Hi! On Fri, Aug 14, 2020 at 05:47:02PM +0000, Pip Cet wrote: > On Fri, Aug 14, 2020 at 4:24 PM Segher Boessenkool > <seg...@kernel.crashing.org> wrote: > > On Fri, Aug 14, 2020 at 04:46:59PM +0530, Senthil Kumar Selvaraj via Gcc > > wrote: > > > (define_insn "*mov<mode>_insn_noclobber_flags" > > > [(set (match_operand:ALL1 0 "nonimmediate_operand" "=r,d ,q,r") > > > (match_operand:ALL1 1 "nox_general_operand" "r,n Ynn,r,q")) > > > (clobber (const_int 0))] > > > > This is not correct, clobbers like that are not defined RTL, and are > > actually used internally (by combine at least), so this will confuse > > that. > > > > If you want to say some alternative does not clobber anything, just use > > the constraint "X" for that alternative. > > Just to clarify, such clobbers would still show up in RTL, right?
Yes, as (clobber (scratch:CC)) (or whatever the mode is). No register will be allocated to it. You can do a define_split splitting it into the form without clobber, if you want? (You can "split" to just one insn fine.) It's neatest when written as a define_insn_and_split. > Because some passes, such as cmpelim, do not currently appear to deal > very well with extra clobbers, so that might be a problem. Not sure if it would mind here... It is not a clobber of a reg. > What I'm currently doing is this: > > (define_split > [(set (match_operand 0 "nonimmediate_operand") > (match_operand 1 "nox_general_operand"))] > "reload_completed && mov_clobbers_cc (insn, operands)" > [(parallel [(set (match_dup 0) (match_dup 1)) > (clobber (reg:CC REG_CC))])]) > > which, if I understand correctly, introduces the parallel-clobber > expression only when necessary, at the same time as post-reload > splitters introduce REG_CC references. Is that correct? Yes. And this will work correctly if somehow you ensure that REG_CC isn't live anywhere you introduce such a clobber. Segher
