[CIR] Add support for initializing classes with multiple vtables #155275
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@llvm/pr-subscribers-clang @llvm/pr-subscribers-clangir Author: Andy Kaylor (andykaylor) ChangesThis adds support for initializing the vptr members in a class that requires multiple vtables because of multiple inheritence. This still does not handle virtual bases. Full diff: https://github.com/llvm/llvm-project/pull/155275.diff 3 Files Affected:
diff --git a/clang/lib/CIR/CodeGen/CIRGenClass.cpp b/clang/lib/CIR/CodeGen/CIRGenClass.cpp
index 3e5dc22426d8e..26d6447480750 100644
--- a/clang/lib/CIR/CodeGen/CIRGenClass.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenClass.cpp
@@ -14,6 +14,7 @@
#include "CIRGenFunction.h"
#include "CIRGenValue.h"
+#include "clang/AST/EvaluatedExprVisitor.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/RecordLayout.h"
#include "clang/AST/Type.h"
@@ -126,6 +127,32 @@ static bool isInitializerOfDynamicClass(const CXXCtorInitializer *baseInit) {
return baseClassDecl->isDynamicClass();
}
+namespace {
+/// A visitor which checks whether an initializer uses 'this' in a
+/// way which requires the vtable to be properly set.
+struct DynamicThisUseChecker
+ : ConstEvaluatedExprVisitor<DynamicThisUseChecker> {
+ using super = ConstEvaluatedExprVisitor<DynamicThisUseChecker>;
+
+ bool usesThis;
+
+ DynamicThisUseChecker(const ASTContext &c) : super(c), usesThis(false) {}
+
+ // Black-list all explicit and implicit references to 'this'.
+ //
+ // Do we need to worry about external references to 'this' derived
+ // from arbitrary code? If so, then anything which runs arbitrary
+ // external code might potentially access the vtable.
+ void VisitCXXThisExpr(const CXXThisExpr *e) { usesThis = true; }
+};
+} // end anonymous namespace
+
+static bool baseInitializerUsesThis(ASTContext &c, const Expr *init) {
+ DynamicThisUseChecker checker(c);
+ checker.Visit(init);
+ return checker.usesThis;
+}
+
/// Gets the address of a direct base class within a complete object.
/// This should only be used for (1) non-virtual bases or (2) virtual bases
/// when the type is known to be complete (e.g. in complete destructors).
@@ -170,10 +197,8 @@ void CIRGenFunction::emitBaseInitializer(mlir::Location loc,
// If the initializer for the base (other than the constructor
// itself) accesses 'this' in any way, we need to initialize the
// vtables.
- if (classDecl->isDynamicClass()) {
- cgm.errorNYI(loc, "emitBaseInitializer: dynamic class");
- return;
- }
+ if (baseInitializerUsesThis(getContext(), baseInit->getInit()))
+ initializeVTablePointers(loc, classDecl);
// We can pretend to be a complete class because it only matters for
// virtual bases, and we only do virtual bases for complete ctors.
@@ -264,6 +289,37 @@ void CIRGenFunction::emitCtorPrologue(const CXXConstructorDecl *cd,
}
}
+static Address applyNonVirtualAndVirtualOffset(
+ mlir::Location loc, CIRGenFunction &cgf, Address addr,
+ CharUnits nonVirtualOffset, mlir::Value virtualOffset,
+ const CXXRecordDecl *derivedClass, const CXXRecordDecl *nearestVBase,
+ mlir::Type baseValueTy = {}, bool assumeNotNull = true) {
+ // Assert that we have something to do.
+ assert(!nonVirtualOffset.isZero() || virtualOffset != nullptr);
+
+ // Compute the offset from the static and dynamic components.
+ mlir::Value baseOffset;
+ if (!nonVirtualOffset.isZero()) {
+ if (virtualOffset) {
+ cgf.cgm.errorNYI(
+ loc,
+ "applyNonVirtualAndVirtualOffset: virtual and non-virtual offset");
+ return Address::invalid();
+ } else {
+ assert(baseValueTy && "expected base type");
+ // If no virtualOffset is present this is the final stop.
+ return cgf.getBuilder().createBaseClassAddr(
+ loc, addr, baseValueTy, nonVirtualOffset.getQuantity(),
+ assumeNotNull);
+ }
+ } else {
+ baseOffset = virtualOffset;
+ }
+
+ cgf.cgm.errorNYI(loc, "applyNonVirtualAndVirtualOffset: virtual offset");
+ return Address::invalid();
+}
+
void CIRGenFunction::initializeVTablePointer(mlir::Location loc,
const VPtr &vptr) {
// Compute the address point.
