When performing a trivial copy of a C++ type, we must be careful not

to overwrite objects that might have been allocated into the type's
tail padding.  This patch is missing some potential optimizations where
the destination is provably a complete object, but it's necessary for
correctness.

Patch by Jonathan Sauer.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162254 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 108 insertions, 16 deletions

diff --git a/include/clang/AST/ASTContext.h b/include/clang/AST/ASTContext.h
index cad3ad2b5f..47827e93f5 100644
--- a/include/clang/AST/ASTContext.h
+++ b/include/clang/AST/ASTContext.h
@@ -1427,6 +1427,10 @@ public:
   /// characters. This method does not work on incomplete types.
   CharUnits getTypeAlignInChars(QualType T) const;
   CharUnits getTypeAlignInChars(const Type *T) const;
+  
+  // getTypeInfoDataSizeInChars - Return the size of a type, in chars. If the
+  // type is a record, its data size is returned.
+  std::pair<CharUnits, CharUnits> getTypeInfoDataSizeInChars(QualType T) const;
 
   std::pair<CharUnits, CharUnits> getTypeInfoInChars(const Type *T) const;
   std::pair<CharUnits, CharUnits> getTypeInfoInChars(QualType T) const;
diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index 0452730201..7c685cf59a 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -1080,6 +1080,27 @@ CharUnits ASTContext::getDeclAlign(const Decl *D, bool RefAsPointee) const {
   return toCharUnitsFromBits(Align);
 }
 
+// getTypeInfoDataSizeInChars - Return the size of a type, in
+// chars. If the type is a record, its data size is returned.  This is
+// the size of the memcpy that's performed when assigning this type
+// using a trivial copy/move assignment operator.
+std::pair<CharUnits, CharUnits>
+ASTContext::getTypeInfoDataSizeInChars(QualType T) const {
+  std::pair<CharUnits, CharUnits> sizeAndAlign = getTypeInfoInChars(T);
+
+  // In C++, objects can sometimes be allocated into the tail padding
+  // of a base-class subobject.  We decide whether that's possible
+  // during class layout, so here we can just trust the layout results.
+  if (getLangOpts().CPlusPlus) {
+    if (const RecordType *RT = T->getAs<RecordType>()) {
+      const ASTRecordLayout &layout = getASTRecordLayout(RT->getDecl());
+      sizeAndAlign.first = layout.getDataSize();
+    }
+  }
+
+  return sizeAndAlign;
+}
+
 std::pair<CharUnits, CharUnits>
 ASTContext::getTypeInfoInChars(const Type *T) const {
   std::pair<uint64_t, unsigned> Info = getTypeInfo(T);
diff --git a/lib/CodeGen/CGExprAgg.cpp b/lib/CodeGen/CGExprAgg.cpp
index 61f7362eca..287b6dd8c7 100644
--- a/lib/CodeGen/CGExprAgg.cpp
+++ b/lib/CodeGen/CGExprAgg.cpp
@@ -1300,9 +1300,9 @@ void CodeGenFunction::EmitAggregateCopy(llvm::Value *DestPtr,
   // implementation handles this case safely.  If there is a libc that does not
   // safely handle this, we can add a target hook.
 
-  // Get size and alignment info for this aggregate.
+  // Get data size and alignment info for this aggregate.
   std::pair<CharUnits, CharUnits> TypeInfo = 
-    getContext().getTypeInfoInChars(Ty);
+    getContext().getTypeInfoDataSizeInChars(Ty);
 
   if (alignment.isZero())
     alignment = TypeInfo.second;
diff --git a/test/CodeGenObjCXX/implicit-copy-assign-operator.mm b/test/CodeGenObjCXX/implicit-copy-assign-operator.mm
index 29ec9acd38..a5ce789609 100644
--- a/test/CodeGenObjCXX/implicit-copy-assign-operator.mm
+++ b/test/CodeGenObjCXX/implicit-copy-assign-operator.mm
@@ -1,4 +1,6 @@
-// RUN: %clang_cc1 -fobjc-gc -emit-llvm -triple x86_64-apple-darwin10.0.0 -fobjc-runtime=macosx-fragile-10.5 -o - %s | FileCheck %s
+// RUN: %clang_cc1 -fobjc-gc -emit-llvm -triple x86_64-apple-darwin10.0.0 -fobjc-runtime=macosx-fragile-10.5 -o - %s | FileCheck %s -check-prefix=CHECK-OBJ
+// RUN: %clang_cc1 -x c++    -emit-llvm -triple x86_64-apple-darwin10.0.0                                    -o - %s | FileCheck %s -check-prefix=CHECK-CPP
+#ifdef __OBJC__
 struct A { 
   A &operator=(const A&);
   A &operator=(A&);
@@ -41,17 +43,82 @@ void test_D(D d1, D d2) {
   d1 = d2;
 }
 
