Filed PR jit/66812 for the code generation issue

[David Malcolm]

On Wed, 2015-07-08 at 22:54 +0100, Dibyendu Majumdar wrote:
> Apologies I think the previous description of the flow was incorrect.
> Here is my second attempt (this is doing my head in so I will stop
> now):

[snip detailed analysis of bytecode]

Thanks.

So it's basically:

  * do a bunch of stuff
  * then set R(1) to boolean false in that last LOADBOOL op
  * then return


> 12 [3] LOADBOOL 1 0 0
> 
>   (&L->ci->u.l.base[(int)1])->value_.b = (int)0;
>   (&L->ci->u.l.base[(int)1])->tt_ = (int)1;
> 
> Above sets the register 1 to false and this is the return value.

I've been poring over the dumps:
https://dmalcolm.fedorapeople.org/gcc/2015-07-08/libgccjit-bug_rdump/
and I believe the problem is in pass "fre1"; it's eliminating this
statement for some reason:
  (&L->ci->u.l.base[(int)1])->value_.b = (int)0;

so 
  R1.tt_ = 1 (correct)
but:
  R1.value_.i = K0.value_.i  (incorrect, is int 10, not 0)

The statement is still present at pass 034t.ealias:
https://dmalcolm.fedorapeople.org/gcc/2015-07-08/libgccjit-bug_rdump/fake.c.034t.ealias
 
but is optimized away in pass 035t.fre1:
https://dmalcolm.fedorapeople.org/gcc/2015-07-08/libgccjit-bug_rdump/fake.c.035t.fre1

I'll have a more detailed look tomorrow at why fre1 is getting it wrong.

[snip]