On 1/7/19 3:51 PM, Jakub Jelinek wrote: > Hi! > > As mentioned in that PR, we have a SI->DImode zero extension and RA happens > to choose to zero extend from a SImode memory slot which is the low part of > the DImode memory slot into which the zero extension is to be stored. > Unfortunately, the RTL DSE part really doesn't have infrastructure to > remember and, if needed, invalidate loads, it just remembers stores, so > handling this generically is quite unlikely at least for GCC9. > > This patch just handles that through a peephole2 (other option would be to > handle it in the define_split for the zero extension, but the peephole2 is > likely to catch more things). > > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? > > 2019-01-07 Jakub Jelinek <ja...@redhat.com> > > PR rtl-optimization/79593 > * config/i386/i386.md (reg = mem; mem = reg): New define_peephole2. Note I'd hacked up a POC in DSE and it caught something like 10 instances across a bootstrap. In the end I don't think this matters much in practice (peephole vs optimizing at the split point).
Jeff
