[RFA] [PATCH][PR tree-optimization/59749] Fix recently introduced ree bug

Jakub Jelinek jakub@redhat.com
Thu Jan 16 22:07:00 GMT 2014

On Thu, Jan 16, 2014 at 02:31:09PM -0700, Jeff Law wrote:
> +2014-01-16  Jeff Law  <law@redhat.com>
> +
> +	* ree.c (combine_set_extension): Correct test for changing number
> +	of hard registers when widening a reaching definition.
> +
>  2014-01-16  Bernd Schmidt  <bernds@codesourcery.com>
>  	PR middle-end/56791
> diff --git a/gcc/ree.c b/gcc/ree.c
> index 19d821c..96cddd2 100644
> --- a/gcc/ree.c
> +++ b/gcc/ree.c
> @@ -300,7 +300,8 @@ combine_set_extension (ext_cand *cand, rtx curr_insn, rtx *orig_set)
>    /* We're going to be widening the result of DEF_INSN, ensure that doing so
>       doesn't change the number of hard registers needed for the result.  */
>    if (HARD_REGNO_NREGS (REGNO (new_reg), cand->mode)
> -      != HARD_REGNO_NREGS (REGNO (orig_src), GET_MODE (SET_DEST (*orig_set))))
> +      != HARD_REGNO_NREGS (REGNO (SET_DEST (*orig_set)),
> +			   GET_MODE (SET_DEST (*orig_set))))

Shouldn't that be:
    if (HARD_REGNO_NREGS (REGNO (new_reg), cand->mode)
	!= HARD_REGNO_NREGS (REGNO (new_reg), GET_MODE (SET_DEST (*orig_set))))

I mean, for the !copy_needed case it is obviously the same thing (and that
is what triggers in the testcase), but don't we generally want to check if
the same hard register in a wider mode will not occupy more registers, and
in particular the hard register we are considering to use on the lhs of the
defining insn (i.e. new_reg)?

Of course usually HARD_REGNO_NREGS will be the same for the same mode and
different GPR, so it would be really hard to create a testcase.


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