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, 13 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index ec61d667eed..329599c1166 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -35,7 +35,8 @@ CodeGenModule::CodeGenModule(ASTContext &C, const LangOptions &LO,
                              llvm::Module &M, const llvm::TargetData &TD,
                              Diagnostic &diags, bool GenerateDebugInfo)
   : Context(C), Features(LO), TheModule(M), TheTargetData(TD), Diags(diags),
-    Types(C, M, TD), MemCpyFn(0), MemSetFn(0), CFConstantStringClassRef(0) {
+    Types(C, M, TD), MemCpyFn(0), MemMoveFn(0), MemSetFn(0),
+    CFConstantStringClassRef(0) {
   //TODO: Make this selectable at runtime
   Runtime = CreateObjCRuntime(M,
       getTypes().ConvertType(getContext().IntTy),
@@ -589,6 +590,17 @@ llvm::Function *CodeGenModule::getMemCpyFn() {
   return MemCpyFn = getIntrinsic(IID);
 }
 
+llvm::Function *CodeGenModule::getMemMoveFn() {
+  if (MemMoveFn) return MemMoveFn;
+  llvm::Intrinsic::ID IID;
+  switch (Context.Target.getPointerWidth(0)) {
+  default: assert(0 && "Unknown ptr width");
+  case 32: IID = llvm::Intrinsic::memmove_i32; break;
+  case 64: IID = llvm::Intrinsic::memmove_i64; break;
+  }
+  return MemMoveFn = getIntrinsic(IID);
+}
+
 llvm::Function *CodeGenModule::getMemSetFn() {
   if (MemSetFn) return MemSetFn;
   llvm::Intrinsic::ID IID;