[PATCH] D27684: [X86][SSE] Fix domains for VZEXT_LOAD type instructions

Simon Pilgrim via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Mon Dec 12 13:35:22 PST 2016

RKSimon added a comment.

In https://reviews.llvm.org/D27684#620266, @mkuper wrote:

> Is there actually a domain crossing penalty for these cases?
>  (Adding Dave & Zia as authoritative sources of truth :-) )

The penalties are minor (and non-existent on some latest architectures), but definitely present on pre-AVX targets. It does allow us to be consistent along an instruction chain which isn't a bad thing. By allowing domain switching we also encourage float domain instructions which often have shorter encodings.



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