[COMMITTED] Improve multiplication by powers of 2 in range-ops.
Checks
Commit Message
For unsigned numbers, multiplication by X, where X is a power of 2 is
[0,0][X,+INF].
This patch causes a regression to g++.dg/pr71488.C where
-Wstringop-overflow gets the same IL as before, but better ranges
cause it to issue a bogus warning. I will create a PR with some
notes.
No discernible changes in performance.
Tested on x86-64 Linux.
PR tree-optimization/55157
gcc/ChangeLog:
* range-op.cc (operator_mult::wi_fold): Optimize multiplications
by powers of 2.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/pr55157.c: New test.
---
gcc/range-op.cc | 16 ++++++++++++++--
gcc/testsuite/gcc.dg/tree-ssa/pr55157.c | 19 +++++++++++++++++++
2 files changed, 33 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr55157.c
Comments
On Mon, Nov 7, 2022 at 8:59 PM Aldy Hernandez <aldyh@redhat.com> wrote:
>
> For unsigned numbers, multiplication by X, where X is a power of 2 is
> [0,0][X,+INF].
>
> This patch causes a regression to g++.dg/pr71488.C where
> -Wstringop-overflow gets the same IL as before, but better ranges
> cause it to issue a bogus warning. I will create a PR with some
> notes.
PR107561
@@ -1910,8 +1910,20 @@ operator_mult::wi_fold (irange &r, tree type,
// diff = max - min
prod2 = prod3 - prod0;
if (wi::geu_p (prod2, sizem1))
- // The range covers all values.
- r.set_varying (type);
+ {
+ // Multiplying by X, where X is a power of 2 is [0,0][X,+INF].
+ if (TYPE_UNSIGNED (type) && rh_lb == rh_ub
+ && wi::exact_log2 (rh_lb) != -1 && prec > 1)
+ {
+ r.set (type, rh_lb, wi::max_value (prec, sign));
+ int_range<2> zero;
+ zero.set_zero (type);
+ r.union_ (zero);
+ }
+ else
+ // The range covers all values.
+ r.set_varying (type);
+ }
else
{
wide_int new_lb = wide_int::from (prod0, prec, sign);
new file mode 100644
@@ -0,0 +1,19 @@
+// { dg-do compile }
+// { dg-options "-O2 -fdump-tree-evrp" }
+
+void gg(void);
+int f(unsigned t)
+{
+ unsigned g = t*16;
+ if (g==0) return 1;
+ gg();
+ gg();
+ gg();
+ gg();
+ gg();
+ gg();
+ if (g<=4) return 1;
+ return 0;
+}
+
+// { dg-final { scan-tree-dump-times " if " 1 "evrp" } }