8252583: Clean up unused phi-to-copy degradation mechanism

Remove unused notion of 'PhiNode-to-copy degradation', where PhiNodes can be
degraded to copies by setting their RegionNode to NULL. Remove corresponding
PhiNode::is_copy() test, which always returned NULL (false). Assert that
PhiNodes have an associated RegionNode in PhiNode::Ideal().

Reviewed-by: thartmann, kvn

src/hotspot/share/opto/addnode.cpp

@@ -91,9 +91,9 @@ static bool commute(Node *add, bool con_left, bool con_right) {
 
   PhiNode *phi;
   // Check for tight loop increments: Loop-phi of Add of loop-phi
-  if( in1->is_Phi() && (phi = in1->as_Phi()) && !phi->is_copy() && phi->region()->is_Loop() && phi->in(2)==add)
+  if (in1->is_Phi() && (phi = in1->as_Phi()) && phi->region()->is_Loop() && phi->in(2) == add)
     return false;
-  if( in2->is_Phi() && (phi = in2->as_Phi()) && !phi->is_copy() && phi->region()->is_Loop() && phi->in(2)==add){
+  if (in2->is_Phi() && (phi = in2->as_Phi()) && phi->region()->is_Loop() && phi->in(2) == add) {
     add->swap_edges(1, 2);
     return true;
   }

src/hotspot/share/opto/cfgnode.cpp

@@ -548,7 +548,7 @@ Node *RegionNode::Ideal(PhaseGVN *phase, bool can_reshape) {
             assert( igvn->eqv(n->in(0), this), "" );
             assert( n->req() == 2 &&  n->in(1) != NULL, "Only one data input expected" );
             // Break dead loop data path.
-            // Eagerly replace phis with top to avoid phis copies generation.
+            // Eagerly replace phis with top to avoid regionless phis.
             igvn->replace_node(n, top);
             if( max != outcnt() ) {
               progress = true;
@@ -589,7 +589,7 @@ Node *RegionNode::Ideal(PhaseGVN *phase, bool can_reshape) {
         assert( req() == 1, "no inputs expected" );
         // During IGVN phase such region will be subsumed by TOP node
         // so region's phis will have TOP as control node.
-        // Kill phis here to avoid it. PhiNode::is_copy() will be always false.
+        // Kill phis here to avoid it.
         // Also set other user's input to top.
         parent_ctrl = phase->C->top();
       } else {
@@ -604,7 +604,7 @@ Node *RegionNode::Ideal(PhaseGVN *phase, bool can_reshape) {
         Node* n = last_out(i);
         igvn->hash_delete(n); // Remove from worklist before modifying edges
         if( n->is_Phi() ) {   // Collapse all Phis
-          // Eagerly replace phis to avoid copies generation.
+          // Eagerly replace phis to avoid regionless phis.
           Node* in;
           if( cnt == 0 ) {
             assert( n->req() == 1, "No data inputs expected" );
@@ -1377,7 +1377,6 @@ Node* PhiNode::unique_input(PhaseTransform* phase, bool uncast) {
   //                      phi               /    --
 
   Node* r = in(0);                      // RegionNode
-  if (r == NULL)  return in(1);         // Already degraded to a Copy
   Node* input = NULL; // The unique direct input (maybe uncasted = ConstraintCasts removed)
 
   for (uint i = 1, cnt = req(); i < cnt; ++i) {
@@ -1861,11 +1860,8 @@ bool PhiNode::wait_for_region_igvn(PhaseGVN* phase) {
 // Return a node which is more "ideal" than the current node.  Must preserve
 // the CFG, but we can still strip out dead paths.
 Node *PhiNode::Ideal(PhaseGVN *phase, bool can_reshape) {
-  // The next should never happen after 6297035 fix.
-  if( is_copy() )               // Already degraded to a Copy ?
-    return NULL;                // No change
-
   Node *r = in(0);              // RegionNode
+  assert(r != NULL && r->is_Region(), "this phi must have a region");
   assert(r->in(0) == NULL || !r->in(0)->is_Root(), "not a specially hidden merge");
 
