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 :