Kristian Høgsberg <k...@bitplanet.net> writes: > On Thu, Oct 22, 2015 at 12:24 PM, Matt Turner <matts...@gmail.com> wrote: >> On Thu, Oct 22, 2015 at 11:37 AM, Kristian Høgsberg Kristensen >> <k...@bitplanet.net> wrote: >>> The scalar destination registers break copy propagation. Instead compute >>> the results to a regular register and then reference a component when we >>> later use the result as a source. >> >> It might be hairy to get it working, but making copy propagation >> handle scalar destinations is the "right" way forward. >>
I'm pretty sure use-def chains will help with that :). >> If we commit this patch, and later implement support for copy >> propagating with scalar destinations, how will we remember to change >> this back? > > What's the harm in leaving it in? > Scalar instructions take less cycles to execute and consume less registers than vector ones -- The latter isn't a huge deal right now because the register allocator will expand it to a 32B register anyway, so the most you save currently is one register in SIMD16 mode. Let's put an XXX comment so we remember to change this back to a scalar when the remaining compiler infrastructure is fixed to handle them properly. With that change this patch is: Reviewed-by: Francisco Jerez <curroje...@riseup.net> > Kristian
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