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hotspot/src/share/vm/opto/loopUnswitch.cpp

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+/*
+ * Copyright 2006 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+#include "incls/_precompiled.incl"
+#include "incls/_loopUnswitch.cpp.incl"
+
+//================= Loop Unswitching =====================
+//
+// orig:                       transformed:
+//                               if (invariant-test) then
+//  loop                           loop
+//    stmt1                          stmt1
+//    if (invariant-test) then       stmt2
+//      stmt2                        stmt4
+//    else                         endloop
+//      stmt3                    else
+//    endif                        loop [clone]
+//    stmt4                          stmt1 [clone]
+//  endloop                          stmt3
+//                                   stmt4 [clone]
+//                                 endloop
+//                               endif
+//
+// Note: the "else" clause may be empty
+
+//------------------------------policy_unswitching-----------------------------
+// Return TRUE or FALSE if the loop should be unswitched
+// (ie. clone loop with an invariant test that does not exit the loop)
+bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {
+  if( !LoopUnswitching ) {
+    return false;
+  }
+  uint nodes_left = MaxNodeLimit - phase->C->unique();
+  if (2 * _body.size() > nodes_left) {
+    return false; // Too speculative if running low on nodes.
+  }
+  LoopNode* head = _head->as_Loop();
+  if (head->unswitch_count() + 1 > head->unswitch_max()) {
+    return false;
+  }
+  return phase->find_unswitching_candidate(this) != NULL;
+}
+
+//------------------------------find_unswitching_candidate-----------------------------
+// Find candidate "if" for unswitching
+IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {
+
+  // Find first invariant test that doesn't exit the loop
+  LoopNode *head = loop->_head->as_Loop();
+  IfNode* unswitch_iff = NULL;
+  Node* n = head->in(LoopNode::LoopBackControl);
+  while (n != head) {
+    Node* n_dom = idom(n);
+    if (n->is_Region()) {
+      if (n_dom->is_If()) {
+        IfNode* iff = n_dom->as_If();
+        if (iff->in(1)->is_Bool()) {
+          BoolNode* bol = iff->in(1)->as_Bool();
+          if (bol->in(1)->is_Cmp()) {
+            // If condition is invariant and not a loop exit,
+            // then found reason to unswitch.
+            if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {
+              unswitch_iff = iff;
+            }
+          }
+        }
+      }
+    }
+    n = n_dom;
+  }
+  return unswitch_iff;
+}
+
+//------------------------------do_unswitching-----------------------------
+// Clone loop with an invariant test (that does not exit) and
+// insert a clone of the test that selects which version to
+// execute.
+void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) {
+
+  // Find first invariant test that doesn't exit the loop
+  LoopNode *head = loop->_head->as_Loop();
+
+  IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);
+  assert(unswitch_iff != NULL, "should be at least one");
+
+  // Need to revert back to normal loop
+  if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
+    head->as_CountedLoop()->set_normal_loop();
+  }
+
+  ProjNode* proj_true = create_slow_version_of_loop(loop, old_new);
+
+  assert(proj_true->is_IfTrue() && proj_true->unique_ctrl_out() == head, "by construction");
+
+  // Increment unswitch count
+  LoopNode* head_clone = old_new[head->_idx]->as_Loop();
+  int nct = head->unswitch_count() + 1;
+  head->set_unswitch_count(nct);
+  head_clone->set_unswitch_count(nct);
+
+  // Add test to new "if" outside of loop
+  IfNode* invar_iff   = proj_true->in(0)->as_If();
+  Node* invar_iff_c   = invar_iff->in(0);
+  BoolNode* bol       = unswitch_iff->in(1)->as_Bool();
+  invar_iff->set_req(1, bol);
+  invar_iff->_prob    = unswitch_iff->_prob;
+
+  ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();
+
+  // Hoist invariant casts out of each loop to the appropiate
+  // control projection.
