On Fri, Dec 09, 2016 at 04:23:44PM +0100, Dominik Vogt wrote:
> 0001-*
>
> Deal with mode expanding zero_extracts in change_zero_ext. The
> patch looks good to me, but not sure whether endianness is
> handled properly. Is the second argument of gen_rtx_SUBREG
> correct?
> >From 600ed3dadd5bc2568ab53be8466686abaf27ff3f Mon Sep 17 00:00:00 2001
> From: Dominik Vogt <v...@linux.vnet.ibm.com>
> Date: Fri, 9 Dec 2016 02:48:30 +0100
> Subject: [PATCH 1/2] combine: Handle mode expanding zero_extracts in
> change_zero_ext.
>
> Example:
>
> (zero_extract:DI (reg:SI)
> (const_int 24)
> (const_int 0))
>
> -->
>
> (and:DI (subreg:DI (lshiftrt:SI (reg:SI) (const_int 8))
> 0)
> (const_int 16777215))
> ---
> gcc/combine.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/combine.c b/gcc/combine.c
> index b429453..e14a08f 100644
> --- a/gcc/combine.c
> +++ b/gcc/combine.c
> @@ -11237,18 +11237,24 @@ change_zero_ext (rtx pat)
> if (GET_CODE (x) == ZERO_EXTRACT
> && CONST_INT_P (XEXP (x, 1))
> && CONST_INT_P (XEXP (x, 2))
> - && GET_MODE (XEXP (x, 0)) == mode)
> + && (GET_MODE (XEXP (x, 0)) == mode
> + || GET_MODE_PRECISION (GET_MODE (XEXP (x, 0)))
> + < GET_MODE_PRECISION (mode)))
If you make this <= you can collapse the two cases into one.
> {
> + machine_mode inner_mode = GET_MODE (XEXP (x, 0));
> +
> size = INTVAL (XEXP (x, 1));
>
> int start = INTVAL (XEXP (x, 2));
> if (BITS_BIG_ENDIAN)
> - start = GET_MODE_PRECISION (mode) - size - start;
> + start = GET_MODE_PRECISION (inner_mode) - size - start;
>
> if (start)
> - x = gen_rtx_LSHIFTRT (mode, XEXP (x, 0), GEN_INT (start));
> + x = gen_rtx_LSHIFTRT (inner_mode, XEXP (x, 0), GEN_INT (start));
> else
> x = XEXP (x, 0);
> + if (mode != inner_mode)
> + x = gen_rtx_SUBREG (mode, x, 0);
gen_lowpart_SUBREG instead? It's easier to read, and code a little
further down does the same thing.
Okay for trunk with those changes (did you bootstrap+regcheck this
already?) Thanks,
Segher
