[PATCH] D154658: Optimize emission of `dynamic_cast` to final classes.

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith created this revision.
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- 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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D154658

Files:
  clang/lib/AST/ExprCXX.cpp
  clang/lib/CodeGen/CGCXXABI.h
  clang/lib/CodeGen/CGExprCXX.cpp
  clang/lib/CodeGen/ItaniumCXXABI.cpp
  clang/lib/CodeGen/MicrosoftCXXABI.cpp
  clang/test/CodeGenCXX/dynamic-cast-always-null.cpp
  clang/test/CodeGenCXX/dynamic-cast-exact.cpp

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