> On Jun 21, 2016, at 5:34 PM, Segher Boessenkool <seg...@kernel.crashing.org> > wrote: > > On Tue, Jun 21, 2016 at 03:14:51PM -0500, Bill Schmidt wrote: >> I discovered recently that, with -mcpu=power9, an attempt to generate a >> vspltish instruction resulted instead in an xxspltib followed by a vupkhsb. >> This is semantically correct but the extra instruction is not optimal. I >> found that there was some logic in xxspltib_constant_p to do special casing >> for const_vector with small constants, but not for vec_duplicate with small >> constants. This patch duplicates that logic so we can generate the single >> instruction when possible. > > This part is okay. > >> When I did this, I ran into a problem with an existing test case. We end up >> matching the *vsx_splat_v4si_internal pattern instead of falling back to the >> altivec_vspltisw pattern. The constraints don't match for constant input. >> To avoid this, I added a pattern ahead of this one that will match for VMX >> output registers and produce the vspltisw as desired. This corrected the >> failing test and produces the expected code. > > Why does the predicate allow constant input, while the constraints do not?
I have no idea why it was built that way. The predicate seems to provide for all sorts of things, but this and the subsequent pattern both handle only a subset of the constraints implied by it. To be honest, I didn't feel competent to try to fix the existing patterns. Do you have any suggestions for what to do instead? Thanks! Bill > >> I've added a test case to demonstrate the code works properly now in the >> usual case. > > Thanks :-) > > > Segher >
