Pip Cet <pip...@gmail.com> writes: >> Pip Cet via Gcc-patches <gcc-patches@gcc.gnu.org> writes: >> > I'm working on the AVR cc0 -> CCmode conversion (bug#92729). One >> > problem is that the cmpelim pass is currently very strict in requiring >> > insns of the form >> > >> > (parallel [(set (reg:SI) (op:SI ... ...)) >> > (clobber (reg:CC REG_CC))]) >> > >> > when in fact AVR's insns often have the form >> > >> > (parallel [(set (reg:SI) (op:SI ... ...)) >> > (clobber (scratch:QI)) >> > (clobber (reg:CC REG_CC))]) >> > >> > The attached patch relaxes checks in the cmpelim code to recognize >> > such insns, and makes it attempt to recognize >> > >> > (parallel [(set (reg:CC REG_CC) (compare:CC ... ...)) >> > (set (reg:SI (op:SI ... ...))) >> > (clobber (scratch:QI))]) >> > >> > as a new insn for that example. This appears to work. >> >> The idea looks good. However, I think it'd be better (or at least >> more usual) for the define_insns to list the clobbers the other >> way around: >> >> (parallel [(set (reg:SI) (op:SI ... ...)) >> (clobber (reg:CC REG_CC)) >> (clobber (scratch:QI))]) > > That makes sense, thanks for the suggestion. I realized quite quickly > that I would have to reproduce the patterns precisely, including order > in a parallel, and decided to go with the wrong consistent option by > always placing the CC clobber last. > > My question is whether it makes more sense to recognize either form > (i.e. a clobber of targetm.flags_regnum at any position in a parallel) > or whether it's okay to assume that the clobber is always the second > element in the parallel. I'm leaning towards the latter version.
Yeah, I agree the latter sounds best. We should be able to test whether the rest of the parallel is suitable by adding a single_set test (after testing everything else). Thanks, Richard
