Re: [Sbcl-commits] master: x86-64: don't combine arith + test.

And the test managed to deadlock on macos...

On Sat, Nov 29, 2025 at 1:17 AM Stas Boukarev <[email protected]> wrote:
>
> I made a test that tries a lot of different arithmetic combinations.
> But it takes hours to finish, even with multiple threads, I'm yet to
> see it through the end.
> And it still doesn't include all the combinations I want to test. Too
> bad I don't have thousands of cores.
>
> On Sat, Nov 29, 2025 at 1:14 AM Christophe Rhodes via Sbcl-devel
> <[email protected]> wrote:
> >
> > Thanks for these fixes.  Did you find them from miscompiled examples or
> > from Thinking Very Hard?
> >
> > Christophe
> >
> > stassats via Sbcl-commits <[email protected]> writes:
> >
> > > The branch "master" has been updated in SBCL:
> > >        via  6d2ffcff0b344fd9e2f25def3bede4e55e879cdd (commit)
> > >       from  6d747e69701c9b57e866bcf0ad94f492260f1ecc (commit)
> > >
> > > - Log -----------------------------------------------------------------
> > > commit 6d2ffcff0b344fd9e2f25def3bede4e55e879cdd
> > > Author: Stas Boukarev <[email protected]>
> > > Date:   Sat Nov 29 00:03:29 2025 +0300
> > >
> > >     x86-64: don't combine arith + test.
> > >
> > >     It actually doesn't work because there can be multiple flag-reading
> > >     instructions.
> > > ---
> > >  src/compiler/x86-64/insts.lisp | 13 ++++++-------
> > >  1 file changed, 6 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/src/compiler/x86-64/insts.lisp b/src/compiler/x86-64/insts.lisp
> > > index 4ee94720e..de73bf97b 100644
> > > --- a/src/compiler/x86-64/insts.lisp
> > > +++ b/src/compiler/x86-64/insts.lisp
> > > @@ -3574,6 +3574,7 @@
> > >  ;;; Per the processor manual, TEST clears OF and CF, so presumably
> > >  ;;; there is not a branch-if on either of those flags.
> > >  ;;; It shouldn't be a problem that removal of TEST leaves more flags affected.
> > > +#+nil ;; it doesn't account for multiple flag-reading instructions
> > >  (defpattern "ALU + test" ((add adc sub sbb and or xor neg sar shl shr) (test)) (stmt next)
> > >    (binding* (((size1 dst1 src1) (parse-2-operands stmt))
> > >               ((size2 dst2 src2) (parse-2-operands next))
> > > @@ -3614,16 +3615,14 @@
> > >                          :nl :nle :ng :nge)
> > >                         (and (eq size2 size1)
> > >                              ;; Assume there's no overflow for signed arithmetic
> > > -                            ;; Excluding
> > > -                            ;; sb-vm::fast--/fixnum=>fixnum
> > > -                            ;; sb-vm::fast--/signed=>signed
> > > -                            ;; sb-vm::fast---c/fixnum=>fixnum
> > > -                            ;; sb-vm::fast---c/signed=>signed
> > > -                            ;; because subtracting two negative numbers will set OF.
> > >                              (memq (vop-name (sb-assem::stmt-vop stmt))
> > > -                                  '(sb-vm::fast-+/fixnum=>fixnum
> > > +                                  '(sb-vm::fast--/fixnum=>fixnum
> > > +                                    sb-vm::fast-+/fixnum=>fixnum
> > > +                                    sb-vm::fast--/signed=>signed
> > >                                      sb-vm::fast-+/signed=>signed
> > > +                                    sb-vm::fast---c/fixnum=>fixnum
> > >                                      sb-vm::fast-+-c/fixnum=>fixnum
> > > +                                    sb-vm::fast---c/signed=>signed
> > >                                      sb-vm::fast-+-c/signed=>signed
> > >                                      sb-vm::fast-negate/fixnum
> > >                                      sb-vm::fast-negate/signed))))))))
> > >
> > > -----------------------------------------------------------------------
> > >
> > >
> > > hooks/post-receive
> >
> >
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