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[clang] Add cc1 option -fctor-dtor-return-this
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This option forces constructors and non-deleting destructors to return
`this` pointer in C++ ABI (except for Microsoft ABI, on which this flag
has no effect).

This is similar to ARM32, Apple ARM64, or Fuchsia C++ ABI, but can be
applied to any target triple.

Differential Revision: https://reviews.llvm.org/D119209
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@scweng
scweng committed Oct 3, 2022
1 parent 4247cdb commit 3933c43
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Showing 5 changed files with 64 additions and 35 deletions.
4 changes: 4 additions & 0 deletions clang/include/clang/Basic/CodeGenOptions.def
View file
Expand Up @@ -492,6 +492,10 @@ ENUM_CODEGENOPT(ZeroCallUsedRegs, llvm::ZeroCallUsedRegs::ZeroCallUsedRegsKind,
/// Whether to use opaque pointers.
CODEGENOPT(OpaquePointers, 1, 0)

/// Modify C++ ABI to returning `this` pointer from constructors and
/// non-deleting destructors. (No effect on Microsoft ABI.)
CODEGENOPT(CtorDtorReturnThis, 1, 0)

#undef CODEGENOPT
#undef ENUM_CODEGENOPT
#undef VALUE_CODEGENOPT
5 changes: 5 additions & 0 deletions clang/include/clang/Driver/Options.td
View file
Expand Up @@ -5604,6 +5604,11 @@ def ehcontguard : Flag<["-"], "ehcontguard">,
def fdenormal_fp_math_f32_EQ : Joined<["-"], "fdenormal-fp-math-f32=">,
Group<f_Group>;

def fctor_dtor_return_this : Flag<["-"], "fctor-dtor-return-this">,
HelpText<"Change the C++ ABI to returning `this` pointer from constructors "
"and non-deleting destructors. (No effect on Microsoft ABI)">,
MarshallingInfoFlag<CodeGenOpts<"CtorDtorReturnThis">>;

} // let Flags = [CC1Option, NoDriverOption]

//===----------------------------------------------------------------------===//
Expand Down
12 changes: 11 additions & 1 deletion clang/lib/CodeGen/CGCXXABI.h
View file
Expand Up @@ -105,6 +105,10 @@ class CGCXXABI {
/// final class will have been taken care of by the caller.
virtual bool isThisCompleteObject(GlobalDecl GD) const = 0;

virtual bool constructorsAndDestructorsReturnThis() const {
return CGM.getCodeGenOpts().CtorDtorReturnThis;
}

public:

virtual ~CGCXXABI();
Expand All @@ -120,7 +124,13 @@ class CGCXXABI {
///
/// There currently is no way to indicate if a destructor returns 'this'
/// when called virtually, and code generation does not support the case.
virtual bool HasThisReturn(GlobalDecl GD) const { return false; }
virtual bool HasThisReturn(GlobalDecl GD) const {
if (isa<CXXConstructorDecl>(GD.getDecl()) ||
(isa<CXXDestructorDecl>(GD.getDecl()) &&
GD.getDtorType() != Dtor_Deleting))
return constructorsAndDestructorsReturnThis();
return false;
}

virtual bool hasMostDerivedReturn(GlobalDecl GD) const { return false; }

Expand Down
18 changes: 3 additions & 15 deletions clang/lib/CodeGen/ItaniumCXXABI.cpp
View file
Expand Up @@ -433,11 +433,7 @@ class ARMCXXABI : public ItaniumCXXABI {
ItaniumCXXABI(CGM, /*UseARMMethodPtrABI=*/true,
/*UseARMGuardVarABI=*/true) {}

bool HasThisReturn(GlobalDecl GD) const override {
return (isa<CXXConstructorDecl>(GD.getDecl()) || (
isa<CXXDestructorDecl>(GD.getDecl()) &&
GD.getDtorType() != Dtor_Deleting));
}
bool constructorsAndDestructorsReturnThis() const override { return true; }

void EmitReturnFromThunk(CodeGenFunction &CGF, RValue RV,
QualType ResTy) override;
Expand Down Expand Up @@ -468,11 +464,7 @@ class FuchsiaCXXABI final : public ItaniumCXXABI {
: ItaniumCXXABI(CGM) {}

private:
bool HasThisReturn(GlobalDecl GD) const override {
return isa<CXXConstructorDecl>(GD.getDecl()) ||
(isa<CXXDestructorDecl>(GD.getDecl()) &&
GD.getDtorType() != Dtor_Deleting);
}
bool constructorsAndDestructorsReturnThis() const override { return true; }
};

class WebAssemblyCXXABI final : public ItaniumCXXABI {
Expand All @@ -486,11 +478,7 @@ class WebAssemblyCXXABI final : public ItaniumCXXABI {
llvm::Value *Exn) override;

private:
bool HasThisReturn(GlobalDecl GD) const override {
return isa<CXXConstructorDecl>(GD.getDecl()) ||
(isa<CXXDestructorDecl>(GD.getDecl()) &&
GD.getDtorType() != Dtor_Deleting);
}
bool constructorsAndDestructorsReturnThis() const override { return true; }
bool canCallMismatchedFunctionType() const override { return false; }
};

