Optimize emission of `dynamic_cast` to final classes.

- When the destination is a final class type that does not derive from
  the source type, the cast always fails and is now emitted as a null
  pointer or call to __cxa_bad_cast.

- When the destination is a final class type that does derive from the
  source type, emit a direct comparison against the corresponding base
  class vptr value(s). There may be more than one such value in the case
  of multiple inheritance; check them all.

For now, this is supported only for the Itanium ABI. I expect the same thing is
possible for the MS ABI too, but I don't know what guarantees are made about
vfptr uniqueness.

Reviewed By: rjmccall

Differential Revision: https://reviews.llvm.org/D154658

1 files changed, 1 insertions, 3 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index ef49349..bb5d180 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -7152,9 +7152,7 @@ llvm::Constant *CodeGenModule::GetAddrOfRTTIDescriptor(QualType Ty,
   // Return a bogus pointer if RTTI is disabled, unless it's for EH.
   // FIXME: should we even be calling this method if RTTI is disabled
   // and it's not for EH?
-  if ((!ForEH && !getLangOpts().RTTI) || getLangOpts().CUDAIsDevice ||
-      (getLangOpts().OpenMP && getLangOpts().OpenMPIsTargetDevice &&
-       getTriple().isNVPTX()))
+  if (!shouldEmitRTTI(ForEH))
     return llvm::Constant::getNullValue(GlobalsInt8PtrTy);
 
   if (ForEH && Ty->isObjCObjectPointerType() &&