8219902: C2: MemNode::can_see_stored_value() ignores casts which carry control dependency

Reviewed-by: kvn

src/hotspot/share/opto/memnode.cpp

@@ -1047,11 +1047,11 @@ Node* MemNode::can_see_stored_value(Node* st, PhaseTransform* phase) const {
         // Try harder before giving up. Unify base pointers with casts (e.g., raw/non-raw pointers).
         intptr_t st_off = 0;
         Node* st_base = AddPNode::Ideal_base_and_offset(st_adr, phase, st_off);
-        if (ld_base == NULL)                        return NULL;
-        if (st_base == NULL)                        return NULL;
-        if (ld_base->uncast() != st_base->uncast()) return NULL;
-        if (ld_off != st_off)                       return NULL;
-        if (ld_off == Type::OffsetBot)              return NULL;
+        if (ld_base == NULL)                                   return NULL;
+        if (st_base == NULL)                                   return NULL;
+        if (!ld_base->eqv_uncast(st_base, /*keep_deps=*/true)) return NULL;
+        if (ld_off != st_off)                                  return NULL;
+        if (ld_off == Type::OffsetBot)                         return NULL;
         // Same base, same offset.
         // Possible improvement for arrays: check index value instead of absolute offset.
 
@@ -1062,6 +1062,7 @@ Node* MemNode::can_see_stored_value(Node* st, PhaseTransform* phase) const {
         // (Actually, we haven't yet proven the Q's are the same.)
         // In other words, we are loading from a casted version of
         // the same pointer-and-offset that we stored to.
+        // Casted version may carry a dependency and it is respected.
         // Thus, we are able to replace L by V.
       }
       // Now prove that we have a LoadQ matched to a StoreQ, for some Q.

src/hotspot/share/opto/node.cpp

@@ -891,13 +891,15 @@ int Node::disconnect_inputs(Node *n, Compile* C) {
 //-----------------------------uncast---------------------------------------
 // %%% Temporary, until we sort out CheckCastPP vs. CastPP.
 // Strip away casting.  (It is depth-limited.)
-Node* Node::uncast() const {
+// Optionally, keep casts with dependencies.
+Node* Node::uncast(bool keep_deps) const {
   // Should be inline:
   //return is_ConstraintCast() ? uncast_helper(this) : (Node*) this;
-  if (is_ConstraintCast())
-    return uncast_helper(this);
-  else
+  if (is_ConstraintCast()) {
+    return uncast_helper(this, keep_deps);
+  } else {
     return (Node*) this;
+  }
 }
 
 // Find out of current node that matches opcode.
@@ -929,7 +931,7 @@ bool Node::has_out_with(int opcode1, int opcode2, int opcode3, int opcode4) {
 
 
 //---------------------------uncast_helper-------------------------------------
-Node* Node::uncast_helper(const Node* p) {
+Node* Node::uncast_helper(const Node* p, bool keep_deps) {
 #ifdef ASSERT
   uint depth_count = 0;
   const Node* orig_p = p;
@@ -947,6 +949,9 @@ Node* Node::uncast_helper(const Node* p) {
     if (p == NULL || p->req() != 2) {
       break;
     } else if (p->is_ConstraintCast()) {
+      if (keep_deps && p->as_ConstraintCast()->carry_dependency()) {
+        break; // stop at casts with dependencies
+      }
       p = p->in(1);
     } else {
       break;

src/hotspot/share/opto/node.hpp

@@ -456,10 +456,10 @@ protected:
   void setup_is_top();
 
   // Strip away casting.  (It is depth-limited.)
-  Node* uncast() const;
+  Node* uncast(bool keep_deps = false) const;
   // Return whether two Nodes are equivalent, after stripping casting.
-  bool eqv_uncast(const Node* n) const {
-    return (this->uncast() == n->uncast());
+  bool eqv_uncast(const Node* n, bool keep_deps = false) const {
+    return (this->uncast(keep_deps) == n->uncast(keep_deps));
   }
 
   // Find out of current node that matches opcode.
@@ -470,7 +470,7 @@ protected:
   bool has_out_with(int opcode1, int opcode2, int opcode3, int opcode4);
 
 private:
-  static Node* uncast_helper(const Node* n);
+  static Node* uncast_helper(const Node* n, bool keep_deps);
 
   // Add an output edge to the end of the list
   void add_out( Node *n ) {