From: Jeff Law <law@redhat.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Richard Sandiford <richard.sandiford@arm.com>,
gcc-patches List <gcc-patches@gcc.gnu.org>
Subject: Re: [RFA] [PR rtl-optimization/90275] Handle nop reg->reg copies in cse
Date: Thu, 12 Mar 2020 12:47:04 -0600 [thread overview]
Message-ID: <6450d3fd3267fe014142323a147696503b336857.camel@redhat.com> (raw)
In-Reply-To: <20200312182357.GI22482@gate.crashing.org>
On Thu, 2020-03-12 at 13:23 -0500, Segher Boessenkool wrote:
>
> > > I don't know if this patch makes matters worse or not. It doesn't seem
> > > suitable for stage 4 though. And Richard said the cse.c part breaks
> > > rs6000, if that is true, yes I do object ;-)
> > The rs6000 port breakage is trivial to fix. In fact, I did so and ran it
> > through
> > my tester, which includes ppc64le and ppc64 a slew of *-elf targets x86
> > native
> > and more.
>
> I don't see anything rs6000 below? Is it just this generic code?
It's just generic code. THe rs6000 issue is fixed by the !CALL_P condition.
>
> > @@ -5324,9 +5324,11 @@ cse_insn (rtx_insn *insn)
> > }
> >
> > /* Similarly, lots of targets don't allow no-op
> > - (set (mem x) (mem x)) moves. */
> > + (set (mem x) (mem x)) moves. Even (set (reg x) (reg x))
> > + might be impossible for certain registers (like CC registers). */
> > else if (n_sets == 1
> > - && MEM_P (trial)
> > + && ! CALL_P (insn)
> > + && (MEM_P (trial) || REG_P (trial))
> > && MEM_P (dest)
> > && rtx_equal_p (trial, dest)
> > && !side_effects_p (dest)
>
> This adds the !CALL_P (no space btw) condition, why is that?
Because n_sets is not valid for CALL_P insns which resulted in a failure on ppc.
See find_sets_in_insn which ignores the set on the LHS of a call. So imagine if
we had a nop register set in parallel with a (set (reg) (call ...)). We'd end up
deleting the entire PARALLEL which is obviously wrong.
One could argue that find_sets_in_insn should be fixed as well. I'd be worried
about fallout from that.
jeff
next prev parent reply other threads:[~2020-03-12 18:47 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-05 1:04 Jeff Law
2020-02-05 6:26 ` Jakub Jelinek
2020-02-05 12:09 ` Segher Boessenkool
2020-02-05 13:31 ` Richard Sandiford
2020-02-06 13:01 ` Jeff Law
2020-02-06 13:57 ` Segher Boessenkool
2020-02-07 16:01 ` Jeff Law
2020-02-08 16:41 ` Segher Boessenkool
2020-03-12 18:03 ` Jeff Law
2020-03-12 18:23 ` Segher Boessenkool
2020-03-12 18:47 ` Jeff Law [this message]
2020-03-12 20:26 ` Segher Boessenkool
2020-03-12 20:56 ` Jeff Law
2020-03-13 10:29 ` Richard Sandiford
2020-03-12 22:11 ` Jeff Law
2020-03-13 8:09 ` Christophe Lyon
2020-03-13 21:49 ` Jeff Law
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