On Wed, Aug 18, 2021 at 3:54 AM Jojo R <rjie...@linux.alibaba.com> wrote: > > > — Jojo > 在 2021年8月16日 +0800 PM3:15，Richard Biener <richard.guent...@gmail.com>，写道： > > On Fri, Aug 13, 2021 at 3:59 AM Jojo R <rjie...@linux.alibaba.com> wrote: > > > > — Jojo > 在 2021年8月11日 +0800 PM6:44，Richard Biener <richard.guent...@gmail.com>，写道： > > On Wed, Aug 11, 2021 at 11:28 AM Richard Sandiford > <richard.sandif...@arm.com> wrote: > > > Richard Biener <richard.guent...@gmail.com> writes: > > On Tue, Aug 10, 2021 at 10:33 AM Jojo R via Gcc-patches > <gcc-patches@gcc.gnu.org> wrote: > > > Some target like RISC-V allow to group vector register as a whole, > and only operate part of it in fact, but the 'init-regs' pass will add > initialization > for uninitialized registers. Add this hook to reject this action for reducing > instruction. > > > Are these groups "visible"? That is, are the pseudos multi-reg > pseudos? I wonder > if there's a more generic way to tame down initregs w/o introducing a new > target > hook. > > Btw, initregs is a red herring - it ideally should go away. See PR61810. > > So instead of adding to it can you see whether disabling the pass for RISC-V > works w/o fallout (and add a comment to the PR)? Maybe some more RTL > literate (in particular DF literate) can look at the remaining issue. > Richard, did you > ever have a look into the "issue" that initregs covers up (whatever > that exactly is)? > > > No, sorry. I don't really understand what it would be from the comment > in the code: > > [...] papers over some problems on the arm and other > processors where certain isa constraints cannot be handled by gcc. > These are of the form where two operands to an insn my not be the > same. The ra will only make them the same if they do not > interfere, and this can only happen if one is not initialized. > > That would definitely be an RA bug if true, since the constraints need > to be applied independently of dataflow information. But the comment > and code predate LRA and maybe no-one fancied poking around in reload > (hard to believe). > > I'd be very surprised if LRA gets this wrong. > > > OK, we're wondering since quite some time - how about changing the > gate of initregs to optimize > 0 && !targetm.lra_p ()? We'll hopefully > figure out the "real" issue the pass is papering over. At the same time > we're leaving old reload (and likely unmaintianed) targets unaffected. > > Richard, > > So this patch is not necessary ? > > I need to disable this pass in my situation only ? > I am afraid some side effect in my projects without this init-regs pass … ... > > > Can you try disabling the pass on RISC-V? > > Okay, I will do the test on GCC version 10.2, is it ok ? > It will take a few days :) > > Or which version do you suggest to do this ?
Well, as recent as possible - I would at least suggest 11.2, but trunk would be best of course. Richard. > Richard. > > Richard. > > Thanks, > Richard
