1 files changed, 54 insertions, 33 deletions

diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index aae1481..5ffc1ed 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -226,6 +226,10 @@ public:
     return hasUniqueVTablePointer(DestRecordTy);
   }
 
+  std::optional<ExactDynamicCastInfo>
+  getExactDynamicCastInfo(QualType SrcRecordTy, QualType DestTy,
+                          QualType DestRecordTy) override;
+
   llvm::Value *emitDynamicCastCall(CodeGenFunction &CGF, Address Value,
                                    QualType SrcRecordTy, QualType DestTy,
                                    QualType DestRecordTy,
@@ -234,6 +238,7 @@ public:
   llvm::Value *emitExactDynamicCast(CodeGenFunction &CGF, Address ThisAddr,
                                     QualType SrcRecordTy, QualType DestTy,
                                     QualType DestRecordTy,
+                                    const ExactDynamicCastInfo &CastInfo,
                                     llvm::BasicBlock *CastSuccess,
                                     llvm::BasicBlock *CastFail) override;
 
@@ -1681,10 +1686,11 @@ llvm::Value *ItaniumCXXABI::emitDynamicCastCall(
   return Value;
 }
 
-llvm::Value *ItaniumCXXABI::emitExactDynamicCast(
-    CodeGenFunction &CGF, Address ThisAddr, QualType SrcRecordTy,
-    QualType DestTy, QualType DestRecordTy, llvm::BasicBlock *CastSuccess,
-    llvm::BasicBlock *CastFail) {
+std::optional<CGCXXABI::ExactDynamicCastInfo>
+ItaniumCXXABI::getExactDynamicCastInfo(QualType SrcRecordTy, QualType DestTy,
+                                       QualType DestRecordTy) {
+  assert(shouldEmitExactDynamicCast(DestRecordTy));
+
   ASTContext &Context = getContext();
 
   // Find all the inheritance paths.
@@ -1722,41 +1728,56 @@ llvm::Value *ItaniumCXXABI::emitExactDynamicCast(
     if (!Offset)
       Offset = PathOffset;
     else if (Offset != PathOffset) {
-      // Base appears in at least two different places. Find the most-derived
-      // object and see if it's a DestDecl. Note that the most-derived object
-      // must be at least as aligned as this base class subobject, and must
-      // have a vptr at offset 0.
-      ThisAddr = Address(emitDynamicCastToVoid(CGF, ThisAddr, SrcRecordTy),
-                         CGF.VoidPtrTy, ThisAddr.getAlignment());
-      SrcDecl = DestDecl;
-      Offset = CharUnits::Zero();
-      break;
+      // Base appears in at least two different places.
+      return ExactDynamicCastInfo{/*RequiresCastToPrimaryBase=*/true,
+                                  CharUnits::Zero()};
     }
   }
+  if (!Offset)
+    return std::nullopt;
+  return ExactDynamicCastInfo{/*RequiresCastToPrimaryBase=*/false, *Offset};
+}
 
-  if (!Offset) {
-    // If there are no public inheritance paths, the cast always fails.
-    CGF.EmitBranch(CastFail);
-    return llvm::PoisonValue::get(CGF.VoidPtrTy);
-  }
+llvm::Value *ItaniumCXXABI::emitExactDynamicCast(
+    CodeGenFunction &CGF, Address ThisAddr, QualType SrcRecordTy,
+    QualType DestTy, QualType DestRecordTy,
+    const ExactDynamicCastInfo &ExactCastInfo, llvm::BasicBlock *CastSuccess,
+    llvm::BasicBlock *CastFail) {
+  const CXXRecordDecl *SrcDecl = SrcRecordTy->getAsCXXRecordDecl();
+  const CXXRecordDecl *DestDecl = DestRecordTy->getAsCXXRecordDecl();
+
+  llvm::Value *VTable = nullptr;
+  if (ExactCastInfo.RequiresCastToPrimaryBase) {
+    // Base appears in at least two different places. Find the most-derived
+    // object and see if it's a DestDecl. Note that the most-derived object
+    // must be at least as aligned as this base class subobject, and must
+    // have a vptr at offset 0.
+    llvm::Value *PrimaryBase =
+        emitDynamicCastToVoid(CGF, ThisAddr, SrcRecordTy);
+    ThisAddr = Address(PrimaryBase, CGF.VoidPtrTy, ThisAddr.getAlignment());
+    SrcDecl = DestDecl;
+    Address VTablePtrPtr = ThisAddr.withElementType(CGF.VoidPtrPtrTy);
+    VTable = CGF.Builder.CreateLoad(VTablePtrPtr, "vtable");
+  } else
+    VTable = CGF.GetVTablePtr(ThisAddr, CGF.UnqualPtrTy, SrcDecl);
 
   // Compare the vptr against the expected vptr for the destination type at
-  // this offset. Note that we do not know what type ThisAddr points to in
-  // the case where the derived class multiply inherits from the base class
-  // so we can't use GetVTablePtr, so we load the vptr directly instead.
-  llvm::Instruction *VPtr = CGF.Builder.CreateLoad(
-      ThisAddr.withElementType(CGF.VoidPtrPtrTy), "vtable");
-  CGM.DecorateInstructionWithTBAA(
-      VPtr, CGM.getTBAAVTablePtrAccessInfo(CGF.VoidPtrPtrTy));
-  llvm::Value *Success = CGF.Builder.CreateICmpEQ(
-      VPtr, getVTableAddressPoint(BaseSubobject(SrcDecl, *Offset), DestDecl));
-  llvm::Value *Result = ThisAddr.emitRawPointer(CGF);
-  if (!Offset->isZero())
-    Result = CGF.Builder.CreateInBoundsGEP(
-        CGF.CharTy, Result,
-        {llvm::ConstantInt::get(CGF.PtrDiffTy, -Offset->getQuantity())});
+  // this offset.
+  llvm::Constant *ExpectedVTable = getVTableAddressPoint(
+      BaseSubobject(SrcDecl, ExactCastInfo.Offset), DestDecl);
+  llvm::Value *Success = CGF.Builder.CreateICmpEQ(VTable, ExpectedVTable);
+  llvm::Value *AdjustedThisPtr = ThisAddr.emitRawPointer(CGF);
+
+  if (!ExactCastInfo.Offset.isZero()) {
+    CharUnits::QuantityType Offset = ExactCastInfo.Offset.getQuantity();
+    llvm::Constant *OffsetConstant =
+        llvm::ConstantInt::get(CGF.PtrDiffTy, -Offset);
+    AdjustedThisPtr = CGF.Builder.CreateInBoundsGEP(CGF.CharTy, AdjustedThisPtr,
+                                                    OffsetConstant);
+  }
+
   CGF.Builder.CreateCondBr(Success, CastSuccess, CastFail);
-  return Result;
+  return AdjustedThisPtr;
 }
 
 llvm::Value *ItaniumCXXABI::emitDynamicCastToVoid(CodeGenFunction &CGF,