[clang] [clang] Fix crash in dynamic_cast final class optimization (PR #152076)

[Eli Friedman via cfe-commits]

================
@@ -1722,41 +1728,95 @@ 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();
+  auto AuthenticateVTable = [&](Address ThisAddr, const CXXRecordDecl *Decl) {
+    if (!CGF.getLangOpts().PointerAuthCalls)
----------------
efriedma-quic wrote:

This PointerAuthCalls check is redundant?

https://github.com/llvm/llvm-project/pull/152076