[MS ABI] Correctly make paths through covariant virtual bases
There can be multiple virtual bases which are on the path to a vfptr
when one vbase virtually inherits from another. We should prefer the
most derived virtual base which covariantly overrides a method in the
vfptr class; if we do not lengthen the path this way, we will end up
with too few vftable entries.
This fixes PR21073.
llvm-svn: 236239
diff --git a/clang/lib/AST/VTableBuilder.cpp b/clang/lib/AST/VTableBuilder.cpp
index 089520d..e4ae6f8 100644
--- a/clang/lib/AST/VTableBuilder.cpp
+++ b/clang/lib/AST/VTableBuilder.cpp
@@ -3451,11 +3451,11 @@
/// struct B : virtual A { virtual void f(); };
/// struct C : virtual A, B { virtual void f(); };
/// The path to A's vftable in C should be 'C, B, A', not 'C, A'.
-static bool
-findPathForVPtr(ASTContext &Context, const ASTRecordLayout &MostDerivedLayout,
- const CXXRecordDecl *RD, CharUnits Offset,
- llvm::SmallPtrSetImpl<const CXXRecordDecl *> &VBasesSeen,
- VPtrInfo::BasePath &FullPath, VPtrInfo *Info) {
+static bool findPathForVPtr(ASTContext &Context,
+ const ASTRecordLayout &MostDerivedLayout,
+ const CXXRecordDecl *RD, CharUnits Offset,
+ FinalOverriders &Overriders,
+ VPtrInfo::BasePath &FullPath, VPtrInfo *Info) {
if (RD == Info->BaseWithVPtr && Offset == Info->FullOffsetInMDC) {
Info->PathToBaseWithVPtr = FullPath;
return true;
@@ -3463,28 +3463,98 @@
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
- // Sort direct bases into non-virtual bases followed by virtual bases. This
- // approximates layout order with the exception of classes that do not contain
- // vptrs, and those don't affect our results.
- SmallVector<CXXBaseSpecifier, 4> Bases(RD->bases_begin(), RD->bases_end());
- std::stable_partition(Bases.begin(), Bases.end(),
- [](CXXBaseSpecifier bs) { return !bs.isVirtual(); });
-
- for (const auto &B : Bases) {
- const CXXRecordDecl *Base = B.getType()->getAsCXXRecordDecl();
- CharUnits NewOffset;
- if (!B.isVirtual())
- NewOffset = Offset + Layout.getBaseClassOffset(Base);
- else {
- if (!VBasesSeen.insert(Base).second)
- continue;
- NewOffset = MostDerivedLayout.getVBaseClassOffset(Base);
- }
+ auto Recurse = [&](const CXXRecordDecl *Base, CharUnits NewOffset) {
FullPath.push_back(Base);
- if (findPathForVPtr(Context, MostDerivedLayout, Base, NewOffset, VBasesSeen,
+ if (findPathForVPtr(Context, MostDerivedLayout, Base, NewOffset, Overriders,
FullPath, Info))
return true;
+ // Adding 'Base' didn't get us to the BaseWithVPtr, pop it off the stack so
+ // that we can try another.
FullPath.pop_back();
+ return false;
+ };
+
+ // Start with the non-virtual bases so that we correctly create paths to
+ // virtual bases *through* non-virtual bases.
+ for (const auto &B : RD->bases()) {
+ if (B.isVirtual())
+ continue;
+ const CXXRecordDecl *Base = B.getType()->getAsCXXRecordDecl();
+ CharUnits NewOffset = Offset + Layout.getBaseClassOffset(Base);
+ if (Recurse(Base, NewOffset))
+ return true;
+ }
+ // None of non-virtual bases got us to the BaseWithVPtr, we need to try the
+ // virtual bases.
