out of bounds access in insn-automata.c

[Bernd Schmidt]

On 03/23/2016 07:32 AM, Aldy Hernandez wrote:
>
> int
> maximal_insn_latency (rtx insn)
> {
>    int insn_code;
>
>    if (insn == 0)
>      insn_code = DFA__ADVANCE_CYCLE;
>
>
>    else
>      {
>        insn_code = dfa_insn_code (as_a <rtx_insn *> (insn));
>        if (insn_code > DFA__ADVANCE_CYCLE)
>          return 0;
>      }
>    return internal_maximal_insn_latency (insn_code, insn);
> }
>
> In the case where insn==0, insn_code is set to the size of
> default_latencies[] which will get accessed in the return.
>
> Does insn==0 never happen?

I suspect it never happens in this function. I'd add a gcc_assert to 
that effect and try a bootstrap/test. Hmm, it seems to be a sel-sched 
only thing so a normal bootstrap would be meaningless, but from the 
context it looks fairly clearly like insn is always nonnull.

It looks like this block of code is written by a helper function that is 
really intended for other purposes than for maximal_insn_latency. Might 
be worth changing to
  int insn_code = dfa_insn_code (as_a <rtx_insn *> (insn));
  gcc_assert (insn_code <= DFA__ADVANCE_CYCLE);


Bernd