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Diffstat (limited to 'llvm/docs/LangRef.rst')
| -rw-r--r-- | llvm/docs/LangRef.rst | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index d18d4ebac90..1a6549a15d6 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -6964,10 +6964,20 @@ Semantics: When directly supported, this intrinsic will either return a call to the appropriate cache clearing system call (usually ``__clear_cache``) when the caches are not unified (ARM, Mips) or just remove the call -altogether when they are (ex. x86_64). - -Targets must implement it directly to have either behaviour, as the -default is to bail with "Not Implemented" message. +altogether when they are (ex. x86_64). Some targets can lower these +directly into special instructions, if they have it. + +The default behaviour is to emit a call to ``__clear_cache``, so in +case a target doesn't support it, the user gets a linker error rather +than a compiler internal error. It also provides a work around to +the user (implement an empty function called ``__clear_cache``) while +LLVM doesn't implement it in the target's back-end. + +Please note that the caller is responsible for ensuring the cache +is actually cleared. This is most important in targets that don't +need to flush the cache directly (ex. x86_64) and could potentially +still execute old instructions while the cache is not cleared. LLVM +will *not* insert nops or busy-wait sequences. Standard C Library Intrinsics ----------------------------- |
