[PATCH] D135807: [WIP][RISCV][InsertVSETVLI] Allow promotion of TA to TU and MA to MU

[Philip Reames via Phabricator via llvm-commits]

reames abandoned this revision.
reames added a comment.

Chatted w/ Craig about this offline.  As pointed out in review comments, there are some cases where switching from agnostic to undisturbed can have significant runtime cost - mostly by preventing otherwise legal speculative reordering.  We could maybe refine this into a patch which only exploits the possible state conversion for cheap instructions, but that's a bunch of infrastructure we don't have right now.  At the moment, we don't have a strong motivation to push this.  In some quick glancing at vector code, we're down to a small handful of tu or mu cases, and some extra toggles probably aren't worth aggressively optimizing.  We'll revisit when we have motivating examples.


Repository:
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https://reviews.llvm.org/D135807