0 s4]"(
+// CHECK: load atomic i32* {{%.*}} unordered, align 1
+
+// CHECK: define internal void @"\01-[Test0 setS4:]"(
+// CHECK: store atomic i32 {{%.*}}, i32* {{%.*}} unordered, align 1