Add a comment to clarify a magic constant
Hi rnk,
http://llvm-reviews.chandlerc.com/D1867
CHANGE SINCE LAST DIFF
http://llvm-reviews.chandlerc.com/D1867?vs=4758&id=4759#toc
Files:
lib/CodeGen/CGCXXABI.h
lib/CodeGen/CGClass.cpp
lib/CodeGen/MicrosoftCXXABI.cpp
test/CodeGenCXX/microsoft-abi-virtual-inheritance.cpp
Index: lib/CodeGen/CGCXXABI.h
===================================================================
--- lib/CodeGen/CGCXXABI.h
+++ lib/CodeGen/CGCXXABI.h
@@ -234,6 +234,12 @@
virtual llvm::BasicBlock *EmitCtorCompleteObjectHandler(CodeGenFunction &CGF,
const CXXRecordDecl *RD);
+ /// Emit the code to initialize hidden members required
+ /// to handle virtual inheritance, if needed by the ABI.
+ virtual void
+ initializeHiddenVirtualInheritanceMembers(CodeGenFunction &CGF,
+ const CXXRecordDecl *RD) {}
+
/// Emit constructor variants required by this ABI.
virtual void EmitCXXConstructors(const CXXConstructorDecl *D) = 0;
Index: lib/CodeGen/CGClass.cpp
===================================================================
--- lib/CodeGen/CGClass.cpp
+++ lib/CodeGen/CGClass.cpp
@@ -1992,6 +1992,8 @@
/*NearestVBase=*/0,
/*OffsetFromNearestVBase=*/CharUnits::Zero(),
/*BaseIsNonVirtualPrimaryBase=*/false, RD, VBases);
+
+ CGM.getCXXABI().initializeHiddenVirtualInheritanceMembers(*this, RD);
}
llvm::Value *CodeGenFunction::GetVTablePtr(llvm::Value *This,
Index: lib/CodeGen/MicrosoftCXXABI.cpp
===================================================================
--- lib/CodeGen/MicrosoftCXXABI.cpp
+++ lib/CodeGen/MicrosoftCXXABI.cpp
@@ -67,6 +67,9 @@
llvm::BasicBlock *EmitCtorCompleteObjectHandler(CodeGenFunction &CGF,
const CXXRecordDecl *RD);
+ void initializeHiddenVirtualInheritanceMembers(CodeGenFunction &CGF,
+ const CXXRecordDecl *RD);
+
void EmitCXXConstructors(const CXXConstructorDecl *D);
// Background on MSVC destructors
@@ -456,6 +459,51 @@
return SkipVbaseCtorsBB;
}
+void MicrosoftCXXABI::initializeHiddenVirtualInheritanceMembers(
+ CodeGenFunction &CGF, const CXXRecordDecl *RD) {
+ // In most cases, an override for a vbase virtual method can adjust
+ // the "this" parameter by applying a constant offset.
+ // However, this is not always enough when we execute a constructor or a
+ // destructor of some class X with virtual bases,
+ // X overrides a virtual method M of a vbase Y and
+ // X itself is a vbase of the most derived class.
+ // vtorDisp for vbase Y is a hidden member of X which holds the extra amount
+ // of "this" adjustment we must do when we use the X vftables
+ // (i.e. during X ctor or dtor).
+ // Outside the ctors and dtors, the values of vtorDisps are zero.
+ const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
+ typedef ASTRecordLayout::VBaseOffsetsMapTy VBOffsets;
+ const VBOffsets &VBaseMap = Layout.getVBaseOffsetsMap();
+ CGBuilderTy &Builder = CGF.Builder;
+
+ for (VBOffsets::const_iterator I = VBaseMap.begin(), E = VBaseMap.end();
+ I != E; ++I) {
+ if (!I->second.hasVtorDisp())
+ continue;
+
+ llvm::Value *VBaseOffset = CGM.getCXXABI().GetVirtualBaseClassOffset(
+ CGF, getThisValue(CGF), RD, I->first);
+ uint64_t ConstantVBaseOffset =
+ Layout.getVBaseClassOffset(I->first).getQuantity();
+ llvm::Value *VtorDispValue = Builder.CreateSub(
+ VBaseOffset, llvm::ConstantInt::get(CGM.IntPtrTy, ConstantVBaseOffset));
+
+ unsigned AS = cast<llvm::PointerType>(getThisValue(CGF)->getType())
+ ->getAddressSpace();
+ llvm::Value *Int8This =
+ Builder.CreateBitCast(getThisValue(CGF), CGF.Int8Ty->getPointerTo(AS));
+ llvm::Value *VtorDispPtr = Builder.CreateInBoundsGEP(Int8This, VBaseOffset);
+ // vtorDisp is always the 32-bits before the vbase in the class layout.
