https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110377
Bug ID: 110377
Summary: Early VRP and IPA-PROP should work out value ranges
from __builtin_unreacahble
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: hubicka at gcc dot gnu.org
Target Milestone: ---
In the following testcase
void test2(int);
void
test(int n)
{
if (n > 5)
__builtin_unreachable ();
test2(n);
}
we should work out that value range of n passed to test2 is [INT_MIN,4].
This would help optimizing some code in libstdc++, which now uses similar
constructs to ensure known value ranges.
I think it is a common case where such unreachable test can be retrofited to
the SSA_NAME based on the fact that program can not terminate between
definition and the conditional.
We currently get:
function test/0 parameter descriptors:
param #0 n used undescribed_use
Jump functions of caller test/0:
callsite test/0 -> test2/2 :
param 0: PASS THROUGH: 0, op nop_expr
value: 0x0, mask:
0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
Unknown VR
callsite test/0 -> __builtin_unreachable/1 :
