JDK-8147853 : "assert(t->meet(t0) == t) failed: Not monotonic" with sun/util/calendar/zi/TestZoneInfo310.java
  • Type: Bug
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 9
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2016-01-20
  • Updated: 2016-02-11
  • Resolved: 2016-01-26
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JDK 9
9 b105Fixed
Related Reports
Relates :  
JDK-8145322 - Code generated from unsafe loops can be slightly improved
Description
JDK-8145322 causes sun/util/calendar/zi/TestZoneInfo310.java  with:

assert(t->meet(t0) == t) failed: Not monotonic

Undoing the change from PhiNode::Value() causes the failure to disappear.
Comments
During CCP, a Phi for the induction variable of a CountedLoop is processed repeatedly while the type of the backedge control is top so only the loop entry input is considered for computing the Phi���s type. The loop entry first has type int:1..3 so the Phi���s type is int:1..3 then it has type int:1..4 so the Phi���s type is int:1..4 then it has type int:1..5:www so the Phi���s type is int:1..5:www then it has type int:1..6:www so the Phi���s type is saturated to int:1..max-1:www The backedge control���s type is changed to non-top and the type of the Phi is recomputed. This time the special code for counted loop in PhiNode::Value(): CountedLoopNode* l = r->is_CountedLoop() ? r->as_CountedLoop() : NULL; if (l && l->can_be_counted_loop(phase) && ((const Node*)l->phi() == this)) { // Trip counted loop! // protect against init_trip() or limit() returning NULL const Node *init = l->init_trip(); const Node *limit = l->limit(); const Node* stride = l->stride(); if (init != NULL && limit != NULL && stride != NULL) { const TypeInt* lo = phase->type(init)->isa_int(); const TypeInt* hi = phase->type(limit)->isa_int(); const TypeInt* stride_t = phase->type(stride)->isa_int(); if (lo != NULL && hi != NULL && stride_t != NULL) { // Dying loops might have TOP here assert(stride_t->_hi >= stride_t->_lo, "bad stride type"); const Type* res = NULL; if (stride_t->_hi < 0) { // Down-counter loop swap(lo, hi); return TypeInt::make(MIN2(lo->_lo, hi->_lo) , hi->_hi, 3); } else if (stride_t->_lo >= 0) { return TypeInt::make(lo->_lo, MAX2(lo->_hi, hi->_hi), 3); } } } } kicks in and it computes a type of: int:1..8:www. The type of the Phi was narrowed and the assert fires.
26-01-2016
regarding lack of test case: processing order of nodes during CCP matter and is hard to control from a test case
26-01-2016