On Thu, Sep 27, 2012 at 08:04:58PM +0200, Uros Bizjak wrote:
> After some off-line discussion with Richard, attached is v2 of the patch.
>
> 2012-09-27 Uros Bizjak <ubiz...@gmail.com>
>
> PR rtl-optimization/54457
> * simplify-rtx.c (simplify_subreg):
> Simplify (subreg:SI (op:DI ((x:DI) (y:DI)), 0)
> to (op:SI (subreg:SI (x:DI) 0) (subreg:SI (x:DI) 0)).
Is that a good idea even for WORD_REGISTER_OPERATIONS targets?
> --- simplify-rtx.c (revision 191808)
> +++ simplify-rtx.c (working copy)
> @@ -5689,6 +5689,28 @@ simplify_subreg (enum machine_mode outermode, rtx
> return CONST0_RTX (outermode);
> }
>
> + /* Simplify (subreg:SI (op:DI ((x:DI) (y:DI)), 0)
> + to (op:SI (subreg:SI (x:DI) 0) (subreg:SI (x:DI) 0)), where
> + the outer subreg is effectively a truncation to the original mode. */
> + if ((GET_CODE (op) == PLUS
> + || GET_CODE (op) == MINUS
> + || GET_CODE (op) == MULT)
> + && SCALAR_INT_MODE_P (outermode)
> + && SCALAR_INT_MODE_P (innermode)
> + && GET_MODE_PRECISION (outermode) < GET_MODE_PRECISION (innermode)
> + && byte == subreg_lowpart_offset (outermode, innermode))
> + {
> + rtx op0 = simplify_gen_subreg (outermode, XEXP (op, 0),
> + innermode, byte);
> + if (op0)
> + {
> + rtx op1 = simplify_gen_subreg (outermode, XEXP (op, 1),
> + innermode, byte);
> + if (op1)
> + return simplify_gen_binary (GET_CODE (op), outermode, op0, op1);
> + }
> + }
> +
> /* Simplify (subreg:QI (lshiftrt:SI (sign_extend:SI (x:QI)) C), 0) into
> to (ashiftrt:QI (x:QI) C), where C is a suitable small constant and
> the outer subreg is effectively a truncation to the original mode. */
Jakub
