On Fri, Sep 11, 2020 at 4:18 PM Segher Boessenkool <seg...@kernel.crashing.org> wrote: > > On Fri, Sep 11, 2020 at 08:07:39AM +0200, Richard Biener wrote: > > On Thu, Sep 10, 2020 at 5:12 PM Segher Boessenkool > > <seg...@kernel.crashing.org> wrote: > > > On Thu, Sep 10, 2020 at 04:33:30PM +0200, Richard Biener wrote: > > > > On Thu, Sep 10, 2020 at 4:22 PM Aaron Sawdey <acsaw...@linux.ibm.com> > > > > wrote: > > > > > If it feels like a hack, that would because it is a hack. > > > > > > > > > > What I’d really like to discuss is how to accomplish the real goal: > > > > > keep anything from trying to do other operations (zero/sign extend > > > > > for one) to POImode. > > > > > > > > > > Is there an existing mechanism for this? > > > > > > > > Not that I know, but somehow x86 gets away with OImode and XImode > > > > without > > > > providing too many patterns for those. > > > > > > What we were seeing is DSE (of all things!) tries to extract a DImode > > > from a POImode (and expects that insn to exist!) That is no good. > > > > Maybe. I don't know what kind of operations have to exist if a mode > > is present and what not. > > But are you sure this will be the only case you'll run into? > > No, I am not sure if there are bugs related to this elsewhere in the > compiler :-) > > Until 2014 (and documented just days ago ;-) ) all bits of a partial > integer mode were considered unknown.
All bits or all bits outside of its precision? I hope the latter ;) > I have looked at a lot of it in > our code the past weeks, and we still treat it like that in most places. > > We now see bootstrap problems if we use POImode in some contexts (that's > this PR96791). POImode can only live in pairs of VSX registers; taking > a subreg of POImode that would not be valid on one VSX register is not > okay. I guess the same applies to i?86 DImode living in two gpr regs. Or any multi-reg pseudo. It certainly shouldn't be dependent on whether we're dealing with a partial integer mode or not. > Maybe we are missing some hooks or macros? So this problem must be "solved" in some way already. How do we asses subreg validity? Through recog in the end? Richard. > > > Segher
