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-rw-r--r--lib/CodeGen/CGCall.cpp25
1 files changed, 25 insertions, 0 deletions
diff --git a/lib/CodeGen/CGCall.cpp b/lib/CodeGen/CGCall.cpp
index 9e97bce6c3..9318973e64 100644
--- a/lib/CodeGen/CGCall.cpp
+++ b/lib/CodeGen/CGCall.cpp
@@ -1614,6 +1614,18 @@ static llvm::StoreInst *findDominatingStoreToReturnValue(CodeGenFunction &CGF) {
return store;
}
+/// Check whether 'this' argument of a callsite matches 'this' of the caller.
+static bool checkThisPointer(llvm::Value *ThisArg, llvm::Value *This) {
+ if (ThisArg == This)
+ return true;
+ // Check whether ThisArg is a bitcast of This.
+ llvm::BitCastInst *Bitcast;
+ if ((Bitcast = dyn_cast<llvm::BitCastInst>(ThisArg)) &&
+ Bitcast->getOperand(0) == This)
+ return true;
+ return false;
+}
+
void CodeGenFunction::EmitFunctionEpilog(const CGFunctionInfo &FI) {
// Functions with no result always return void.
if (ReturnValue == 0) {
@@ -1705,6 +1717,19 @@ void CodeGenFunction::EmitFunctionEpilog(const CGFunctionInfo &FI) {
llvm_unreachable("Invalid ABI kind for return argument");
}
+ // If this function returns 'this', the last instruction is a CallInst
+ // that returns 'this', and 'this' argument of the CallInst points to
+ // the same object as CXXThisValue, use the return value from the CallInst.
+ // We will not need to keep 'this' alive through the callsite. It also enables
+ // optimizations in the backend, such as tail call optimization.
+ if (CalleeWithThisReturn && CGM.getCXXABI().HasThisReturn(CurGD)) {
+ llvm::BasicBlock *IP = Builder.GetInsertBlock();
+ llvm::CallInst *Callsite;
+ if (!IP->empty() && (Callsite = dyn_cast<llvm::CallInst>(&IP->back())) &&
+ Callsite->getCalledFunction() == CalleeWithThisReturn &&
+ checkThisPointer(Callsite->getOperand(0), CXXThisValue))
+ RV = Builder.CreateBitCast(Callsite, RetAI.getCoerceToType());
+ }
llvm::Instruction *Ret = RV ? Builder.CreateRet(RV) : Builder.CreateRetVoid();
if (!RetDbgLoc.isUnknown())
Ret->setDebugLoc(RetDbgLoc);