[PATCH] D70157: Align branches within 32-Byte boundary

[Philip Reames via Phabricator via cfe-commits]

reames added a comment.

I want to chime in support of jyknight's meta comments - particularly the one about the need to balance execution speed vs code size differently in hot vs cold code.  For our use case, we have a very large amount of branch dense known cold paths, and being able to only align fast path branches would be a substantial space savings.

I also see value in having the prefix padding feature factored out generically.  If that mechanism is truly measurably faster than multi-byte nops - which if I reading comments correctly, has been claimed but not documented or measured? - using it generically for other alignment purposes would likely be worthwhile.

I'd also like to see - probably in a separate patch - support for auto-detecting whether the host CPU needs this mitigation.  Both -mcpu=native and various JITs will end up needing this, having the code centralized in one place would be good.


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  https://reviews.llvm.org/D70157/new/

https://reviews.llvm.org/D70157