From: David Malcolm <dmalcolm@redhat.com>
To: Dibyendu Majumdar <mobile@majumdar.org.uk>
Cc: jit@gcc.gnu.org
Subject: Re: A possible code generation issue
Date: Thu, 01 Jan 2015 00:00:00 -0000 [thread overview]
Message-ID: <1436046085.24803.35.camel@surprise> (raw)
In-Reply-To: <CACXZuxfb+OOW6Mc4GPBfUaE4VSAhOmy=f1KCXxLmXq=Mw7DdyQ@mail.gmail.com>
On Sat, 2015-07-04 at 16:58 +0100, Dibyendu Majumdar wrote:
> On 4 July 2015 at 14:20, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
> > On 4 July 2015 at 13:11, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
> >> Looks like in the failure case the code is being incorrectly
> >> optimized. I wonder if this is a manifestation of the get_address bug,
> >> perhaps the real fix will be better than the patch I am using. I will
> >> use the latest gcc 5 branch and see if that helps.
> >>
> >
> > Hi Dave,
> >
> > I am now using the latest gcc-5-branch from gcc github mirror.
> > Unfortunately the issue still persists.
> >
> > If set optimization level to 0 or 1, then it works ok, but at levels 2
> > or 3 the break occurs.
> >
>
> Adding the -fno-strict-aliasing appears to resolve the issue with -O2
> and -O3 but with this enabled the benchmarks are degraded.
If "-fno-strict-aliasing" resolved this, then that suggests that there
are various casts in the code that if this were C would take us into
"undefined behavior" territory, and the optimizer is trying a little too
hard. This isn't C, but similar rules apply. If that's what this is,
then this is at least a documentation issue with libgccjit; we need to
document what the rules are.
If this is the case it's normally possible to work around it in C by
rewriting casts using unions.
Of course, it could well be a bug at my end.
In any case, I'm not going to be able to have a proper look at this
until Monday (it's the July 4th holiday weekend here in the US); sorry.
Sorry about this
Dave
next prev parent reply other threads:[~2015-07-04 21:49 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-01 0:00 Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Filed PR jit/66812 for the " David Malcolm
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` [PATCH] PR jit/66812: Candidate fix for for the code generation issue, v1 David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Filed PR jit/66812 for the code generation issue Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm [this message]
2015-01-01 0:00 ` A possible " Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` PR jit/66783 (Re: A possible code generation issue) David Malcolm
2015-01-01 0:00 ` [PATCH, committed] PR jit/66783: prevent use of opaque structs David Malcolm
2015-01-01 0:00 ` Filed PR jit/66811: jit jumps aren't compilable as C (Re: A possible code generation issue) David Malcolm
2015-01-01 0:00 ` Filed PR jit/66811: jit dumps " David Malcolm
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