Weird problem

[David Malcolm]

On Mon, 2015-06-29 at 21:11 -0400, David Malcolm wrote:
> On Mon, 2015-06-29 at 22:25 +0100, Dibyendu Majumdar wrote:
> > On 29 June 2015 at 22:08, David Malcolm <dmalcolm@redhat.com> wrote:
> > 
> > > Looking at src/lvm.c, I see that the signature of luaV_tonumber and that
> > > lua_Number can be various types, including "double".
> > >   int luaV_tonumber_ (const TValue *obj, lua_Number *n)
> > >
> > 
> > I am using double as lua_Number.
> > 
> > > Does the type signature of luaV_tonumber as compiled by the main
> > > compiler agree with that supplied by gcc_jit_context_new_function?  If
> > > one of them is e.g. expecting a float *, but the other is expecting a
> > > double *, then you might get the symptoms you're seeing.
> > >
> > 
> > I checked this - I think they match.
> > 
> > > If that doesn't highlight a cause, maybe you're running into a libgccjit
> > > bug.  If so, can you generate a reproducer and post it here so I can
> > > poke at it please?
> > >
> > 
> > Attached is a reproducer.
> 
> Thanks; I'm able to run the reproducer, at least to the point of being
> able to invoke gcc_jit_context_compile on it.
> 
> Interestingly, looking at the gimple dump (via
> GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE), I see:
> 
>   <float:64> OP_RAVI_TOFLT_n_2_8.0;
>   <float:64> OP_RAVI_TOFLT_n_2_8.1;
>   [...snip...]
>   <float:64> OP_RAVI_TOFLT_n_2_8;
>   [...snip...]
> 
> OP_RAVI_TOFLT_if_not_float_2_10:
>   OP_RAVI_TOFLT_n_2_8.0 = OP_RAVI_TOFLT_n_2_8;
>   printf ("number %p = %f before call to luaV_number",
> &OP_RAVI_TOFLT_n_2_8.0, OP_RAVI_TOFLT_n_2_8);
>   OP_RAVI_TOFLT_n_2_8.1 = OP_RAVI_TOFLT_n_2_8;
>   [...snip...]
>   OP_RAVI_TOFLT_n_2_8.1 = OP_RAVI_TOFLT_n_2_8;
>   D.392 = 0;
>   D.393 = base + D.392;
>   D.405 = luaV_tonumber_ (D.393, &OP_RAVI_TOFLT_n_2_8.1);
>           ^^^^^^^^^^^^^^ here's the call          ^^^^^
>   comparison_0_12 = D.405 == 0;
>   if (comparison_0_12 != 0) goto
> OP_RAVI_TOFLT_if_conversion_failed_2_13; else goto
> OP_RAVI_TOFLT_if_conversion_ok_2_14;
> 
> OP_RAVI_TOFLT_done_2_11:
>   D.390 = L->ci;
>   base = D.390->u.l.base;
>   D.399 = 16;
>   D.400 = base + D.399;
>   L->top = D.400;
>   D.394 = cl->p;
>   D.406 = D.394->sizep;
>   comparison_0_15 = D.406 > 0;
>   if (comparison_0_15 != 0) goto OP_RETURN_if_sizep_gt_0_3_16; else goto
> OP_RETURN_else_sizep_gt_0_3_17;
> 
> OP_RAVI_TOFLT_if_conversion_failed_2_13:
>   luaG_runerror (L, "number expected");
>   goto OP_RAVI_TOFLT_if_conversion_ok_2_14;
>   OP_RAVI_TOFLT_if_conversion_ok_2_14:
>   printf ("number ok = %f", OP_RAVI_TOFLT_n_2_8);
> 
>   [...snip...]
> 
> which, if I'm reading it right, suggests that the local has effectively
> been split into three locals during the conversion to gimple, and that a
> ptr to
>   OP_RAVI_TOFLT_n_2_8.1
> is passed to luaV_tonumber_, but
>   OP_RAVI_TOFLT_n_2_8
> is then used.
> 
> This is feeling like a bug at my end; sorry.  I'll continue to
> investigate.

Definitely looks like a bug at my end.

I've created a minimal reproducer, and filed it as
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66700.

I plan to investigate further tomorrow.

Sorry about this.

Dave