-// CHECK: define linkonce_odr %struct.D* @_ZN1DaSERS_
-// CHECK: {{call.*_ZN1AaSERS_}}
-// CHECK: {{call.*_ZN1BaSERS_}}
-// CHECK: {{call.*_ZN1CaSERKS_}}
-// CHECK: {{call void @llvm.memcpy.p0i8.p0i8.i64.*i64 24}}
-// CHECK: {{call.*_ZN1BaSERS_}}
-// CHECK: br
-// CHECK: {{call.*_ZN1CaSERKS_}}
-// CHECK: {{call.*@objc_memmove_collectable}}
-// CHECK: {{call void @llvm.memcpy.p0i8.p0i8.i64.*i64 12}}
-// CHECK: call void @_ZN11CopyByValueC1ERKS_
-// CHECK: {{call.*_ZN11CopyByValueaSES_}}
-// CHECK: ret
+// CHECK-OBJ: define linkonce_odr %struct.D* @_ZN1DaSERS_
+// CHECK-OBJ: {{call.*_ZN1AaSERS_}}
+// CHECK-OBJ: {{call.*_ZN1BaSERS_}}
+// CHECK-OBJ: {{call.*_ZN1CaSERKS_}}
+// CHECK-OBJ: {{call void @llvm.memcpy.p0i8.p0i8.i64.*i64 24}}
+// CHECK-OBJ: {{call.*_ZN1BaSERS_}}
+// CHECK-OBJ: br
+// CHECK-OBJ: {{call.*_ZN1CaSERKS_}}
+// CHECK-OBJ: {{call.*@objc_memmove_collectable}}
+// CHECK-OBJ: {{call void @llvm.memcpy.p0i8.p0i8.i64.*i64 12}}
+// CHECK-OBJ: call void @_ZN11CopyByValueC1ERKS_
+// CHECK-OBJ: {{call.*_ZN11CopyByValueaSES_}}
+// CHECK-OBJ: ret
+#endif
 
+namespace PR13329 {
+#ifndef __OBJC__
+  typedef void* id;
+#endif
+  struct POD {
+    id    i;
+    short s;
+  };
+  
+  struct NonPOD {
+    id    i;
+    short s;
+    
+    NonPOD();
+  };
+  
+  struct DerivedNonPOD: NonPOD {
+    char  c;
+  };
+  
+  struct DerivedPOD: POD {
+    char  c;
+  };
+  
+  void testPOD() {
+    POD a;
+    POD b;
+    // CHECK-OBJ: @objc_memmove_collectable{{.*}}i64 16
+    // CHECK-CPP: @llvm.memcpy{{.*}}i64 16
+    b = a;
+  }
+  
+  void testNonPOD() {
+    NonPOD a;
+    NonPOD b;
+    // CHECK-OBJ: @objc_memmove_collectable{{.*}}i64 10
+    // CHECK-CPP: @llvm.memcpy{{.*}}i64 10
+    b = a;
+  }
+  
+  void testDerivedNonPOD() {
+    DerivedNonPOD a;
+    NonPOD        b;
+    DerivedNonPOD c;
+    // CHECK-OBJ: @objc_memmove_collectable{{.*}}i64 10
+    // CHECK-CPP: @llvm.memcpy{{.*}}i64 10
+    (NonPOD&) a = b;
+    // CHECK-OBJ: @objc_memmove_collectable{{.*}}i64 11
+    // CHECK-CPP: @llvm.memcpy{{.*}}i64 11
+    a = c;
+  };
+  
+  void testDerivedPOD() {
+    DerivedPOD a;
+    POD        b;
+    DerivedPOD c;
+    // CHECK-OBJ: @objc_memmove_collectable{{.*}}i64 16
+    // CHECK-CPP: @llvm.memcpy{{.*}}i64 16
+    (POD&) a = b;
+    // CHECK-OBJ: @objc_memmove_collectable{{.*}}i64 17
+    // CHECK-CPP: @llvm.memcpy{{.*}}i64 17
+    a = c;
+  };
+}