   // Note: During parsing, phis are often transformed before their regions.

src/hotspot/share/opto/cfgnode.hpp

@@ -115,9 +115,7 @@ class JProjNode : public ProjNode {
 //------------------------------PhiNode----------------------------------------
 // PhiNodes merge values from different Control paths.  Slot 0 points to the
 // controlling RegionNode.  Other slots map 1-for-1 with incoming control flow
-// paths to the RegionNode.  For speed reasons (to avoid another pass) we
-// can turn PhiNodes into copys in-place by NULL'ing out their RegionNode
-// input in slot 0.
+// paths to the RegionNode.
 class PhiNode : public TypeNode {
   friend class PhaseRenumberLive;
 
@@ -173,13 +171,6 @@ public:
   // Accessors
   RegionNode* region() const { Node* r = in(Region); assert(!r || r->is_Region(), ""); return (RegionNode*)r; }
 
-  Node* is_copy() const {
-    // The node is a real phi if _in[0] is a Region node.
-    DEBUG_ONLY(const Node* r = _in[Region];)
-    assert(r != NULL && r->is_Region(), "Not valid control");
-    return NULL;  // not a copy!
-  }
-
   bool is_tripcount() const;
 
   // Determine a unique non-trivial input, if any.

src/hotspot/share/opto/ifnode.cpp

@@ -86,7 +86,6 @@ static Node* split_if(IfNode *iff, PhaseIterGVN *igvn) {
   i1 = cmp->in(1);
   if( i1 == NULL || !i1->is_Phi() ) return NULL;
   PhiNode *phi = i1->as_Phi();
-  if( phi->is_copy() ) return NULL;
   Node *con2 = cmp->in(2);
   if( !con2->is_Con() ) return NULL;
   // See that the merge point contains some constants

src/hotspot/share/opto/loopnode.cpp

@@ -49,7 +49,7 @@
 // Determine if a node is a counted loop induction variable.
 // NOTE: The method is declared in "node.hpp".
 bool Node::is_cloop_ind_var() const {
-  return (is_Phi() && !as_Phi()->is_copy() &&
+  return (is_Phi() &&
           as_Phi()->region()->is_CountedLoop() &&
           as_Phi()->region()->as_CountedLoop()->phi() == this);
 }

src/hotspot/share/opto/memnode.cpp

@@ -4572,8 +4572,7 @@ Node *MergeMemNode::Ideal(PhaseGVN *phase, bool can_reshape) {
 
   Node*    phi_reg = NULL;
   uint     phi_len = (uint)-1;
-  if (phi_base != NULL && !phi_base->is_copy()) {
-    // do not examine phi if degraded to a copy
+  if (phi_base != NULL) {
     phi_reg = phi_base->region();
     phi_len = phi_base->req();
     // see if the phi is unfinished
@@ -4888,10 +4887,6 @@ bool MergeMemStream::match_memory(Node* mem, const MergeMemNode* mm, int idx) {
   if (mem == n)  return true;  // might be empty_memory()
   n = (idx == Compile::AliasIdxBot)? mm->base_memory(): mm->memory_at(idx);
   if (mem == n)  return true;
-  while (n->is_Phi() && (n = n->as_Phi()->is_copy()) != NULL) {
-    if (mem == n)  return true;
-    if (n == NULL)  break;
-  }
   return false;
 }
 #endif // !PRODUCT

src/hotspot/share/opto/subnode.cpp

@@ -124,7 +124,7 @@ static bool is_cloop_increment(Node* inc) {
   }
   const PhiNode* phi = inc->in(1)->as_Phi();
 
-  if (phi->is_copy() || !phi->region()->is_CountedLoop()) {
+  if (!phi->region()->is_CountedLoop()) {
     return false;
   }