+ std::set<std::pair<const CXXRecordDecl *, CharUnits>> VBases;
+ for (const auto &B : RD->bases()) {
+ if (!B.isVirtual())
+ continue;
+ const CXXRecordDecl *Base = B.getType()->getAsCXXRecordDecl();
+ CharUnits NewOffset = MostDerivedLayout.getVBaseClassOffset(Base);
+ VBases.insert(std::make_pair(Base, NewOffset));
+ }
+ // No virtual bases, bail out early.
+ if (VBases.empty())
+ return false;
+
+ CXXBasePaths Paths(/*FindAmbiguities=*/false, /*RecordPaths=*/false,
+ /*DetectVirtual=*/true);
+ // All virtual bases which are on the path to the BaseWithVPtr are not equal.
+ // Specifically, virtual paths which introduce additional covariant thunks
+ // must be preferred over paths which do not introduce such thunks.
+ for (const auto *MD : Info->BaseWithVPtr->methods()) {
+ if (!MD->isVirtual())
+ continue;
+ MD = MD->getCanonicalDecl();
+ // Let's find overriders for the BaseWithVPtr where the method is overriden
+ // with a covariant method.
+ FinalOverriders::OverriderInfo Overrider =
+ Overriders.getOverrider(MD, Info->FullOffsetInMDC);
+ BaseOffset BO =
+ ComputeReturnAdjustmentBaseOffset(Context, Overrider.Method, MD);
+ // Skip any overriders which are not return adjusting.
+ if (BO.isEmpty() || !BO.VirtualBase)
+ continue;
+
+ // Ok, let's iterate through our virtual bases looking for a base which
+ // provides a return adjusting overrider for this method.
+ const CXXRecordDecl *Base = nullptr;
+ CharUnits NewOffset;
+ for (auto VBasePair : VBases) {
+ const CXXRecordDecl *VBase = VBasePair.first;
+ // There might be a vbase which derives from a vbase which provides a
+ // covariant override for the method *and* provides its own covariant
+ // override.
+ // Because of this, we want to keep climbing up the inheritance lattice
+ // looking for the most derived virtual base which provides a covariant
+ // override for the method.
+ Paths.clear();
+ if (!VBase->isDerivedFrom(Base ? Base : Info->BaseWithVPtr, Paths) ||
+ !Paths.getDetectedVirtual())
+ continue;
+ const CXXMethodDecl *VBaseMD = MD->getCorrespondingMethodInClass(VBase);
+ CharUnits VBaseNewOffset = VBasePair.second;
+ Overrider = Overriders.getOverrider(VBaseMD, VBaseNewOffset);
+ BO = ComputeReturnAdjustmentBaseOffset(Context, Overrider.Method, MD);
+ // Skip any overriders which are not return adjusting.
+ if (BO.isEmpty() || !BO.VirtualBase)
+ continue;
+ Base = VBase;
+ NewOffset = VBaseNewOffset;
+ }
+
+ if (Base && Recurse(Base, NewOffset))
+ return true;
+ }
+ // There are no virtual bases listed as a base specifier which provides a
+ // covariant override. However, we may still need to go through the virtual
+ // base to get to BaseWithVPtr.
+ for (const auto &B : VBases) {
+ const CXXRecordDecl *Base = B.first;
+ CharUnits NewOffset = B.second;
+ if (Recurse(Base, NewOffset))
+ return true;
}
return false;
}
@@ -3492,13 +3562,13 @@
static void computeFullPathsForVFTables(ASTContext &Context,
const CXXRecordDecl *RD,
VPtrInfoVector &Paths) {
- llvm::SmallPtrSet<const CXXRecordDecl*, 4> VBasesSeen;
const ASTRecordLayout &MostDerivedLayout = Context.getASTRecordLayout(RD);
VPtrInfo::BasePath FullPath;
+ FinalOverriders Overriders(RD, CharUnits(), RD);
+ Overriders.dump();
for (VPtrInfo *Info : Paths) {
findPathForVPtr(Context, MostDerivedLayout, RD, CharUnits::Zero(),
- VBasesSeen, FullPath, Info);
- VBasesSeen.clear();
+ Overriders, FullPath, Info);
FullPath.clear();
}
}