@@ -291,8 +347,9 @@ void CIRGenFunction::initializeVTablePointer(mlir::Location loc,
// Apply the offsets.
Address classAddr = loadCXXThisAddress();
if (!nonVirtualOffset.isZero() || virtualOffset) {
- cgm.errorNYI(loc,
- "initializeVTablePointer: non-virtual and virtual offset");
+ classAddr = applyNonVirtualAndVirtualOffset(
+ loc, *this, classAddr, nonVirtualOffset, virtualOffset,
+ vptr.vtableClass, vptr.nearestVBase, baseValueTy);
}
// Finally, store the address point. Use the same CIR types as the field.
@@ -326,10 +383,11 @@ void CIRGenFunction::initializeVTablePointers(mlir::Location loc,
CIRGenFunction::VPtrsVector
CIRGenFunction::getVTablePointers(const CXXRecordDecl *vtableClass) {
CIRGenFunction::VPtrsVector vptrsResult;
+ VisitedVirtualBasesSetTy vbases;
getVTablePointers(BaseSubobject(vtableClass, CharUnits::Zero()),
/*NearestVBase=*/nullptr,
/*OffsetFromNearestVBase=*/CharUnits::Zero(),
- /*BaseIsNonVirtualPrimaryBase=*/false, vtableClass,
+ /*BaseIsNonVirtualPrimaryBase=*/false, vtableClass, vbases,
vptrsResult);
return vptrsResult;
}
@@ -339,6 +397,7 @@ void CIRGenFunction::getVTablePointers(BaseSubobject base,
CharUnits offsetFromNearestVBase,
bool baseIsNonVirtualPrimaryBase,
const CXXRecordDecl *vtableClass,
+ VisitedVirtualBasesSetTy &vbases,
VPtrsVector &vptrs) {
// If this base is a non-virtual primary base the address point has already
// been set.
@@ -350,8 +409,39 @@ void CIRGenFunction::getVTablePointers(BaseSubobject base,
const CXXRecordDecl *rd = base.getBase();
- if (rd->getNumBases())
- cgm.errorNYI(rd->getSourceRange(), "getVTablePointers: traverse bases");
+ for (const auto &nextBase : rd->bases()) {
+ const auto *baseDecl =
+ cast<CXXRecordDecl>(
+ nextBase.getType()->castAs<RecordType>()->getOriginalDecl())
+ ->getDefinitionOrSelf();
+
+ // Ignore classes without a vtable.
+ if (!baseDecl->isDynamicClass())
+ continue;
+
+ CharUnits baseOffset;
+ CharUnits baseOffsetFromNearestVBase;
+ bool baseDeclIsNonVirtualPrimaryBase;
+ const CXXRecordDecl *nextBaseDecl;
+
+ if (nextBase.isVirtual()) {
+ cgm.errorNYI(rd->getSourceRange(), "getVTablePointers: virtual base");
+ return;
+ } else {
+ const ASTRecordLayout &layout = getContext().getASTRecordLayout(rd);
+
+ nextBaseDecl = baseDecl;
+ baseOffset = base.getBaseOffset() + layout.getBaseClassOffset(baseDecl);
+ baseOffsetFromNearestVBase =
+ offsetFromNearestVBase + layout.getBaseClassOffset(baseDecl);
+ baseDeclIsNonVirtualPrimaryBase = layout.getPrimaryBase() == baseDecl;
+ }
+
+ getVTablePointers(BaseSubobject(baseDecl, baseOffset), nextBaseDecl,
+ baseOffsetFromNearestVBase,
+ baseDeclIsNonVirtualPrimaryBase, vtableClass, vbases,
+ vptrs);
+ }
}
Address CIRGenFunction::loadCXXThisAddress() {
diff --git a/clang/lib/CIR/CodeGen/CIRGenFunction.h b/clang/lib/CIR/CodeGen/CIRGenFunction.h
index 064b3c15a310b..c799ecdc27538 100644
--- a/clang/lib/CIR/CodeGen/CIRGenFunction.h
+++ b/clang/lib/CIR/CodeGen/CIRGenFunction.h
@@ -574,6 +574,9 @@ class CIRGenFunction : public CIRGenTypeCache {
const clang::CXXRecordDecl *vtableClass;
};
+ using VisitedVirtualBasesSetTy =
+ llvm::SmallPtrSet<const clang::CXXRecordDecl *, 4>;
+
using VPtrsVector = llvm::SmallVector<VPtr, 4>;
VPtrsVector getVTablePointers(const clang::CXXRecordDecl *vtableClass);
void getVTablePointers(clang::BaseSubobject base,
@@ -581,7 +584,7 @@ class CIRGenFunction : public CIRGenTypeCache {
clang::CharUnits offsetFromNearestVBase,
bool baseIsNonVirtualPrimaryBase,
const clang::CXXRecordDecl *vtableClass,
- VPtrsVector &vptrs);
+ VisitedVirtualBasesSetTy &vbases, VPtrsVector &vptrs);
/// Return the Value of the vtable pointer member pointed to by thisAddr.
