Rework the Sema/AST/IRgen dance for the lambda closure type's

conversion to function pointer. Rather than having IRgen synthesize
the body of this function, we instead introduce a static member
function "__invoke" with the same signature as the lambda's
operator() in the AST. Sema then generates a body for the conversion
to function pointer which simply returns the address of __invoke. This
approach makes it easier to evaluate a call to the conversion function
as a constant, makes the linkage of the __invoke function follow the
normal rules for member functions, and may make life easier down the
road if we ever want to constexpr'ify some of lambdas.

Note that IR generation is responsible for filling in the body of
__invoke (Sema just adds a dummy body), because the body can't
generally be expressed in C++.

Eli, please review!


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150783 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 20 insertions, 62 deletions

diff --git a/lib/CodeGen/CGClass.cpp b/lib/CodeGen/CGClass.cpp
index ed44679a88..7e94af391f 100644
--- a/lib/CodeGen/CGClass.cpp
+++ b/lib/CodeGen/CGClass.cpp
@@ -1725,26 +1725,15 @@ void CodeGenFunction::EmitLambdaToBlockPointerBody(FunctionArgList &Args) {
   CGM.ErrorUnsupported(CurFuncDecl, "lambda conversion to block");
 }
 
-void CodeGenFunction::EmitLambdaThunkBody(llvm::Function *Fn,
-                                          const CGFunctionInfo &FnInfo,
-                                          const CXXRecordDecl *Lambda) {
+void CodeGenFunction::EmitLambdaDelegatingInvokeBody(const CXXMethodDecl *MD) {
+  const CXXRecordDecl *Lambda = MD->getParent();
   DeclarationName Name
     = getContext().DeclarationNames.getCXXOperatorName(OO_Call);
   DeclContext::lookup_const_result Calls = Lambda->lookup(Name);
-  CXXMethodDecl *MD = cast<CXXMethodDecl>(*Calls.first++);
+  CXXMethodDecl *CallOperator = cast<CXXMethodDecl>(*Calls.first++);
   const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
   QualType ResultType = FPT->getResultType();
 
-  // Begin function
-  FunctionArgList FunctionArgs;
-  for (FunctionDecl::param_const_iterator I = MD->param_begin(),
-       E = MD->param_end(); I != E; ++I) {
-    ParmVarDecl *Param = *I;
-    FunctionArgs.push_back(Param);
-  }
-  StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
-                SourceLocation());
-
   // Start building arguments for forwarding call
   CallArgList CallArgs;
 
@@ -1760,7 +1749,7 @@ void CodeGenFunction::EmitLambdaThunkBody(llvm::Function *Fn,
   }
 
   // Get the address of the call operator.
-  GlobalDecl GD(MD);
+  GlobalDecl GD(CallOperator);
   const CGFunctionInfo &CalleeFnInfo = CGM.getTypes().getFunctionInfo(GD);
   llvm::Type *Ty =
     CGM.getTypes().GetFunctionType(CalleeFnInfo, FPT->isVariadic());
@@ -1769,54 +1758,24 @@ void CodeGenFunction::EmitLambdaThunkBody(llvm::Function *Fn,
   // Determine whether we have a return value slot to use.
   ReturnValueSlot Slot;
   if (!ResultType->isVoidType() &&
-      FnInfo.getReturnInfo().getKind() == ABIArgInfo::Indirect &&
+      CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect &&
       hasAggregateLLVMType(CurFnInfo->getReturnType()))
     Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified());
   
   // Now emit our call.
-  RValue RV = EmitCall(CalleeFnInfo, Callee, Slot, CallArgs, MD);
+  RValue RV = EmitCall(CalleeFnInfo, Callee, Slot, CallArgs, CallOperator);
 
   // Forward the returned value
   if (!ResultType->isVoidType() && Slot.isNull())
     EmitReturnOfRValue(RV, ResultType);
-
-  // End the function.
-  FinishFunction();
 }
 
