[PATCH] D31509: [InstCombine] Combine vector shuffles if the same operand can be reused

[Keno Fischer via Phabricator via llvm-commits]

loladiro added a comment.

I wasn't suggesting we blindly trust the user on shuffles, but that we somehow distinguish between masks generated by some earlier LLVM pass and masks passed in by the user. For the former I feel like it would make a lot of sense to be more aggressive about folding them than we are now, which for the latter the user may have used some target specific knowledge, so we may want to be less aggressive. I'm also fine with a TTI hook, happy to write the code. Somebody has to make a call here, and I don't think I'm the best person to do so - I just want all those redundant shuffles out of my code ;).


https://reviews.llvm.org/D31509