CodeGen: Have 'this'-returning constructors and destructors to take advantage of the new backend 'returned' attribute.
The backend will now use the generic 'returned' attribute to form tail calls where possible, as well as avoid save-restores of 'this' in some cases (specifically the cases that matter for the ARM C++ ABI).
This patch also reverts a prior front-end only partial implementation of these optimizations, since it's no longer required.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184205 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/ItaniumCXXABI.cpp b/lib/CodeGen/ItaniumCXXABI.cpp
index 6cf95b5..7228400 100644
--- a/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/lib/CodeGen/ItaniumCXXABI.cpp
@@ -119,13 +119,14 @@
void EmitInstanceFunctionProlog(CodeGenFunction &CGF);
- llvm::Value *EmitConstructorCall(CodeGenFunction &CGF,
- const CXXConstructorDecl *D,
- CXXCtorType Type, bool ForVirtualBase,
- bool Delegating,
- llvm::Value *This,
- CallExpr::const_arg_iterator ArgBeg,
- CallExpr::const_arg_iterator ArgEnd);
+ RValue EmitConstructorCall(CodeGenFunction &CGF,
+ const CXXConstructorDecl *D,
+ CXXCtorType Type,
+ bool ForVirtualBase, bool Delegating,
+ ReturnValueSlot ReturnValue,
+ llvm::Value *This,
+ CallExpr::const_arg_iterator ArgBeg,
+ CallExpr::const_arg_iterator ArgEnd);
RValue EmitVirtualDestructorCall(CodeGenFunction &CGF,
const CXXDestructorDecl *Dtor,
@@ -165,21 +166,11 @@
public:
ARMCXXABI(CodeGen::CodeGenModule &CGM) : ItaniumCXXABI(CGM, /*ARM*/ true) {}
- void BuildConstructorSignature(const CXXConstructorDecl *Ctor,
- CXXCtorType T,
- CanQualType &ResTy,
- SmallVectorImpl<CanQualType> &ArgTys);
-
- void BuildDestructorSignature(const CXXDestructorDecl *Dtor,
- CXXDtorType T,
- CanQualType &ResTy,
- SmallVectorImpl<CanQualType> &ArgTys);
-
- void BuildInstanceFunctionParams(CodeGenFunction &CGF,
- QualType &ResTy,
- FunctionArgList &Params);
-
- void EmitInstanceFunctionProlog(CodeGenFunction &CGF);
+ bool HasThisReturn(GlobalDecl GD) const {
+ return (isa<CXXConstructorDecl>(GD.getDecl()) || (
+ isa<CXXDestructorDecl>(GD.getDecl()) &&
+ GD.getDtorType() != Dtor_Deleting));
+ }
void EmitReturnFromThunk(CodeGenFunction &CGF, RValue RV, QualType ResTy);
@@ -191,15 +182,6 @@
QualType ElementType);
llvm::Value *readArrayCookieImpl(CodeGenFunction &CGF, llvm::Value *allocPtr,
CharUnits cookieSize);
-
- /// \brief Returns true if the given instance method is one of the
- /// kinds that the ARM ABI says returns 'this'.
- bool HasThisReturn(GlobalDecl GD) const {
- const CXXMethodDecl *MD = dyn_cast_or_null<CXXMethodDecl>(GD.getDecl());
- if (!MD) return false;
- return ((isa<CXXDestructorDecl>(MD) && GD.getDtorType() != Dtor_Deleting) ||
- (isa<CXXConstructorDecl>(MD)));
- }
};
}
@@ -754,22 +736,14 @@
SmallVectorImpl<CanQualType> &ArgTys) {
ASTContext &Context = getContext();
- // 'this' is already there.
+ // 'this' parameter is already there, as well as 'this' return if
+ // HasThisReturn(GlobalDecl(Ctor, Type)) is true
// Check if we need to add a VTT parameter (which has type void **).
if (Type == Ctor_Base && Ctor->getParent()->getNumVBases() != 0)
ArgTys.push_back(Context.getPointerType(Context.VoidPtrTy));
}
-/// The ARM ABI does the same as the Itanium ABI, but returns 'this'.