mlir::Value getVTablePtr(mlir::Location loc, Address thisAddr,
const clang::CXXRecordDecl *vtableClass);
diff --git a/clang/test/CIR/CodeGen/multi-vtable.cpp b/clang/test/CIR/CodeGen/multi-vtable.cpp
index c127285800844..b42f8a6518095 100644
--- a/clang/test/CIR/CodeGen/multi-vtable.cpp
+++ b/clang/test/CIR/CodeGen/multi-vtable.cpp
@@ -22,6 +22,7 @@ class Father {
class Child : public Mother, public Father {
public:
+ Child();
void MotherKey() override;
};
@@ -36,6 +37,50 @@ void Child::MotherKey() {}
// CIR-DAG: !rec_Mother = !cir.record<class "Mother" {!cir.vptr}
// CIR-DAG: !rec_Child = !cir.record<class "Child" {!rec_Mother, !rec_Father}
+// Child vtable
+
+// CIR: cir.global "private" external @_ZTV5Child = #cir.vtable<{
+// CIR-SAME: #cir.const_array<[
+// CIR-SAME: #cir.ptr<null> : !cir.ptr<!u8i>,
+// CIR-SAME: #cir.ptr<null> : !cir.ptr<!u8i>,
+// CIR-SAME: #cir.global_view<@_ZN5Child9MotherKeyEv> : !cir.ptr<!u8i>,
+// CIR-SAME: #cir.global_view<@_ZN6Mother12MotherNonKeyEv> : !cir.ptr<!u8i>
+// CIR-SAME: ]> : !cir.array<!cir.ptr<!u8i> x 4>,
+// CIR-SAME: #cir.const_array<[
+// CIR-SAME: #cir.ptr<-8 : i64> : !cir.ptr<!u8i>,
+// CIR-SAME: #cir.ptr<null> : !cir.ptr<!u8i>,
+// CIR-SAME: #cir.global_view<@_ZN6Father9FatherKeyEv> : !cir.ptr<!u8i>
+// CIR-SAME: ]> : !cir.array<!cir.ptr<!u8i> x 3>
+// CIR-SAME: }> : [[CHILD_VTABLE_TYPE]]
+
+// LLVM: @_ZTV5Child = global { [4 x ptr], [3 x ptr] } {
+// LLVM-SAME: [4 x ptr] [
+// LLVM-SAME: ptr null,
+// LLVM-SAME: ptr null,
+// LLVM-SAME: ptr @_ZN5Child9MotherKeyEv,
+// LLVM-SAME: ptr @_ZN6Mother12MotherNonKeyEv
+// LLVM-SAME: ],
+// LLVM-SAME: [3 x ptr] [
+// LLVM-SAME: ptr inttoptr (i64 -8 to ptr),
+// LLVM-SAME: ptr null,
+// LLVM-SAME: ptr @_ZN6Father9FatherKeyEv
+// LLVM-SAME: ]
+// LLVM-SAME: }
+
+// OGCG: @_ZTV5Child = unnamed_addr constant { [4 x ptr], [3 x ptr] } {
+// OGCG-SAME: [4 x ptr] [
+// OGCG-SAME: ptr null,
+// OGCG-SAME: ptr null,
+// OGCG-SAME: ptr @_ZN5Child9MotherKeyEv,
+// OGCG-SAME: ptr @_ZN6Mother12MotherNonKeyEv
+// OGCG-SAME: ],
+// OGCG-SAME: [3 x ptr] [
+// OGCG-SAME: ptr inttoptr (i64 -8 to ptr),
+// OGCG-SAME: ptr null,
+// OGCG-SAME: ptr @_ZN6Father9FatherKeyEv
+// OGCG-SAME: ]
+// OGCG-SAME: }
+
// Mother vtable
// CIR: cir.global "private" external @_ZTV6Mother = #cir.vtable<{
@@ -91,46 +136,48 @@ void Child::MotherKey() {}
// OGCG-SAME: ]
// OGCG-SAME: }
-// Child vtable
-
-// CIR: cir.global "private" external @_ZTV5Child = #cir.vtable<{
-// CIR-SAME: #cir.const_array<[
-// CIR-SAME: #cir.ptr<null> : !cir.ptr<!u8i>,
-// CIR-SAME: #cir.ptr<null> : !cir.ptr<!u8i>,
-// CIR-SAME: #cir.global_view<@_ZN5Child9MotherKeyEv> : !cir.ptr<!u8i>,
-// CIR-SAME: #cir.global_view<@_ZN6Mother12MotherNonKeyEv> : !cir.ptr<!u8i>
-// CIR-SAME: ]> : !cir.array<!cir.ptr<!u8i> x 4>,