Expand Down
60 changes: 41 additions & 19 deletions clang/test/CodeGenCXX/constructor-destructor-return-this.cpp
View file
Expand Up @@ -6,6 +6,8 @@
//RUN: %clang_cc1 -no-opaque-pointers %s -emit-llvm -o - -triple=x86_64-unknown-fuchsia | FileCheck --check-prefix=CHECKFUCHSIA %s
//RUN: %clang_cc1 -no-opaque-pointers %s -emit-llvm -o - -triple=aarch64-unknown-fuchsia | FileCheck --check-prefix=CHECKFUCHSIA %s
//RUN: %clang_cc1 -no-opaque-pointers %s -emit-llvm -o - -triple=i386-pc-win32 -fno-rtti | FileCheck --check-prefix=CHECKMS %s
//RUN: %clang_cc1 -no-opaque-pointers %s -emit-llvm -o - -triple=i686-unknown-linux-gnu -fctor-dtor-return-this | FileCheck --check-prefix=CHECKI686RET %s
//RUN: %clang_cc1 -no-opaque-pointers %s -emit-llvm -o - -triple=aarch64-unknown-linux-gnu -fctor-dtor-return-this | FileCheck --check-prefix=CHECKAARCH64RET %s
// FIXME: these tests crash on the bots when run with -triple=x86_64-pc-win32

// Make sure we attach the 'returned' attribute to the 'this' parameter of
Expand Down Expand Up @@ -37,10 +39,15 @@ B::~B() { }
// CHECKGEN-LABEL: define{{.*}} void @_ZN1BD2Ev(%class.B* {{[^,]*}} %this)
// CHECKGEN-LABEL: define{{.*}} void @_ZN1BD1Ev(%class.B* {{[^,]*}} %this)

// CHECKARM-LABEL: define{{.*}} %class.B* @_ZN1BC2EPi(%class.B* {{[^,]*}} returned{{[^,]*}} %this, i32* noundef %i)
// CHECKARM-LABEL: define{{.*}} %class.B* @_ZN1BC1EPi(%class.B* {{[^,]*}} returned{{[^,]*}} %this, i32* noundef %i)
// CHECKARM-LABEL: define{{.*}} %class.B* @_ZN1BD2Ev(%class.B* {{[^,]*}} returned{{[^,]*}} %this)
// CHECKARM-LABEL: define{{.*}} %class.B* @_ZN1BD1Ev(%class.B* {{[^,]*}} returned{{[^,]*}} %this)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.B* @_ZN1BC2EPi(%class.B* {{[^,]*}} returned{{[^,]*}} %this, i32* noundef %i)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.B* @_ZN1BC1EPi(%class.B* {{[^,]*}} returned{{[^,]*}} %this, i32* noundef %i)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.B* @_ZN1BD2Ev(%class.B* {{[^,]*}} returned{{[^,]*}} %this)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.B* @_ZN1BD1Ev(%class.B* {{[^,]*}} returned{{[^,]*}} %this)

// CHECKI686RET-LABEL: define{{.*}} %class.B* @_ZN1BC2EPi(%class.B* {{[^,]*}} %this, i32* noundef %i)
// CHECKI686RET-LABEL: define{{.*}} %class.B* @_ZN1BC1EPi(%class.B* {{[^,]*}} %this, i32* noundef %i)
// CHECKI686RET-LABEL: define{{.*}} %class.B* @_ZN1BD2Ev(%class.B* {{[^,]*}} %this)
// CHECKI686RET-LABEL: define{{.*}} %class.B* @_ZN1BD1Ev(%class.B* {{[^,]*}} %this)

