On Tue, Nov 8, 2022 at 3:25 PM Aldy Hernandez <[email protected]> wrote:
>
> We have some code in range-ops that sets better maybe nonzero bits for
> TRUNC_DIV_EXPR by a power of 2 than CCP does, by just shifting the
> mask. I'd like to offload this functionality into the CCP mask
> tracking code, which already does the right thing for right shifts.
>
> The testcase for this change is gcc.dg/tree-ssa/vrp123.c and
> gcc.dg/tree-ssa/pr107541.c.
>
> Tested on x86-64 Linux.
>
> OK?
LGTM
> gcc/ChangeLog:
>
> * range-op.cc (operator_div::fold_range): Call
> update_known_bitmask.
> * tree-ssa-ccp.cc (bit_value_binop): Handle divisions by powers of
> 2 as a right shift.
> ---
> gcc/range-op.cc | 18 +-----------------
> gcc/tree-ssa-ccp.cc | 12 ++++++++++++
> 2 files changed, 13 insertions(+), 17 deletions(-)
>
> diff --git a/gcc/range-op.cc b/gcc/range-op.cc
> index 846931ddcae..8ff5d5b4c78 100644
> --- a/gcc/range-op.cc
> +++ b/gcc/range-op.cc
> @@ -1995,23 +1995,7 @@ operator_div::fold_range (irange &r, tree type,
> if (!cross_product_operator::fold_range (r, type, lh, rh, trio))
> return false;
>
> - if (lh.undefined_p ())
> - return true;
> -
> - tree t;
> - if (code == TRUNC_DIV_EXPR
> - && rh.singleton_p (&t)
> - && !wi::neg_p (lh.lower_bound ()))
> - {
> - wide_int wi = wi::to_wide (t);
> - int shift = wi::exact_log2 (wi);
> - if (shift != -1)
> - {
> - wide_int nz = lh.get_nonzero_bits ();
> - nz = wi::rshift (nz, shift, TYPE_SIGN (type));
> - r.set_nonzero_bits (nz);
> - }
> - }
> + update_known_bitmask (r, code, lh, rh);
> return true;
> }
>
> diff --git a/gcc/tree-ssa-ccp.cc b/gcc/tree-ssa-ccp.cc
> index 3a4b6bc1118..2bcd90646f6 100644
> --- a/gcc/tree-ssa-ccp.cc
> +++ b/gcc/tree-ssa-ccp.cc
> @@ -1934,6 +1934,18 @@ bit_value_binop (enum tree_code code, signop sgn, int
> width,
> {
> widest_int r1max = r1val | r1mask;
> widest_int r2max = r2val | r2mask;
> + if (r2mask == 0 && !wi::neg_p (r1max))
> + {
> + widest_int shift = wi::exact_log2 (r2val);
> + if (shift != -1)
> + {
> + // Handle division by a power of 2 as an rshift.
> + bit_value_binop (RSHIFT_EXPR, sgn, width, val, mask,
> + r1type_sgn, r1type_precision, r1val, r1mask,
> + r2type_sgn, r2type_precision, shift, r2mask);
> + return;
> + }
> + }
> if (sgn == UNSIGNED
> || (!wi::neg_p (r1max) && !wi::neg_p (r2max)))
> {
> --
> 2.38.1
>
