On Fri, 10 Jan 2025, Alexandre Oliva wrote:
>
> If fold_truth_andor_for_ifcombine applies a mask to an xor, say
> because the result of the xor is compared with a power of two [minus
> one], we have to apply the same mask when processing both the left-
> and right-hand xor paths for the transformation to be sound. Arrange
> for decode_field_reference to propagate the incoming mask along with
> the expression to the right-hand operand.
>
> Don't require the right-hand xor operand to be a constant, that was a
> cut&pasto.
>
> Regstrapped on x86_64-linux-gnu. Ok to install?
OK.
Richard.
>
> for gcc/ChangeLog
>
> * gimple-fold.cc (decode_field_reference): Add xor_pand_mask.
> Propagate pand_mask to the right-hand xor operand. Don't
> require the right-hand xor operand to be a constant.
> (fold_truth_andor_for_ifcombine): Pass right-hand mask when
> appropriate.
> ---
> gcc/gimple-fold.cc | 23 +++++++++++++----------
> 1 file changed, 13 insertions(+), 10 deletions(-)
>
> diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
> index d95f04213ee40..0ad92de3a218f 100644
> --- a/gcc/gimple-fold.cc
> +++ b/gcc/gimple-fold.cc
> @@ -7519,8 +7519,9 @@ gimple_binop_def_p (enum tree_code code, tree t, tree
> op[2])
>
> *XOR_P is to be FALSE if EXP might be a XOR used in a compare, in which
> case, if XOR_CMP_OP is a zero constant, it will be overridden with *PEXP,
> - *XOR_P will be set to TRUE, and the left-hand operand of the XOR will be
> - decoded. If *XOR_P is TRUE, XOR_CMP_OP is supposed to be NULL, and then
> the
> + *XOR_P will be set to TRUE, *XOR_PAND_MASK will be copied from *PAND_MASK,
> + and the left-hand operand of the XOR will be decoded. If *XOR_P is TRUE,
> + XOR_CMP_OP and XOR_PAND_MASK are supposed to be NULL, and then the
> right-hand operand of the XOR will be decoded.
>
> *LOAD is set to the load stmt of the innermost reference, if any,
> @@ -7537,7 +7538,7 @@ decode_field_reference (tree *pexp, HOST_WIDE_INT
> *pbitsize,
> HOST_WIDE_INT *pbitpos,
> bool *punsignedp, bool *preversep, bool *pvolatilep,
> wide_int *pand_mask, bool *psignbit,
> - bool *xor_p, tree *xor_cmp_op,
> + bool *xor_p, tree *xor_cmp_op, wide_int *xor_pand_mask,
> gimple **load, location_t loc[4])
> {
> tree exp = *pexp;
> @@ -7599,15 +7600,14 @@ decode_field_reference (tree *pexp, HOST_WIDE_INT
> *pbitsize,
> and_mask = *pand_mask;
>
> /* Turn (a ^ b) [!]= 0 into a [!]= b. */
> - if (xor_p && gimple_binop_def_p (BIT_XOR_EXPR, exp, res_ops)
> - && uniform_integer_cst_p (res_ops[1]))
> + if (xor_p && gimple_binop_def_p (BIT_XOR_EXPR, exp, res_ops))
> {
> /* No location recorded for this one, it's entirely subsumed by the
> compare. */
> if (*xor_p)
> {
> exp = res_ops[1];
> - gcc_checking_assert (!xor_cmp_op);
> + gcc_checking_assert (!xor_cmp_op && !xor_pand_mask);
> }
> else if (!xor_cmp_op)
> /* Not much we can do when xor appears in the right-hand compare
> @@ -7618,6 +7618,7 @@ decode_field_reference (tree *pexp, HOST_WIDE_INT
> *pbitsize,
> *xor_p = true;
> exp = res_ops[0];
> *xor_cmp_op = *pexp;
> + *xor_pand_mask = *pand_mask;
> }
> }
>
> @@ -8152,19 +8153,21 @@ fold_truth_andor_for_ifcombine (enum tree_code code,
> tree truth_type,
> bool l_xor = false, r_xor = false;
> ll_inner = decode_field_reference (&ll_arg, &ll_bitsize, &ll_bitpos,
> &ll_unsignedp, &ll_reversep, &volatilep,
> - &ll_and_mask, &ll_signbit, &l_xor, &lr_arg,
> + &ll_and_mask, &ll_signbit,
> + &l_xor, &lr_arg, &lr_and_mask,
> &ll_load, ll_loc);
> lr_inner = decode_field_reference (&lr_arg, &lr_bitsize, &lr_bitpos,
> &lr_unsignedp, &lr_reversep, &volatilep,
> - &lr_and_mask, &lr_signbit, &l_xor, 0,
> + &lr_and_mask, &lr_signbit, &l_xor, 0, 0,
> &lr_load, lr_loc);
> rl_inner = decode_field_reference (&rl_arg, &rl_bitsize, &rl_bitpos,
> &rl_unsignedp, &rl_reversep, &volatilep,
> - &rl_and_mask, &rl_signbit, &r_xor, &rr_arg,
> + &rl_and_mask, &rl_signbit,
> + &r_xor, &rr_arg, &rr_and_mask,
> &rl_load, rl_loc);
> rr_inner = decode_field_reference (&rr_arg, &rr_bitsize, &rr_bitpos,
> &rr_unsignedp, &rr_reversep, &volatilep,
> - &rr_and_mask, &rr_signbit, &r_xor, 0,
> + &rr_and_mask, &rr_signbit, &r_xor, 0, 0,
> &rr_load, rr_loc);
>
> /* It must be true that the inner operation on the lhs of each
>
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