+ VtorDispPtr = Builder.CreateConstGEP1_32(VtorDispPtr, -4);
+ VtorDispPtr = Builder.CreateBitCast(
+ VtorDispPtr, CGF.Int32Ty->getPointerTo(AS), "vtordisp.ptr");
+ VtorDispValue = Builder.CreateTruncOrBitCast(VtorDispValue, CGF.Int32Ty,
+ "vtordisp.val");
+
+ Builder.CreateStore(VtorDispValue, VtorDispPtr);
+ }
+}
+
void MicrosoftCXXABI::EmitCXXConstructors(const CXXConstructorDecl *D) {
// There's only one constructor type in this ABI.
CGM.EmitGlobal(GlobalDecl(D, Ctor_Complete));
Index: test/CodeGenCXX/microsoft-abi-virtual-inheritance.cpp
===================================================================
--- test/CodeGenCXX/microsoft-abi-virtual-inheritance.cpp
+++ test/CodeGenCXX/microsoft-abi-virtual-inheritance.cpp
@@ -1,34 +1,85 @@
// RUN: %clang_cc1 %s -fno-rtti -cxx-abi microsoft -triple=i386-pc-win32 -emit-llvm -o - | FileCheck %s
+// For now, just make sure x86_64 doesn't crash.
+// RUN: %clang_cc1 %s -fno-rtti -cxx-abi microsoft -triple=x86_64-pc-win32 -emit-llvm -o %t
+
struct VBase {
+ virtual ~VBase();
virtual void foo();
virtual void bar();
int field;
};
struct B : virtual VBase {
B();
+ virtual ~B();
virtual void foo();
virtual void bar();
};
B::B() {
- // CHECK: @"\01??0B@@QAE@XZ"
+ // CHECK-LABEL: define x86_thiscallcc %struct.B* @"\01??0B@@QAE@XZ"
// CHECK: %[[THIS:.*]] = load %struct.B**
// CHECK: br i1 %{{.*}}, label %[[INIT_VBASES:.*]], label %[[SKIP_VBASES:.*]]
+
+ // Don't check the INIT_VBASES case as it's covered by the ctor tests.
+
// CHECK: %[[SKIP_VBASES]]
// CHECK: %[[THIS_i8:.*]] = bitcast %struct.B* %[[THIS]] to i8*
// CHECK: %[[VBPTR:.*]] = getelementptr inbounds i8* %[[THIS_i8]], i32 0
+ // ...
// CHECK: %[[THIS_i8:.*]] = bitcast %struct.B* %[[THIS]] to i8*
// CHECK: %[[VFPTR_i8:.*]] = getelementptr inbounds i8* %[[THIS_i8]], i32 %{{.*}}
- // CHECK: %[[VFPTR:.*]] = bitcast i8* %[[VFPTR_i8]] to [2 x i8*]**
- // CHECK: store [2 x i8*]* @"\01??_7B@@6B@", [2 x i8*]** %[[VFPTR]]
- // FIXME: Should initialize the vtorDisp here.
+ // CHECK: %[[VFPTR:.*]] = bitcast i8* %[[VFPTR_i8]] to [3 x i8*]**
+ // CHECK: store [3 x i8*]* @"\01??_7B@@6B@", [3 x i8*]** %[[VFPTR]]
+
+ // Initialize vtorDisp:
+ // CHECK: %[[THIS_i8:.*]] = bitcast %struct.B* %[[THIS]] to i8*
+ // CHECK: %[[VBPTR:.*]] = getelementptr inbounds i8* %[[THIS_i8]], i32 0
+ // ...