-void ARMCXXABI::BuildConstructorSignature(const CXXConstructorDecl *Ctor,
- CXXCtorType Type,
- CanQualType &ResTy,
- SmallVectorImpl<CanQualType> &ArgTys) {
- ItaniumCXXABI::BuildConstructorSignature(Ctor, Type, ResTy, ArgTys);
- ResTy = ArgTys[0];
-}
-
/// The generic ABI passes 'this', plus a VTT if it's destroying a
/// base subobject.
void ItaniumCXXABI::BuildDestructorSignature(const CXXDestructorDecl *Dtor,
@@ -778,25 +752,14 @@
SmallVectorImpl<CanQualType> &ArgTys) {
ASTContext &Context = getContext();
- // 'this' is already there.
+ // 'this' parameter is already there, as well as 'this' return if
+ // HasThisReturn(GlobalDecl(Dtor, Type)) is true
// Check if we need to add a VTT parameter (which has type void **).
if (Type == Dtor_Base && Dtor->getParent()->getNumVBases() != 0)
ArgTys.push_back(Context.getPointerType(Context.VoidPtrTy));
}
-/// The ARM ABI does the same as the Itanium ABI, but returns 'this'
-/// for non-deleting destructors.
-void ARMCXXABI::BuildDestructorSignature(const CXXDestructorDecl *Dtor,
- CXXDtorType Type,
- CanQualType &ResTy,
- SmallVectorImpl<CanQualType> &ArgTys) {
- ItaniumCXXABI::BuildDestructorSignature(Dtor, Type, ResTy, ArgTys);
-
- if (Type != Dtor_Deleting)
- ResTy = ArgTys[0];
-}
-
void ItaniumCXXABI::BuildInstanceFunctionParams(CodeGenFunction &CGF,
QualType &ResTy,
FunctionArgList &Params) {
@@ -820,16 +783,6 @@
}
}
-void ARMCXXABI::BuildInstanceFunctionParams(CodeGenFunction &CGF,
- QualType &ResTy,
- FunctionArgList &Params) {
- ItaniumCXXABI::BuildInstanceFunctionParams(CGF, ResTy, Params);
-
- // Return 'this' from certain constructors and destructors.
- if (HasThisReturn(CGF.CurGD))
- ResTy = Params[0]->getType();
-}
-
void ItaniumCXXABI::EmitInstanceFunctionProlog(CodeGenFunction &CGF) {
/// Initialize the 'this' slot.
EmitThisParam(CGF);
@@ -840,21 +793,24 @@
= CGF.Builder.CreateLoad(CGF.GetAddrOfLocalVar(getVTTDecl(CGF)),
"vtt");
}
-}
-void ARMCXXABI::EmitInstanceFunctionProlog(CodeGenFunction &CGF) {
- ItaniumCXXABI::EmitInstanceFunctionProlog(CGF);
-
- /// Initialize the return slot to 'this' at the start of the
- /// function.
+ /// If this is a function that the ABI specifies returns 'this', initialize
+ /// the return slot to 'this' at the start of the function.
+ ///
+ /// Unlike the setting of return types, this is done within the ABI
+ /// implementation instead of by clients of CGCXXABI because:
+ /// 1) getThisValue is currently protected
+ /// 2) in theory, an ABI could implement 'this' returns some other way;
+ /// HasThisReturn only specifies a contract, not the implementation
if (HasThisReturn(CGF.CurGD))
CGF.Builder.CreateStore(getThisValue(CGF), CGF.ReturnValue);
}
-llvm::Value *ItaniumCXXABI::EmitConstructorCall(CodeGenFunction &CGF,
+RValue ItaniumCXXABI::EmitConstructorCall(CodeGenFunction &CGF,
const CXXConstructorDecl *D,
- CXXCtorType Type, bool ForVirtualBase,
- bool Delegating,
+ CXXCtorType Type,
+ bool ForVirtualBase, bool Delegating,
+ ReturnValueSlot ReturnValue,
llvm::Value *This,
CallExpr::const_arg_iterator ArgBeg,
CallExpr::const_arg_iterator ArgEnd) {
@@ -864,9 +820,8 @@
llvm::Value *Callee = CGM.GetAddrOfCXXConstructor(D, Type);
// FIXME: Provide a source location here.
- CGF.EmitCXXMemberCall(D, SourceLocation(), Callee, ReturnValueSlot(), This,
- VTT, VTTTy, ArgBeg, ArgEnd);
- return Callee;
+ return CGF.EmitCXXMemberCall(D, SourceLocation(), Callee, ReturnValue,
+ This, VTT, VTTTy, ArgBeg, ArgEnd);
}
RValue ItaniumCXXABI::EmitVirtualDestructorCall(CodeGenFunction &CGF,