From: John McCall <rjmccall@apple.com>
Date: Tue, 13 Sep 2011 07:33:34 +0000 (+0000)
Subject: Don't use native atomics on ivars whose size is not a power of two,
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=c5d9a90b3a3c16324e0cceeccec3d2993888deb6;p=clang

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).



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@139590 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/clang/AST/CharUnits.h b/include/clang/AST/CharUnits.h
index d7cbd08e6c..5be35826a9 100644
--- a/include/clang/AST/CharUnits.h
+++ b/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/lib/CodeGen/CGObjC.cpp b/lib/CodeGen/CGObjC.cpp
index ca04a7b178..ddf6e1f98a 100644
--- a/lib/CodeGen/CGObjC.cpp
+++ b/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/test/CodeGenObjC/property-aggregate.m b/test/CodeGenObjC/property-aggregate.m
new file mode 100644
index 0000000000..f4b4dc9615
--- /dev/null
+++ b/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