https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108748
Bug ID: 108748
Summary: Enhancement: track ranges of poly_int indeterminates
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rsandifo at gcc dot gnu.org
Target Milestone: ---
I've no idea how this would work in practice, just recording it as an
idea/TODO, but: it would be nice if code guarded by a range check on a poly_int
could be optimised for the implied range of the indeterminates. Maybe ranger
could be taught to do this.
One simple example is:
#include <arm_sve.h>
uint64_t foo(uint64_t x)
{
if (svcntb() == 2)
x += svcntb() * 100;
return x;
}
which generates:
cntb x1
cmp x1, 2
cntd x1, all, mul #3
lsl x1, x1, 8
add x1, x0, x1
incb x1, all, mul #4
csel x0, x1, x0, eq
ret
whereas the equivalent:
#include <arm_sve.h>
uint64_t foo(uint64_t x)
{
if (svcntb() == 2)
x += 200;
return x;
}
generates:
cntb x1
cmp x1, 2
add x1, x0, 200
csel x0, x1, x0, eq
ret
A more realistic use case would be to guard a block of code with a particular
VL in the hope that the code would be optimised for that VL.
