[libcxx-commits] [PATCH] D115367: [NFC][libcxxabi] Pulled guard byte code out of GuardObject
Daniel McIntosh via Phabricator via libcxx-commits
libcxx-commits at lists.llvm.org
Mon Dec 13 09:48:37 PST 2021
DanielMcIntosh-IBM marked an inline comment as done.
DanielMcIntosh-IBM added inline comments.
================
Comment at: libcxxabi/src/cxa_guard_impl.h:15
*
* The first "guard byte" (which is checked by the compiler) is set only upon
* the completion of cxa release.
----------------
ldionne wrote:
> This is confusing me -- does the compiler really check the guard byte? Isn't it what we do in the library when we do `guard_byte.load(std::_AO_Acquire) != UNSET`?
Yes, for performance reasons we check it inline before calling `__cxa_guard_acquire`: https://godbolt.org/z/hY1555Wcx. I believe in clang this is generated around clang/lib/CodeGen/ItaniumCXXABI.cpp:2470. As you point out, we also check it inside `__cxa_guard_acquire`, I assume this is in case the library is used with a compiler that doesn't generate the inline check (or something along those lines).
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D115367/new/
https://reviews.llvm.org/D115367
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