Re: tree-ssa branch broken

[Daniel Berlin <dberlin at dberlin dot org>]

On Tue, 2 Jul 2002, Graham Stott wrote:

> Diego Novillo wrote:
> > On Sat, 29 Jun 2002, Graham Stott wrote:
> > 
> > 
> >>I get the same segv compiling crtstuff.c with the stage2 compiler just
> >>built by stage1 and that is with and without rtl checking enabled.
> >>
> > 
> > It's possible that I'm not getting a segv because of the older
> > binutils I'm running.  I still have not had time to look into it
> > any more than this.
> Interestingly I can get both the segv and rtl checking failure :-)
> 
> It depends very much on your stack layout which part of the stack
> gets trampled. The segv occurs when the recog () return address gets
> trampled and the rtl checking failure occurs when the INSN parameter
> to recog_memozied_1 () gets trampled.
> 
> I found this out when adding some debuging code to recog_memozied_1 ()
> resulted in the rtl checking failure rather than segv.
> 
> In both cases the trample occurs during the same call to recog () from
> recog_memoized_1 ().
> 
> I think it's a problem with SIMPLE but I'm having difficulty pinpointing
> exactly what although I do suspect SIMPLE is doing something wrong when
> processing the "operands[N] = x" assigments where operands is declared as
> 
> 		rtx * const operands = &recog_data.operand[0];

Ah, here's the bug.

Check this out:

We move the initializer to before the initialization of it's rhs.

Like so:

recog_2 (simplified):

  struct rtx_def * * const operands;
...
  struct recog_data * recog_data.4070;
 ...
  operands = (struct rtx_def * *)recog_data.4070;
....
    recog_data.4070 = &recog_data;
        recog_data.4071 = (struct rtx_def * *)recog_data.4070;


Wheee.
Evil.

It looks like we end up putting something in the wrong level, because it's 
really:
  int _code.2667;
  unsigned char T.2666;
  int _code.2665;
  union rtunion * retval.2664;
  operands = (struct rtx_def * *)recog_data.4070;
  struct rtx_def * x1;
  struct rtx_def * x2;
  struct rtx_def * x3;
  struct rtx_def * x4;
  struct rtx_def * x5;
  
(IE the initialization is in the middle of a bunch of variable 
declarations at the top)


--Dan