1.1 --- a/src/share/vm/opto/loopTransform.cpp Sat Mar 26 08:31:45 2011 -0700
1.2 +++ b/src/share/vm/opto/loopTransform.cpp Sun Mar 27 00:00:14 2011 -0700
1.3 @@ -1608,15 +1608,7 @@
1.4 return false; // Malformed loop
1.5 if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
1.6 return false; // Infinite loop
1.7 -#ifndef PRODUCT
1.8 - if (PrintOpto) {
1.9 - tty->print("Removing empty loop");
1.10 - this->dump_head();
1.11 - } else if (TraceLoopOpts) {
1.12 - tty->print("Empty ");
1.13 - this->dump_head();
1.14 - }
1.15 -#endif
1.16 +
1.17 #ifdef ASSERT
1.18 // Ensure only one phi which is the iv.
1.19 Node* iv = NULL;
1.20 @@ -1629,6 +1621,43 @@
1.21 }
1.22 assert(iv == cl->phi(), "Wrong phi" );
1.23 #endif
1.24 +
1.25 + // main and post loops have explicitly created zero trip guard
1.26 + bool needs_guard = !cl->is_main_loop() && !cl->is_post_loop();
1.27 + if (needs_guard) {
1.28 + // Check for an obvious zero trip guard.
1.29 + Node* inctrl = cl->in(LoopNode::EntryControl);
1.30 + if (inctrl->Opcode() == Op_IfTrue) {
1.31 + // The test should look like just the backedge of a CountedLoop
1.32 + Node* iff = inctrl->in(0);
1.33 + if (iff->is_If()) {
1.34 + Node* bol = iff->in(1);
1.35 + if (bol->is_Bool() && bol->as_Bool()->_test._test == cl->loopexit()->test_trip()) {
1.36 + Node* cmp = bol->in(1);
1.37 + if (cmp->is_Cmp() && cmp->in(1) == cl->init_trip() && cmp->in(2) == cl->limit()) {
1.38 + needs_guard = false;
1.39 + }
1.40 + }
1.41 + }
1.42 + }
1.43 + }
1.44 +
1.45 +#ifndef PRODUCT
1.46 + if (PrintOpto) {
1.47 + tty->print("Removing empty loop with%s zero trip guard", needs_guard ? "out" : "");
1.48 + this->dump_head();
1.49 + } else if (TraceLoopOpts) {
1.50 + tty->print("Empty with%s zero trip guard ", needs_guard ? "out" : "");
1.51 + this->dump_head();
1.52 + }
1.53 +#endif
1.54 +
1.55 + if (needs_guard) {
1.56 + // Peel the loop to ensure there's a zero trip guard
1.57 + Node_List old_new;
1.58 + phase->do_peeling(this, old_new);
1.59 + }
1.60 +
1.61 // Replace the phi at loop head with the final value of the last
1.62 // iteration. Then the CountedLoopEnd will collapse (backedge never
1.63 // taken) and all loop-invariant uses of the exit values will be correct.
