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7024475: loop doesn't terminate when compiled

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Reviewed-by: kvn
This commit is contained in:
Tom Rodriguez 2011-03-27 00:00:14 -07:00
parent 360a7be9a7
commit 5387ee459e
8 changed files with 185 additions and 37 deletions
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47
hotspot/src/share/vm/opto/loopTransform.cpp
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@ -1608,15 +1608,7 @@ bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {
return false; // Malformed loop
if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
return false; // Infinite loop
#ifndef PRODUCT
if (PrintOpto) {
tty->print("Removing empty loop");
this->dump_head();
} else if (TraceLoopOpts) {
tty->print("Empty ");
this->dump_head();
}
#endif
#ifdef ASSERT
// Ensure only one phi which is the iv.
Node* iv = NULL;
@ -1629,6 +1621,43 @@ bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {
}
assert(iv == cl->phi(), "Wrong phi" );
#endif
// main and post loops have explicitly created zero trip guard
bool needs_guard = !cl->is_main_loop() && !cl->is_post_loop();
if (needs_guard) {
// Check for an obvious zero trip guard.
Node* inctrl = cl->in(LoopNode::EntryControl);
if (inctrl->Opcode() == Op_IfTrue) {
// The test should look like just the backedge of a CountedLoop
Node* iff = inctrl->in(0);
if (iff->is_If()) {
Node* bol = iff->in(1);
if (bol->is_Bool() && bol->as_Bool()->_test._test == cl->loopexit()->test_trip()) {
Node* cmp = bol->in(1);
if (cmp->is_Cmp() && cmp->in(1) == cl->init_trip() && cmp->in(2) == cl->limit()) {
needs_guard = false;
}
}
}
}
}
#ifndef PRODUCT
if (PrintOpto) {
tty->print("Removing empty loop with%s zero trip guard", needs_guard ? "out" : "");
this->dump_head();
} else if (TraceLoopOpts) {
tty->print("Empty with%s zero trip guard ", needs_guard ? "out" : "");
this->dump_head();
}
#endif
if (needs_guard) {
// Peel the loop to ensure there's a zero trip guard
Node_List old_new;
phase->do_peeling(this, old_new);
}
// Replace the phi at loop head with the final value of the last
// iteration. Then the CountedLoopEnd will collapse (backedge never
// taken) and all loop-invariant uses of the exit values will be correct.