-llvm::Constant *
-CodeGenFunction::EmitLambdaConvertedFnPtr(const CXXMethodDecl *MD) {
-  QualType FnTy = MD->getResultType()->getPointeeType();
-  CanQual<FunctionProtoType> CanFnTy =
-      CGM.getContext().getCanonicalType(FnTy)->getAs<FunctionProtoType>();
-  llvm::FunctionType *FnLLVMTy = cast<llvm::FunctionType>(CGM.getTypes().ConvertType(FnTy));
-  const CXXRecordDecl *Lambda = MD->getParent();
-  const CGFunctionInfo &FnInfo = CGM.getTypes().getFunctionInfo(CanFnTy);
-
-  if (CanFnTy->isVariadic()) {
+void CodeGenFunction::EmitLambdaStaticInvokeFunction(const CXXMethodDecl *MD) {
+  if (MD->isVariadic()) {
     // FIXME: Making this work correctly is nasty because it requires either
     // cloning the body of the call operator or making the call operator forward.
     CGM.ErrorUnsupported(MD, "lambda conversion to variadic function");
-    return llvm::UndefValue::get(FnLLVMTy->getPointerTo());
   }
 
-  // Build a declaration for the function which this function will
-  // return a pointer to.
-  // FIXME: Should the "thunk" actually be part of the AST?  That would allow
-  // the conversion to function pointer to be constexpr...
-  std::string MangledName =
-      (llvm::Twine(CurFn->getName()) + "_lambdacallthunk").str();
-  llvm::Function *Fn =
-      llvm::Function::Create(FnLLVMTy, llvm::Function::InternalLinkage,
-                            MangledName, &CGM.getModule());
-
-  // Emit the definition of the new function.
-  CodeGenFunction(CGM).EmitLambdaThunkBody(Fn, FnInfo, Lambda);
-  return Fn;
-}
-
-void CodeGenFunction::EmitLambdaToFunctionPointerBody(FunctionArgList &Args) {
-  const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurFuncDecl);
-  EmitReturnOfRValue(RValue::get(EmitLambdaConvertedFnPtr(MD)),
-                     MD->getResultType());
+  EmitLambdaDelegatingInvokeBody(MD);
 }
diff --git a/lib/CodeGen/CodeGenFunction.cpp b/lib/CodeGen/CodeGenFunction.cpp
index 1034de736c..28c5935de0 100644
--- a/lib/CodeGen/CodeGenFunction.cpp
+++ b/lib/CodeGen/CodeGenFunction.cpp
@@ -448,13 +448,15 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
            FD->hasAttr<CUDAGlobalAttr>())
     CGM.getCUDARuntime().EmitDeviceStubBody(*this, Args);
   else if (isa<CXXConversionDecl>(FD) &&
-           cast<CXXConversionDecl>(FD)->getParent()->isLambda()) {
-    // The lambda conversion operators are special; the semantics can't be
-    // expressed in the AST, so IRGen needs to special-case them.
-    if (cast<CXXConversionDecl>(FD)->isLambdaToBlockPointerConversion())
-      EmitLambdaToBlockPointerBody(Args);
-    else
-      EmitLambdaToFunctionPointerBody(Args);
+           cast<CXXConversionDecl>(FD)->isLambdaToBlockPointerConversion()) {
+    // The lambda conversion to block pointer is special; the semantics can't be
+    // expressed in the AST, so IRGen needs to special-case it.
+    EmitLambdaToBlockPointerBody(Args);
+  } else if (isa<CXXMethodDecl>(FD) &&
+             cast<CXXMethodDecl>(FD)->isLambdaStaticInvoker()) {
+    // The lambda "__invoke" function is special, because it forwards or
+    // clones the body of the function call operator (but is actually static).
+    EmitLambdaStaticInvokeFunction(cast<CXXMethodDecl>(FD));
   }
   else
     EmitFunctionBody(Args);
diff --git a/lib/CodeGen/CodeGenFunction.h b/lib/CodeGen/CodeGenFunction.h
index 2b9b8ab7b8..427ee08e69 100644
--- a/lib/CodeGen/CodeGenFunction.h
+++ b/lib/CodeGen/CodeGenFunction.h
@@ -1377,11 +1377,8 @@ public:
   void EmitFunctionBody(FunctionArgList &Args);
 
   void EmitLambdaToBlockPointerBody(FunctionArgList &Args);
-  void EmitLambdaToFunctionPointerBody(FunctionArgList &Args);
-  llvm::Constant *EmitLambdaConvertedFnPtr(const CXXMethodDecl *MD);
-  void EmitLambdaThunkBody(llvm::Function *Fn,
-                           const CGFunctionInfo &FnInfo,
-                           const CXXRecordDecl *Lambda);
+  void EmitLambdaDelegatingInvokeBody(const CXXMethodDecl *MD);
+  void EmitLambdaStaticInvokeFunction(const CXXMethodDecl *MD);
 
   /// EmitReturnBlock - Emit the unified return block, trying to avoid its
   /// emission when possible.