CCP: handle division by a power of 2 as a right shift.
Commit Message
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?
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(-)
Comments
On Tue, Nov 8, 2022 at 3:25 PM Aldy Hernandez <aldyh@redhat.com> 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
>
@@ -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;
}
@@ -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)))
{