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, 7 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 2d2cce8..4903f09 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -926,6 +926,13 @@ public:
   // Return the function body address of the given function.
   llvm::Constant *GetFunctionStart(const ValueDecl *Decl);
 
+  // Return whether RTTI information should be emitted for this target.
+  bool shouldEmitRTTI(bool ForEH = false) {
+    return (ForEH || getLangOpts().RTTI) && !getLangOpts().CUDAIsDevice &&
+           !(getLangOpts().OpenMP && getLangOpts().OpenMPIsTargetDevice &&
+             getTriple().isNVPTX());
+  }
+
   /// Get the address of the RTTI descriptor for the given type.
   llvm::Constant *GetAddrOfRTTIDescriptor(QualType Ty, bool ForEH = false);