[PATCH, 2/2][nvptx, PR83589] Workaround for branch-around-nothing JIT bug

[Jakub Jelinek]

On Wed, Jan 24, 2018 at 11:41:45AM +0100, Tom de Vries wrote:
> +/* Insert a dummy ptx insn when encountering a branch to a label with no ptx
> +   insn inbetween the branch and the label.  This works around a JIT bug
> +   observed at driver version 384.111, at -O0 for sm_50.  */
> +
> +static void
> +prevent_branch_around_nothing (void)
> +{
> +  rtx_insn *seen_label = 0;
> +    for (rtx_insn *insn = get_insns (); insn; insn = NEXT_INSN (insn))
> +      {
> +	if (seen_label == 0)
> +	  {
> +	    if (INSN_P (insn) && condjump_p (insn))
> +	      seen_label = label_ref_label (nvptx_condjump_label (insn, false));
> +
> +	    continue;
> +	  }
> +
> +	if (NOTE_P (insn))
> +	  continue;

I'm afraid for review I don't know the backend enough.
I'd just suggest using NULL instead of 0 for pointers, i.e. clearing
seen_label or comparisons of seen_label against NULL, and wonder if
DEBUG_INSNs are guaranteed not to appear here.  If not, you'd need to
skip them too.

	Jakub