-// CIR-SAME: #cir.const_array<[
-// CIR-SAME: #cir.ptr<-8 : i64> : !cir.ptr<!u8i>,
-// CIR-SAME: #cir.ptr<null> : !cir.ptr<!u8i>,
-// CIR-SAME: #cir.global_view<@_ZN6Father9FatherKeyEv> : !cir.ptr<!u8i>
-// CIR-SAME: ]> : !cir.array<!cir.ptr<!u8i> x 3>
-// CIR-SAME: }> : [[CHILD_VTABLE_TYPE]]
-// LLVM: @_ZTV5Child = global { [4 x ptr], [3 x ptr] } {
-// LLVM-SAME: [4 x ptr] [
-// LLVM-SAME: ptr null,
-// LLVM-SAME: ptr null,
-// LLVM-SAME: ptr @_ZN5Child9MotherKeyEv,
-// LLVM-SAME: ptr @_ZN6Mother12MotherNonKeyEv
-// LLVM-SAME: ],
-// LLVM-SAME: [3 x ptr] [
-// LLVM-SAME: ptr inttoptr (i64 -8 to ptr),
-// LLVM-SAME: ptr null,
-// LLVM-SAME: ptr @_ZN6Father9FatherKeyEv
-// LLVM-SAME: ]
-// LLVM-SAME: }
-
-// OGCG: @_ZTV5Child = unnamed_addr constant { [4 x ptr], [3 x ptr] } {
-// OGCG-SAME: [4 x ptr] [
-// OGCG-SAME: ptr null,
-// OGCG-SAME: ptr null,
-// OGCG-SAME: ptr @_ZN5Child9MotherKeyEv,
-// OGCG-SAME: ptr @_ZN6Mother12MotherNonKeyEv
-// OGCG-SAME: ],
-// OGCG-SAME: [3 x ptr] [
-// OGCG-SAME: ptr inttoptr (i64 -8 to ptr),
-// OGCG-SAME: ptr null,
-// OGCG-SAME: ptr @_ZN6Father9FatherKeyEv
-// OGCG-SAME: ]
-// OGCG-SAME: }
+Child::Child() {}
+
+// CIR: cir.func {{.*}} @_ZN5ChildC2Ev(%[[THIS_ARG:.*]]: !cir.ptr<!rec_Child>
+// CIR: %[[THIS_ADDR:.*]] = cir.alloca {{.*}} ["this", init]
+// CIR: cir.store %[[THIS_ARG]], %[[THIS_ADDR]]
+// CIR: %[[THIS:.*]] = cir.load %[[THIS_ADDR]]
+// CIR: %[[MOTHER_BASE:.*]] = cir.base_class_addr %[[THIS]] : !cir.ptr<!rec_Child> nonnull [0] -> !cir.ptr<!rec_Mother>
+// CIR: cir.call @_ZN6MotherC2Ev(%[[MOTHER_BASE]]) nothrow : (!cir.ptr<!rec_Mother>) -> ()
+// CIR: %[[FATHER_BASE:.*]] = cir.base_class_addr %[[THIS]] : !cir.ptr<!rec_Child> nonnull [8] -> !cir.ptr<!rec_Father>
+// CIR: cir.call @_ZN6FatherC2Ev(%[[FATHER_BASE]]) nothrow : (!cir.ptr<!rec_Father>) -> ()
+// CIR: %[[CHILD_VPTR:.*]] = cir.vtable.address_point(@_ZTV5Child, address_point = <index = 0, offset = 2>) : !cir.vptr
+// CIR: %[[CHILD_VPTR_ADDR:.*]] = cir.vtable.get_vptr %[[THIS]] : !cir.ptr<!rec_Child> -> !cir.ptr<!cir.vptr>
+// CIR: cir.store{{.*}} %[[CHILD_VPTR]], %[[CHILD_VPTR_ADDR]] : !cir.vptr, !cir.ptr<!cir.vptr>
+// CIR: %[[FATHER_IN_CHILD_VPTR:.*]] = cir.vtable.address_point(@_ZTV5Child, address_point = <index = 1, offset = 2>) : !cir.vptr
+// CIR: %[[FATHER_BASE:.*]] = cir.base_class_addr %[[THIS]] : !cir.ptr<!rec_Child> nonnull [8] -> !cir.ptr<!rec_Father>
+// CIR: %[[FATHER_IN_CHILD_VPTR_ADDR:.*]] = cir.vtable.get_vptr %[[FATHER_BASE]] : !cir.ptr<!rec_Father> -> !cir.ptr<!cir.vptr>
+// CIR: cir.store{{.*}} %[[FATHER_IN_CHILD_VPTR]], %[[FATHER_IN_CHILD_VPTR_ADDR]] : !cir.vptr, !cir.ptr<!cir.vptr>
+// CIR: cir.return
+
+// The GEP instructions are different between LLVM and OGCG, but they calculate the same addresses.
