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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@51566 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/CGExprAgg.cpp b/lib/CodeGen/CGExprAgg.cpp
index f584980d7f8af1a12ae5ecdf676261a2bd789bb6..30ff9ecbaf35a0422f8bd32a4f664b48810fbadd 100644 (file)
--- a/lib/CodeGen/CGExprAgg.cpp
+++ b/lib/CodeGen/CGExprAgg.cpp
@@ -131,7 +131,7 @@ void AggExprEmitter::EmitAggregateCopy(llvm::Value *DestPtr,
                                        llvm::Value *SrcPtr, QualType Ty) {
   assert(!Ty->isAnyComplexType() && "Shouldn't happen for complex");
   
-  // Aggregate assignment turns into llvm.memcpy.
+  // Aggregate assignment turns into llvm.memmove.
   const llvm::Type *BP = llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
   if (DestPtr->getType() != BP)
     DestPtr = Builder.CreateBitCast(DestPtr, BP, "tmp");
@@ -144,14 +144,14 @@ void AggExprEmitter::EmitAggregateCopy(llvm::Value *DestPtr,
   // FIXME: Handle variable sized types.
   const llvm::Type *IntPtr = llvm::IntegerType::get(CGF.LLVMPointerWidth);
   
-  llvm::Value *MemCpyOps[4] = {
+  llvm::Value *MemMoveOps[4] = {
     DestPtr, SrcPtr,
     // TypeInfo.first describes size in bits.
     llvm::ConstantInt::get(IntPtr, TypeInfo.first/8),
     llvm::ConstantInt::get(llvm::Type::Int32Ty, TypeInfo.second/8)
   };
   
-  Builder.CreateCall(CGF.CGM.getMemCpyFn(), MemCpyOps, MemCpyOps+4);
+  Builder.CreateCall(CGF.CGM.getMemMoveFn(), MemMoveOps, MemMoveOps+4);
 }
 
 

diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index ec61d667eed035adc36dc8c73028e7ad326bb728..329599c1166b8b3327d2242ecdad2ba79168bbfe 100644 (file)
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/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;

diff --git a/lib/CodeGen/CodeGenModule.h b/lib/CodeGen/CodeGenModule.h
index bc216e4f4852728a0bb5ae76a9a5dfc386d96f6e..992a3bf3c226eceb73842b83fc8af3c950e17cef 100644 (file)
--- a/lib/CodeGen/CodeGenModule.h
+++ b/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);