Re: Filed PR jit/66811: jit dumps aren't compilable as C (Re: A possible code generation issue)

[David Malcolm <dmalcolm@redhat.com>]

On Wed, 2015-07-08 at 10:15 -0400, David Malcolm wrote:
> On Mon, 2015-07-06 at 22:29 +0100, Dibyendu Majumdar wrote:
> > On 4 July 2015 at 23:09, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
> > > On 4 July 2015 at 22:41, David Malcolm <dmalcolm@redhat.com> wrote:
> > >>> 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.
> > >>
> > >>
> > >> Of course, it could well be a bug at my end.
> > >>
> > 
> > Dave,
> > 
> > Attached is a hacked version in C of the dump from the code. I thought
> > it might be useful to generate code directly using gcc -O3 -S on this
> > file - from what I can tell the generated code looks different from
> > what I am getting in libgccjit.
> > 
> > BTW the dump of types is problematic in many ways:
> > 1) types are in wrong order
> > 2) function types are incorrectly output
> > 3) array types are incorrectly output
> > 4) in one case as least a pointer was missing.
> > 
> > It would be useful if the generated dump was correct C so that it can
> > directly compiled in gcc.
> 
> Agreed.  I've filed this as an RFE for the jit as:
>   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66811

fixing typo in Subject: s/jumps/dumps/