On Tue, Oct 17, 2017 at 2:18 PM, Matt Turner <matts...@gmail.com> wrote:
> On 10/12, Jason Ekstrand wrote: > >> For some reason, the any/all predicates don't work properly with SIMD32. >> In particular, it appears that a SEL with a QtrCtrl of 2H doesn't read >> the correct subset of the flag register and you end up getting garbage >> in the second half. Work around this by using a pair of 1-wide MOVs and >> scattering the result. This fixes the any/all instructions for SIMD32. >> > > Huh. I can see a lot of potential for hardware misbehavior here... > > Making things 1-wide makes a lot of sense, regardless of the bug you're > seeing. I'm in favor of that change. > > I picked a SEL instead of a predicated MOV instruction since the latter > is considered by our optimizer to be a partial write, and as such isn't > subject to CSE, etc. The difference is probably trivial, but I'd rather > just commit a patch to change things to be 1-wide, not s/SEL/MOV/, and > drop the added comments from the code. > I'm pretty sure a 1-wide SEL is also going to be considered a partial write.
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