On Mon, Aug 5, 2019 at 12:12 PM Richard Sandiford <richard.sandif...@arm.com> wrote: > > Uros Bizjak <ubiz...@gmail.com> writes: > > On Mon, Aug 5, 2019 at 11:13 AM Richard Sandiford > > <richard.sandif...@arm.com> wrote: > >> > >> Uros Bizjak <ubiz...@gmail.com> writes: > >> > On Sat, Aug 3, 2019 at 7:26 PM Richard Biener <rguent...@suse.de> wrote: > >> >> > >> >> On Thu, 1 Aug 2019, Uros Bizjak wrote: > >> >> > >> >> > On Thu, Aug 1, 2019 at 11:28 AM Richard Biener <rguent...@suse.de> > >> >> > wrote: > >> >> > > >> >> >>>> So you unconditionally add a smaxdi3 pattern - indeed this looks > >> >> >>>> necessary even when going the STV route. The actual regression > >> >> >>>> for the testcase could also be solved by turing the smaxsi3 > >> >> >>>> back into a compare and jump rather than a conditional move > >> >> >>>> sequence. > >> >> >>>> So I wonder how you'd do that given that there's > >> >> >>>> pass_if_after_reload > >> >> >>>> after pass_split_after_reload and I'm not sure we can split > >> >> >>>> as late as pass_split_before_sched2 (there's also a split _after_ > >> >> >>>> sched2 on x86 it seems). > >> >> >>>> > >> >> >>>> So how would you go implement {s,u}{min,max}{si,di}3 for the > >> >> >>>> case STV doesn't end up doing any transform? > >> >> >>> > >> >> >>> If STV doesn't transform the insn, then a pre-reload splitter splits > >> >> >>> the insn back to compare+cmove. > >> >> >> > >> >> >> OK, that would work. But there's no way to force a jumpy sequence > >> >> >> then > >> >> >> which we know is faster than compare+cmove because later RTL > >> >> >> if-conversion passes happily re-discover the smax (or conditional > >> >> >> move) > >> >> >> sequence. > >> >> >> > >> >> >>> However, considering the SImode move > >> >> >>> from/to int/xmm register is relatively cheap, the cost function > >> >> >>> should > >> >> >>> be tuned so that STV always converts smaxsi3 pattern. > >> >> >> > >> >> >> Note that on both Zen and even more so bdverN the int/xmm transition > >> >> >> makes it no longer profitable but a _lot_ slower than the cmp/cmov > >> >> >> sequence... (for the loop in hmmer which is the only one I see > >> >> >> any effect of any of my patches). So identifying chains that > >> >> >> start/end in memory is important for cost reasons. > >> >> > > >> >> > Please note that the cost function also considers the cost of move > >> >> > from/to xmm. So, the cost of the whole chain would disable the > >> >> > transformation. > >> >> > > >> >> >> So I think the splitting has to happen after the last if-conversion > >> >> >> pass (and thus we may need to allocate a scratch register for this > >> >> >> purpose?) > >> >> > > >> >> > I really hope that the underlying issue will be solved by a machine > >> >> > dependant pass inserted somewhere after the pre-reload split. This > >> >> > way, we can split unconverted smax to the cmove, and this later pass > >> >> > would handle jcc and cmove instructions. Until then... yes your > >> >> > proposed approach is one of the ways to avoid unwanted if-conversion, > >> >> > although sometimes we would like to split to cmove instead. > >> >> > >> >> So the following makes STV also consider SImode chains, re-using the > >> >> DImode chain code. I've kept a simple incomplete smaxsi3 pattern > >> >> and also did not alter the {SI,DI}mode chain cost function - it's > >> >> quite off for TARGET_64BIT. With this I get the expected conversion > >> >> for the testcase derived from hmmer. > >> >> > >> >> No further testing sofar. > >> >> > >> >> Is it OK to re-use the DImode chain code this way? I'll clean things > >> >> up some more of course. > >> > > >> > Yes, the approach looks OK to me. It makes chain building mode > >> > agnostic, and the chain building can be used for > >> > a) DImode x86_32 (as is now), but maybe 64bit minmax operation can be > >> > added. > >> > b) SImode x86_32 and x86_64 (this will be mainly used for SImode > >> > minmax and surrounding SImode operations) > >> > c) DImode x86_64 (also, mainly used for DImode minmax and surrounding > >> > DImode operations) > >> > > >> >> Still need help with the actual patterns for minmax and how the > >> >> splitters > >> >> should look like. > >> > > >> > Please look at the attached patch. Maybe we can add memory_operand as > >> > operand 1 and operand 2 predicate, but let's keep things simple for > >> > now. > >> > > >> > Uros. > >> > > >> > Index: i386.md > >> > =================================================================== > >> > --- i386.md (revision 274008) > >> > +++ i386.md (working copy) > >> > @@ -17721,6 +17721,27 @@ > >> > std::swap (operands[4], operands[5]); > >> > }) > >> > > >> > +;; min/max patterns > >> > + > >> > +(define_code_attr smaxmin_rel [(smax "ge") (smin "le")]) > >> > + > >> > +(define_insn_and_split "<code><mode>3" > >> > + [(set (match_operand:SWI48 0 "register_operand") > >> > + (smaxmin:SWI48 (match_operand:SWI48 1 "register_operand") > >> > + (match_operand:SWI48 2 "register_operand"))) > >> > + (clobber (reg:CC FLAGS_REG))] > >> > + "TARGET_STV && TARGET_SSE4_1 > >> > + && can_create_pseudo_p ()" > >> > + "#" > >> > + "&& 1" > >> > + [(set (reg:CCGC FLAGS_REG) > >> > + (compare:CCGC (match_dup 1)(match_dup 2))) > >> > + (set (match_dup 0) > >> > + (if_then_else:SWI48 > >> > + (<smaxmin_rel> (reg:CCGC FLAGS_REG)(const_int 0)) > >> > + (match_dup 1) > >> > + (match_dup 2)))]) > >> > + > >> > >> The pattern could in theory be matched after the last pre-RA split pass > >> has run, so I think the pattern still needs to have constraints and be > >> matchable even without can_create_pseudo_p. It looks like the split > >> above should work post-RA. > >> > >> A bit pedantic, because the pattern's probably fine in practice... > > > > Currently, all unmatched STV patterns split before reload, and there > > were no problems. If the pattern matches after last pre-RA split, then > > the post-reload splitter will fail, since can_create_pseudo_p also > > applies to the part that splits the insn. > > But what I meant was: you should be able to remove the > can_create_pseudo_p () and add constraints. (You'd have to remove > can_create_pseudo_p () with constraints anyway, since the insn > wouldn't match after RA otherwise.)
I was under impression that it is better to split pseudo->pseudo, so reload has some more freedom on what register to choose, especially with matched and earlyclobbered DImode regs in x86_32 DImode patterns. There were some complications with andn pattern (that needed earlyclobber on a register to avoid clobbering registers in a memory address), and it was necessary to clobber the whole DImode register pair, wasting a SImode register. We can avoid all these complications by splitting before the RA, where also a pseudo can be allocated. Uros.