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8137049: Code quality: reducing an trivial integer loop does not produce an optimal code

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Canonicalized if shape not recognized by empty loop detection code

Reviewed-by: kvn, shade
This commit is contained in:
Roland Westrelin 2016-01-29 17:18:35 +01:00
parent 60a582e9be
commit 7fa54e38e6
1 changed files with 15 additions and 5 deletions
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20
hotspot/src/share/vm/opto/loopTransform.cpp
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@ -2404,15 +2404,25 @@ bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {
if (needs_guard) {
// Check for an obvious zero trip guard.
Node* inctrl = PhaseIdealLoop::skip_loop_predicates(cl->in(LoopNode::EntryControl));
if (inctrl->Opcode() == Op_IfTrue) {
if (inctrl->Opcode() == Op_IfTrue || inctrl->Opcode() == Op_IfFalse) {
bool maybe_swapped = (inctrl->Opcode() == Op_IfFalse);
// 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;
if (bol->is_Bool()) {
BoolTest test = bol->as_Bool()->_test;
if (maybe_swapped) {
test._test = test.commute();
test._test = test.negate();
}
if (test._test == cl->loopexit()->test_trip()) {
Node* cmp = bol->in(1);
int init_idx = maybe_swapped ? 2 : 1;
int limit_idx = maybe_swapped ? 1 : 2;
if (cmp->is_Cmp() && cmp->in(init_idx) == cl->init_trip() && cmp->in(limit_idx) == cl->limit()) {
needs_guard = false;
}
}
}
}