@@ -1371,10 +1371,27 @@ inline int Parse::repush_if_args() {
13711371 return bc_depth;
13721372}
13731373
1374+ // Used by StressUnstableIfTraps
1375+ static volatile int _trap_stress_counter = 0 ;
1376+
1377+ void Parse::increment_trap_stress_counter (Node*& counter, Node*& incr_store) {
1378+ Node* counter_addr = makecon (TypeRawPtr::make ((address)&_trap_stress_counter));
1379+ counter = make_load (control (), counter_addr, TypeInt::INT, T_INT, Compile::AliasIdxRaw, MemNode::unordered);
1380+ counter = _gvn.transform (new AddINode (counter, intcon (1 )));
1381+ incr_store = store_to_memory (control (), counter_addr, counter, T_INT, Compile::AliasIdxRaw, MemNode::unordered);
1382+ }
1383+
13741384// ----------------------------------do_ifnull----------------------------------
13751385void Parse::do_ifnull (BoolTest::mask btest, Node *c) {
13761386 int target_bci = iter ().get_dest ();
13771387
1388+ Node* counter = nullptr ;
1389+ Node* incr_store = nullptr ;
1390+ bool do_stress_trap = StressUnstableIfTraps && ((C->random () % 2 ) == 0 );
1391+ if (do_stress_trap) {
1392+ increment_trap_stress_counter (counter, incr_store);
1393+ }
1394+
13781395 Block* branch_block = successor_for_bci (target_bci);
13791396 Block* next_block = successor_for_bci (iter ().next_bci ());
13801397
@@ -1439,6 +1456,10 @@ void Parse::do_ifnull(BoolTest::mask btest, Node *c) {
14391456 } else { // Path is live.
14401457 adjust_map_after_if (BoolTest (btest).negate (), c, 1.0 -prob, next_block);
14411458 }
1459+
1460+ if (do_stress_trap) {
1461+ stress_trap (iff, counter, incr_store);
1462+ }
14421463}
14431464
14441465// ------------------------------------do_if------------------------------------
@@ -1468,6 +1489,13 @@ void Parse::do_if(BoolTest::mask btest, Node* c) {
14681489 return ;
14691490 }
14701491
1492+ Node* counter = nullptr ;
1493+ Node* incr_store = nullptr ;
1494+ bool do_stress_trap = StressUnstableIfTraps && ((C->random () % 2 ) == 0 );
1495+ if (do_stress_trap) {
1496+ increment_trap_stress_counter (counter, incr_store);
1497+ }
1498+
14711499 // Sanity check the probability value
14721500 assert (0 .0f < prob && prob < 1 .0f ," Bad probability in Parser"
14731501
@@ -1550,9 +1578,58 @@ void Parse::do_if(BoolTest::mask btest, Node* c) {
15501578 } else {
15511579 adjust_map_after_if (untaken_btest, c, untaken_prob, next_block);
15521580 }
1581+
1582+ if (do_stress_trap) {
1583+ stress_trap (iff, counter, incr_store);
1584+ }
1585+ }
1586+
1587+ // Force unstable if traps to be taken randomly to trigger intermittent bugs such as incorrect debug information.
1588+ // Add another if before the unstable if that checks a "random" condition at runtime (a simple shared counter) and
1589+ // then either takes the trap or executes the original, unstable if.
1590+ void Parse::stress_trap (IfNode* orig_iff, Node* counter, Node* incr_store) {
1591+ // Search for an unstable if trap
1592+ CallStaticJavaNode* trap = nullptr ;
1593+ assert (orig_iff->Opcode () == Op_If && orig_iff->outcnt () == 2 , " malformed if"
1594+ ProjNode* trap_proj = orig_iff->uncommon_trap_proj (trap, Deoptimization::Reason_unstable_if);
1595+ if (trap == nullptr || !trap->jvms ()->should_reexecute ()) {
1596+ // No suitable trap found. Remove unused counter load and increment.
1597+ C->gvn_replace_by (incr_store, incr_store->in (MemNode::Memory));
1598+ return ;
1599+ }
1600+
1601+ // Remove trap from optimization list since we add another path to the trap.
1602+ bool success = C->remove_unstable_if_trap (trap, true );
1603+ assert (success, " Trap already modified"
1604+
1605+ // Add a check before the original if that will trap with a certain frequency and execute the original if otherwise
1606+ int freq_log = (C->random () % 31 ) + 1 ; // Random logarithmic frequency in [1, 31]
1607+ Node* mask = intcon (right_n_bits (freq_log));
1608+ counter = _gvn.transform (new AndINode (counter, mask));
1609+ Node* cmp = _gvn.transform (new CmpINode (counter, intcon (0 )));
1610+ Node* bol = _gvn.transform (new BoolNode (cmp, BoolTest::mask::eq));
1611+ IfNode* iff = _gvn.transform (new IfNode (orig_iff->in (0 ), bol, orig_iff->_prob , orig_iff->_fcnt ))->as_If ();
1612+ Node* if_true = _gvn.transform (new IfTrueNode (iff));
1613+ Node* if_false = _gvn.transform (new IfFalseNode (iff));
1614+ assert (!if_true->is_top () && !if_false->is_top (), " trap always / never taken"
1615+
1616+ // Trap
1617+ assert (trap_proj->outcnt () == 1 , " some other nodes are dependent on the trap projection"
1618+
1619+ Node* trap_region = new RegionNode (3 );
1620+ trap_region->set_req (1 , trap_proj);
1621+ trap_region->set_req (2 , if_true);
1622+ trap->set_req (0 , _gvn.transform (trap_region));
1623+
1624+ // Don't trap, execute original if
1625+ orig_iff->set_req (0 , if_false);
15531626}
15541627
15551628bool Parse::path_is_suitable_for_uncommon_trap (float prob) const {
1629+ // Randomly skip emitting an uncommon trap
1630+ if (StressUnstableIfTraps && ((C->random () % 2 ) == 0 )) {
1631+ return false ;
1632+ }
15561633 // Don't want to speculate on uncommon traps when running with -Xcomp
15571634 if (!UseInterpreter) {
15581635 return false ;
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