+ // CHECK: %[[VBASE_OFFSET:.*]] = add nsw i32 0, %{{.*}}
+ // CHECK: %[[VTORDISP_VAL:.*]] = sub i32 %[[VBASE_OFFSET]], 8
+ // CHECK: %[[THIS_i8:.*]] = bitcast %struct.B* %[[THIS]] to i8*
+ // CHECK: %[[VBASE_i8:.*]] = getelementptr inbounds i8* %[[THIS_i8]], i32 %[[VBASE_OFFSET]]
+ // CHECK: %[[VTORDISP_i8:.*]] = getelementptr i8* %[[VBASE_i8]], i32 -4
+ // CHECK: %[[VTORDISP_PTR:.*]] = bitcast i8* %[[VTORDISP_i8]] to i32*
+ // CHECK: store i32 %[[VTORDISP_VAL]], i32* %[[VTORDISP_PTR]]
+
+ // CHECK: ret
+}
+
+B::~B() {
+ // CHECK-LABEL: define x86_thiscallcc void @"\01??1B@@UAE@XZ"
+ // CHECK: %[[THIS:.*]] = load %struct.B**
+
+ // Restore the vfptr that could have been changed by a subclass.
+ // CHECK: %[[THIS_i8:.*]] = bitcast %struct.B* %[[THIS]] to i8*
+ // CHECK: %[[VBPTR:.*]] = getelementptr inbounds i8* %[[THIS_i8]], i32 0
+ // ...
+ // CHECK: %[[THIS_i8:.*]] = bitcast %struct.B* %[[THIS]] to i8*
+ // CHECK: %[[VFPTR_i8:.*]] = getelementptr inbounds i8* %[[THIS_i8]], i32 %{{.*}}
+ // CHECK: %[[VFPTR:.*]] = bitcast i8* %[[VFPTR_i8]] to [3 x i8*]**
+ // CHECK: store [3 x i8*]* @"\01??_7B@@6B@", [3 x i8*]** %[[VFPTR]]
+
+ // Initialize vtorDisp:
+ // CHECK: %[[THIS_i8:.*]] = bitcast %struct.B* %[[THIS]] to i8*
+ // CHECK: %[[VBPTR:.*]] = getelementptr inbounds i8* %[[THIS_i8]], i32 0
+ // ...
+ // CHECK: %[[VBASE_OFFSET:.*]] = add nsw i32 0, %{{.*}}
+ // CHECK: %[[VTORDISP_VAL:.*]] = sub i32 %[[VBASE_OFFSET]], 8
+ // CHECK: %[[THIS_i8:.*]] = bitcast %struct.B* %[[THIS]] to i8*
+ // CHECK: %[[VBASE_i8:.*]] = getelementptr inbounds i8* %[[THIS_i8]], i32 %[[VBASE_OFFSET]]
+ // CHECK: %[[VTORDISP_i8:.*]] = getelementptr i8* %[[VBASE_i8]], i32 -4
+ // CHECK: %[[VTORDISP_PTR:.*]] = bitcast i8* %[[VTORDISP_i8]] to i32*
+ // CHECK: store i32 %[[VTORDISP_VAL]], i32* %[[VTORDISP_PTR]]
+
+ foo(); // Avoid the "trivial destructor" optimization.
+
// CHECK: ret
}
void B::foo() {
-// CHECK: define x86_thiscallcc void @"\01?foo@B@@UAEXXZ"(i8*
+// CHECK-LABEL: define x86_thiscallcc void @"\01?foo@B@@UAEXXZ"(i8*
//
// B::foo gets 'this' cast to VBase* in ECX (i.e. this+8) so we
// need to adjust 'this' before use.
@@ -58,7 +109,7 @@
}
void call_vbase_bar(B *obj) {
-// CHECK: define void @"\01?call_vbase_bar@@YAXPAUB@@@Z"(%struct.B* %obj)
+// CHECK-LABEL: define void @"\01?call_vbase_bar@@YAXPAUB@@@Z"(%struct.B* %obj)
// CHECK: %[[OBJ:.*]] = load %struct.B
obj->bar();
@@ -76,7 +127,7 @@
// CHECK: %[[VBASE_i8:.*]] = getelementptr inbounds i8* %[[OBJ_i8]], i32 %[[VBOFFSET]]
// CHECK: %[[VFPTR:.*]] = bitcast i8* %[[VBASE_i8]] to void (i8*)***
// CHECK: %[[VFTABLE:.*]] = load void (i8*)*** %[[VFPTR]]
-// CHECK: %[[VFUN:.*]] = getelementptr inbounds void (i8*)** %[[VFTABLE]], i64 1
+// CHECK: %[[VFUN:.*]] = getelementptr inbounds void (i8*)** %[[VFTABLE]], i64 2
// CHECK: %[[VFUN_VALUE:.*]] = load void (i8*)** %[[VFUN]]
//
// CHECK: %[[OBJ_i8:.*]] = bitcast %struct.B* %[[OBJ]] to i8*
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