Emit memmove, not memcpy, for structure copies; this is unfortunately

required for correctness in cases of copying a struct to itself or to 
an overlapping struct (itself for cases like *a = *a, and overlapping 
is possible with unions).

Hopefully, this won't end up being a perf issue; LLVM *should* be able 
to optimize memmove to memcpy in a lot of cases, and for small copies 
the generated code *should* be mostly comparable. (In reality, LLVM 
is currently horrible at optimizing memmove, but that's a bug, not a 
fundamental issue.)

gcc currently generates wrong code; that's 
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32667.

llvm-svn: 51566

1 files changed, 2 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index bc216e4f485..992a3bf3c22 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -59,6 +59,7 @@ class CodeGenModule {
   CGDebugInfo *DebugInfo;
 
   llvm::Function *MemCpyFn;
+  llvm::Function *MemMoveFn;
   llvm::Function *MemSetFn;
   llvm::DenseMap<const Decl*, llvm::Constant*> GlobalDeclMap;
   std::vector<const NamedDecl*> StaticDecls;
@@ -101,6 +102,7 @@ public:
   /// array containing the literal.  The result is pointer to array type.
   llvm::Constant *GetAddrOfConstantString(const std::string& str);
   llvm::Function *getMemCpyFn();
+  llvm::Function *getMemMoveFn();
   llvm::Function *getMemSetFn();
   llvm::Function *getIntrinsic(unsigned IID, const llvm::Type **Tys = 0, 
                                unsigned NumTys = 0);