+
+  Node_List worklist;
+
+  for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {
+    ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();
+    // Copy to a worklist for easier manipulation
+    for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
+      Node* use = proj->fast_out(j);
+      if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
+        worklist.push(use);
+      }
+    }
+    ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
+    while (worklist.size() > 0) {
+      Node* use = worklist.pop();
+      Node* nuse = use->clone();
+      nuse->set_req(0, invar_proj);
+      _igvn.hash_delete(use);
+      use->set_req(1, nuse);
+      _igvn._worklist.push(use);
+      register_new_node(nuse, invar_proj);
+      // Same for the clone
+      Node* use_clone = old_new[use->_idx];
+      _igvn.hash_delete(use_clone);
+      use_clone->set_req(1, nuse);
+      _igvn._worklist.push(use_clone);
+    }
+  }
+
+  // Hardwire the control paths in the loops into if(true) and if(false)
+  _igvn.hash_delete(unswitch_iff);
+  short_circuit_if(unswitch_iff, proj_true);
+  _igvn._worklist.push(unswitch_iff);
+
+  IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
+  _igvn.hash_delete(unswitch_iff_clone);
+  short_circuit_if(unswitch_iff_clone, proj_false);
+  _igvn._worklist.push(unswitch_iff_clone);
+
+  // Reoptimize loops
+  loop->record_for_igvn();
+  for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
+    Node *n = loop->_body[i];
+    Node *n_clone = old_new[n->_idx];
+    _igvn._worklist.push(n_clone);
+  }
+
+#ifndef PRODUCT
+  if (TraceLoopUnswitching) {
+    tty->print_cr("Loop unswitching orig: %d @ %d  new: %d @ %d",
+                  head->_idx,                unswitch_iff->_idx,
+                  old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);
+  }
+#endif
+
+  C->set_major_progress();
+}
+
+//-------------------------create_slow_version_of_loop------------------------
+// Create a slow version of the loop by cloning the loop
+// and inserting an if to select fast-slow versions.
+// Return control projection of the entry to the fast version.
+ProjNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
+                                                      Node_List &old_new) {
+  LoopNode* head  = loop->_head->as_Loop();
+  Node*     entry = head->in(LoopNode::EntryControl);
+  _igvn.hash_delete(entry);
+  _igvn._worklist.push(entry);
+  IdealLoopTree* outer_loop = loop->_parent;
+
+  Node *cont      = _igvn.intcon(1);
+  set_ctrl(cont, C->root());
+  Node* opq       = new (C, 2) Opaque1Node(cont);
+  register_node(opq, outer_loop, entry, dom_depth(entry));
+  Node *bol       = new (C, 2) Conv2BNode(opq);
+  register_node(bol, outer_loop, entry, dom_depth(entry));
+  IfNode* iff = new (C, 2) IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN);
+  register_node(iff, outer_loop, entry, dom_depth(entry));
+  ProjNode* iffast = new (C, 1) IfTrueNode(iff);
+  register_node(iffast, outer_loop, iff, dom_depth(iff));
+  ProjNode* ifslow = new (C, 1) IfFalseNode(iff);
+  register_node(ifslow, outer_loop, iff, dom_depth(iff));
+
+  // Clone the loop body.  The clone becomes the fast loop.  The
+  // original pre-header will (illegally) have 2 control users (old & new loops).
+  clone_loop(loop, old_new, dom_depth(head), iff);
+  assert(old_new[head->_idx]->is_Loop(), "" );
+
+  // Fast (true) control
+  _igvn.hash_delete(head);
+  head->set_req(LoopNode::EntryControl, iffast);
+  set_idom(head, iffast, dom_depth(head));
+  _igvn._worklist.push(head);
+
+  // Slow (false) control
+  LoopNode* slow_head = old_new[head->_idx]->as_Loop();
+  _igvn.hash_delete(slow_head);
+  slow_head->set_req(LoopNode::EntryControl, ifslow);
+  set_idom(slow_head, ifslow, dom_depth(slow_head));
+  _igvn._worklist.push(slow_head);
+
+  recompute_dom_depth();
+
+  return iffast;
+}