// CHECKIOS5-LABEL: define{{.*}} %class.B* @_ZN1BC2EPi(%class.B* {{[^,]*}} %this, i32* noundef %i)
// CHECKIOS5-LABEL: define{{.*}} %class.B* @_ZN1BC1EPi(%class.B* {{[^,]*}} %this, i32* noundef %i)
Expand Down Expand Up @@ -74,13 +81,23 @@ C::~C() { }
// CHECKGEN-LABEL: define{{.*}} void @_ZN1CD0Ev(%class.C* {{[^,]*}} %this)
// CHECKGEN-LABEL: define{{.*}} void @_ZThn8_N1CD0Ev(%class.C* noundef %this)

// CHECKARM-LABEL: define{{.*}} %class.C* @_ZN1CC2EPiPc(%class.C* {{[^,]*}} returned{{[^,]*}} %this, i32* noundef %i, i8* noundef %c)
// CHECKARM-LABEL: define{{.*}} %class.C* @_ZN1CC1EPiPc(%class.C* {{[^,]*}} returned{{[^,]*}} %this, i32* noundef %i, i8* noundef %c)
// CHECKARM-LABEL: define{{.*}} %class.C* @_ZN1CD2Ev(%class.C* {{[^,]*}} returned{{[^,]*}} %this)
// CHECKARM-LABEL: define{{.*}} %class.C* @_ZN1CD1Ev(%class.C* {{[^,]*}} returned{{[^,]*}} %this)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.C* @_ZN1CC2EPiPc(%class.C* {{[^,]*}} returned{{[^,]*}} %this, i32* noundef %i, i8* noundef %c)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.C* @_ZN1CC1EPiPc(%class.C* {{[^,]*}} returned{{[^,]*}} %this, i32* noundef %i, i8* noundef %c)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.C* @_ZN1CD2Ev(%class.C* {{[^,]*}} returned{{[^,]*}} %this)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.C* @_ZN1CD1Ev(%class.C* {{[^,]*}} returned{{[^,]*}} %this)
// CHECKARM-LABEL: define{{.*}} %class.C* @_ZThn8_N1CD1Ev(%class.C* noundef %this)
// CHECKARM-LABEL: define{{.*}} void @_ZN1CD0Ev(%class.C* {{[^,]*}} %this)
// CHECKAARCH64RET-LABEL: define{{.*}} %class.C* @_ZThn16_N1CD1Ev(%class.C* noundef %this)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} void @_ZN1CD0Ev(%class.C* {{[^,]*}} %this)
// CHECKARM-LABEL: define{{.*}} void @_ZThn8_N1CD0Ev(%class.C* noundef %this)
// CHECKAARCH64RET-LABEL: define{{.*}} void @_ZThn16_N1CD0Ev(%class.C* noundef %this)

// CHECKI686RET-LABEL: define{{.*}} %class.C* @_ZN1CC2EPiPc(%class.C* {{[^,]*}} %this, i32* noundef %i, i8* noundef %c)
// CHECKI686RET-LABEL: define{{.*}} %class.C* @_ZN1CC1EPiPc(%class.C* {{[^,]*}} %this, i32* noundef %i, i8* noundef %c)
// CHECKI686RET-LABEL: define{{.*}} %class.C* @_ZN1CD2Ev(%class.C* {{[^,]*}} %this)
// CHECKI686RET-LABEL: define{{.*}} %class.C* @_ZN1CD1Ev(%class.C* {{[^,]*}} %this)
// CHECKI686RET-LABEL: define{{.*}} %class.C* @_ZThn8_N1CD1Ev(%class.C* noundef %this)
// CHECKI686RET-LABEL: define{{.*}} void @_ZN1CD0Ev(%class.C* {{[^,]*}} %this)
// CHECKI686RET-LABEL: define{{.*}} void @_ZThn8_N1CD0Ev(%class.C* noundef %this)

// CHECKIOS5-LABEL: define{{.*}} %class.C* @_ZN1CC2EPiPc(%class.C* {{[^,]*}} %this, i32* noundef %i, i8* noundef %c)
// CHECKIOS5-LABEL: define{{.*}} %class.C* @_ZN1CC1EPiPc(%class.C* {{[^,]*}} %this, i32* noundef %i, i8* noundef %c)
Expand Down Expand Up @@ -115,10 +132,15 @@ D::~D() { }
// CHECKGEN-LABEL: define{{.*}} void @_ZN1DD2Ev(%class.D* {{[^,]*}} %this, i8** noundef %vtt)
// CHECKGEN-LABEL: define{{.*}} void @_ZN1DD1Ev(%class.D* {{[^,]*}} %this)

