Check hash before and after Ideal call and fix phinode

src/hotspot/share/opto/c2_globals.hpp

@@ -694,7 +694,9 @@
           "Print progress during Iterative Global Value Numbering")         \
                                                                             \
   develop(uint, VerifyIterativeGVN, 0,                                      \
-          "Verify Iterative Global Value Numbering =EDCBA, with:"           \
+          "Verify Iterative Global Value Numbering =FEDCBA, with:"          \
+          "  F: verify Node::Ideal does not return nullptr if the node"     \
+                "hash has changed"                                          \
           "  E: verify node specific invariants"                            \
           "  D: verify Node::Identity did not miss opportunities"           \
           "  C: verify Node::Ideal did not miss opportunities"              \

src/hotspot/share/opto/cfgnode.cpp

@@ -2243,7 +2243,7 @@ Node *PhiNode::Ideal(PhaseGVN *phase, bool can_reshape) {
     PhaseIterGVN* igvn = phase->is_IterGVN();
     if (wait_for_cast_input_igvn(igvn)) {
       igvn->_worklist.push(this);
-      return nullptr;
+      return progress;
     }
     uncasted = true;
     uin = unique_input(phase, true);
@@ -2320,6 +2320,7 @@ Node *PhiNode::Ideal(PhaseGVN *phase, bool can_reshape) {
       PhaseIterGVN* igvn = phase->is_IterGVN();
       for (uint i = 1; i < req(); i++) {
         set_req_X(i, cast, igvn);
+        progress = this;
       }
       uin = cast;
     }
@@ -2338,7 +2339,7 @@ Node *PhiNode::Ideal(PhaseGVN *phase, bool can_reshape) {
 #endif
     // Identity may not return the expected uin, if it has to wait for the region, in irreducible case
     assert(ident == uin || ident->is_top() || must_wait_for_region_in_irreducible_loop(phase), "Identity must clean this up");
-    return nullptr;
+    return progress;
   }
 
   Node* opt = nullptr;
@@ -2529,7 +2530,7 @@ Node *PhiNode::Ideal(PhaseGVN *phase, bool can_reshape) {
       // Phi references itself through all other inputs then splitting the
       // Phi through memory merges would create dead loop at later stage.
       if (ii == top) {
-        return nullptr; // Delay optimization until graph is cleaned.
+        return progress; // Delay optimization until graph is cleaned.
       }
       if (ii->is_MergeMem()) {
         MergeMemNode* n = ii->as_MergeMem();

src/hotspot/share/opto/phaseX.cpp

@@ -2126,9 +2126,15 @@ Node *PhaseIterGVN::transform_old(Node* n) {
   DEBUG_ONLY(dead_loop_check(k);)
   DEBUG_ONLY(bool is_new = (k->outcnt() == 0);)
   C->remove_modified_node(k);
+#ifndef PRODUCT
+  uint hash_before = is_verify_Ideal_return() ? k->hash() : 0;
+#endif
   Node* i = apply_ideal(k, /*can_reshape=*/true);
   assert(i != k || is_new || i->outcnt() > 0, "don't return dead nodes");
 #ifndef PRODUCT
+  if (is_verify_Ideal_return()) {
+    assert(k->outcnt() == 0 || i != nullptr || hash_before == k->hash(), "hash changed after Ideal returned nullptr for %s", k->Name());
+  }
   verify_step(k);
 #endif
 
@@ -2152,9 +2158,15 @@ Node *PhaseIterGVN::transform_old(Node* n) {
     // Try idealizing again
     DEBUG_ONLY(is_new = (k->outcnt() == 0);)
     C->remove_modified_node(k);
+#ifndef PRODUCT
+    uint hash_before = is_verify_Ideal_return() ? k->hash() : 0;
+#endif
     i = apply_ideal(k, /*can_reshape=*/true);
     assert(i != k || is_new || (i->outcnt() > 0), "don't return dead nodes");
 #ifndef PRODUCT
+    if (is_verify_Ideal_return()) {
+      assert(k->outcnt() == 0 || i != nullptr || hash_before == k->hash(), "hash changed after Ideal returned nullptr for %s", k->Name());
+    }
     verify_step(k);
 #endif
     DEBUG_ONLY(loop_count++;)

src/hotspot/share/opto/phaseX.hpp

@@ -621,6 +621,10 @@ public:
     // '-XX:VerifyIterativeGVN=10000'
     return ((VerifyIterativeGVN % 100000) / 10000) == 1;
   }
+  static bool is_verify_Ideal_return() {
+    // '-XX:VerifyIterativeGVN=100000'
+    return ((VerifyIterativeGVN % 1000000) / 100000) == 1;
+  }
 protected:
   // Sub-quadratic implementation of '-XX:VerifyIterativeGVN=1' (Use-Def verification).
   julong _verify_counter;

src/hotspot/share/runtime/flags/jvmFlagConstraintsCompiler.cpp

@@ -306,7 +306,7 @@ JVMFlag::Error TypeProfileLevelConstraintFunc(uint value, bool verbose) {
 }
 
 JVMFlag::Error VerifyIterativeGVNConstraintFunc(uint value, bool verbose) {
-  const int max_modes = 5;
+  const int max_modes = 6;
   uint original_value = value;
   for (int i = 0; i < max_modes; i++) {
     if (value % 10 > 1) {