FreeChainXenon/gcc
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Improve multiplication by powers of 2 in range-ops.

Browse source 
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.
This commit is contained in:
Aldy Hernandez 2022-11-04 22:24:42 +01:00
parent 03ed4e57e3
commit a239a63f86
2 changed files with 33 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

16
gcc/range-op.cc
View file

@ -1911,8 +1911,20 @@ 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);

19
gcc/testsuite/gcc.dg/tree-ssa/pr55157.c Normal file
View file

@ -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" } }