// CHECKARM-LABEL: define{{.*}} %class.D* @_ZN1DC2Ev(%class.D* {{[^,]*}} returned{{[^,]*}} %this, i8** noundef %vtt)
// CHECKARM-LABEL: define{{.*}} %class.D* @_ZN1DC1Ev(%class.D* {{[^,]*}} returned{{[^,]*}} %this)
// CHECKARM-LABEL: define{{.*}} %class.D* @_ZN1DD2Ev(%class.D* {{[^,]*}} returned{{[^,]*}} %this, i8** noundef %vtt)
// CHECKARM-LABEL: define{{.*}} %class.D* @_ZN1DD1Ev(%class.D* {{[^,]*}} returned{{[^,]*}} %this)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.D* @_ZN1DC2Ev(%class.D* {{[^,]*}} returned{{[^,]*}} %this, i8** noundef %vtt)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.D* @_ZN1DC1Ev(%class.D* {{[^,]*}} returned{{[^,]*}} %this)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.D* @_ZN1DD2Ev(%class.D* {{[^,]*}} returned{{[^,]*}} %this, i8** noundef %vtt)
// CHECKARM-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} %class.D* @_ZN1DD1Ev(%class.D* {{[^,]*}} returned{{[^,]*}} %this)

// CHECKI686RET-LABEL: define{{.*}} %class.D* @_ZN1DC2Ev(%class.D* {{[^,]*}} %this, i8** noundef %vtt)
// CHECKI686RET-LABEL: define{{.*}} %class.D* @_ZN1DC1Ev(%class.D* {{[^,]*}} %this)
// CHECKI686RET-LABEL: define{{.*}} %class.D* @_ZN1DD2Ev(%class.D* {{[^,]*}} %this, i8** noundef %vtt)
// CHECKI686RET-LABEL: define{{.*}} %class.D* @_ZN1DD1Ev(%class.D* {{[^,]*}} %this)

// CHECKIOS5-LABEL: define{{.*}} %class.D* @_ZN1DC2Ev(%class.D* {{[^,]*}} %this, i8** noundef %vtt)
// CHECKIOS5-LABEL: define{{.*}} %class.D* @_ZN1DC1Ev(%class.D* {{[^,]*}} %this)
Expand Down Expand Up @@ -147,17 +169,17 @@ void test_destructor() {
e2->~E();
}

// CHECKARM-LABEL,CHECKFUCHSIA-LABEL: define{{.*}} void @_Z15test_destructorv()
// CHECKARM-LABEL,CHECKFUCHSIA-LABEL,CHECKAARCH64RET-LABEL: define{{.*}} void @_Z15test_destructorv()

// Verify that virtual calls to destructors are not marked with a 'returned'
// this parameter at the call site...
// CHECKARM: [[VFN:%.*]] = getelementptr inbounds %class.E* (%class.E*)*, %class.E* (%class.E*)**
// CHECKARM: [[THUNK:%.*]] = load %class.E* (%class.E*)*, %class.E* (%class.E*)** [[VFN]]
// CHECKARM,CHECKAARCH64RET: [[VFN:%.*]] = getelementptr inbounds %class.E* (%class.E*)*, %class.E* (%class.E*)**
// CHECKARM,CHECKAARCH64RET: [[THUNK:%.*]] = load %class.E* (%class.E*)*, %class.E* (%class.E*)** [[VFN]]
// CHECKFUCHSIA: [[THUNK_I8:%.*]] = call i8* @llvm.load.relative.i32(i8* {{.*}}, i32 0)
// CHECKFUCHSIA: [[THUNK:%.*]] = bitcast i8* [[THUNK_I8]] to %class.E* (%class.E*)*
// CHECKARM,CHECKFUCHSIA: call noundef %class.E* [[THUNK]](%class.E* {{[^,]*}} %
// CHECKARM,CHECKFUCHSIA,CHECKAARCH64RET: call noundef %class.E* [[THUNK]](%class.E* {{[^,]*}} %

// ...but static calls create declarations with 'returned' this
// CHECKARM,CHECKFUCHSIA: {{%.*}} = call noundef %class.E* @_ZN1ED1Ev(%class.E* {{[^,]*}} %
// CHECKARM,CHECKFUCHSIA,CHECKAARCH64RET: {{%.*}} = call noundef %class.E* @_ZN1ED1Ev(%class.E* {{[^,]*}} %

// CHECKARM,CHECKFUCHSIA: declare noundef %class.E* @_ZN1ED1Ev(%class.E* {{[^,]*}} returned{{[^,]*}})
// CHECKARM,CHECKFUCHSIA,CHECKAARCH64RET: declare noundef %class.E* @_ZN1ED1Ev(%class.E* {{[^,]*}} returned{{[^,]*}})

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