+
+// LLVM: define{{.*}} void @_ZN5ChildC2Ev(ptr{{.*}} %[[THIS_ARG:.*]])
+// LLVM: %[[THIS_ADDR:.*]] = alloca ptr
+// LLVM: store ptr %[[THIS_ARG]], ptr %[[THIS_ADDR]]
+// LLVM: %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
+// LLVM: call void @_ZN6MotherC2Ev(ptr{{.*}} %[[THIS]])
+// LLVM: %[[FATHER_BASE:.*]] = getelementptr{{.*}} i8, ptr %[[THIS]], i32 8
+// LLVM: call void @_ZN6FatherC2Ev(ptr{{.*}} %[[FATHER_BASE]])
+// LLVM: store ptr getelementptr inbounds nuw (i8, ptr @_ZTV5Child, i64 16), ptr %[[THIS]]
+// LLVM: %[[FATHER_BASE:.*]] = getelementptr{{.*}} i8, ptr %[[THIS]], i32 8
+// LLVM: store ptr getelementptr inbounds nuw (i8, ptr @_ZTV5Child, i64 48), ptr %[[FATHER_BASE]]
+// LLVM: ret void
+
+// OGCG: define{{.*}} void @_ZN5ChildC2Ev(ptr{{.*}} %[[THIS_ARG:.*]])
+// OGCG: %[[THIS_ADDR:.*]] = alloca ptr
+// OGCG: store ptr %[[THIS_ARG]], ptr %[[THIS_ADDR]]
+// OGCG: %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
+// OGCG: call void @_ZN6MotherC2Ev(ptr {{.*}} %[[THIS]])
+// OGCG: %[[FATHER_BASE:.*]] = getelementptr{{.*}} i8, ptr %[[THIS]], i64 8
+// OGCG: call void @_ZN6FatherC2Ev(ptr{{.*}} %[[FATHER_BASE]])
+// OGCG: store ptr getelementptr inbounds inrange(-16, 16) ({ [4 x ptr], [3 x ptr] }, ptr @_ZTV5Child, i32 0, i32 0, i32 2), ptr %[[THIS]]
+// OGCG: %[[FATHER_BASE:.*]] = getelementptr{{.*}} i8, ptr %[[THIS]], i64 8
+// OGCG: store ptr getelementptr inbounds inrange(-16, 8) ({ [4 x ptr], [3 x ptr] }, ptr @_ZTV5Child, i32 0, i32 1, i32 2), ptr %[[FATHER_BASE]]
+// OGCG: ret void
|
AmrDeveloper
approved these changes
Aug 25, 2025
| assert(!nonVirtualOffset.isZero() || virtualOffset != nullptr); | ||
|
|
||
| // Compute the offset from the static and dynamic components. | ||
| mlir::Value baseOffset; |
There was a problem hiding this comment.
I think baseOffset is unused in this PR; the value is updated, but it is not used. Should it be removed from this PR?
| // Black-list all explicit and implicit references to 'this'. | ||
| // | ||
| // Do we need to worry about external references to 'this' derived | ||
| // from arbitrary code? If so, then anything which runs arbitrary |
There was a problem hiding this comment.
Suggested change
| // from arbitrary code? If so, then anything which runs arbitrary | |
| // from arbitrary code? If so, then anything which runs arbitrary |
bcardosolopes
approved these changes
Aug 25, 2025
This adds support for initializing the vptr members in a class that requires multiple vtables because of multiple inheritence. This still does not handle virtual bases.
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This adds support for initializing the vptr members in a class that requires multiple vtables because of multiple inheritence. This still does not handle virtual bases.