https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122653
Bug ID: 122653
Summary: SCEV does not handle POINTER_DIFF_EXPR
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Target Milestone: ---
extern char a[];
int foo ()
{
int cnt = 0;
char *aend = a + 32;
char *a0 = a;
do
{
a0 = a0 + 16;
cnt++;
}
while (aend - a0 > 12);
return cnt;
}
for this testcase we fail number of iteration analysis because
<bb 3> [local count: 1073741824]:
# a0_3 = PHI <&a(2), a0_4(5)>
...
a0_4 = a0_3 + 16;
...
_1 = &MEM <char[<unknown>]> [(void *)&a + 32B] - a0_4;
if (_1 > 12)
we already fail to analyze the scalar evolution of _1. SCEV handles
MINUS_EXPR, but only when the SSA cycle is on the first operand, but
not POINTER_DIFF_EXPR. So a similar case can be probably constructed
with integer MINUS_EXPR.
