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8210152: Optimize integer divisible by power-of-2 check

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Integer conditional negation operation before zero check is eliminated

Reviewed-by: kvn, thartmann
This commit is contained in:
Pengfei Li 2018-09-25 14:16:33 +02:00 committed by Tobias Hartmann
parent f8ba78868d
commit dd4961b5aa
1 changed files with 31 additions and 0 deletions
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31
src/hotspot/share/opto/subnode.cpp
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@ -1522,6 +1522,37 @@ Node *BoolNode::Ideal(PhaseGVN *phase, bool can_reshape) {
return new BoolNode( ncmp, _test._test );
}
// Change "bool eq/ne (cmp (phi (X -X) 0))" into "bool eq/ne (cmp X 0)"
// since zero check of conditional negation of an integer is equal to
// zero check of the integer directly.
if ((_test._test == BoolTest::eq || _test._test == BoolTest::ne) &&
(cop == Op_CmpI) &&
(cmp2_type == TypeInt::ZERO) &&
(cmp1_op == Op_Phi)) {
// There should be a diamond phi with true path at index 1 or 2
PhiNode *phi = cmp1->as_Phi();
int idx_true = phi->is_diamond_phi();
if (idx_true != 0) {
// True input is in(idx_true) while false input is in(3 - idx_true)
Node *tin = phi->in(idx_true);
Node *fin = phi->in(3 - idx_true);
if ((tin->Opcode() == Op_SubI) &&
(phase->type(tin->in(1)) == TypeInt::ZERO) &&
(tin->in(2) == fin)) {
// Found conditional negation at true path, create a new CmpINode without that
Node *ncmp = phase->transform(new CmpINode(fin, cmp2));
return new BoolNode(ncmp, _test._test);
}
if ((fin->Opcode() == Op_SubI) &&
(phase->type(fin->in(1)) == TypeInt::ZERO) &&
(fin->in(2) == tin)) {
// Found conditional negation at false path, create a new CmpINode without that
Node *ncmp = phase->transform(new CmpINode(tin, cmp2));
return new BoolNode(ncmp, _test._test);
}
}
}
// Change (-A vs 0) into (A vs 0) by commuting the test. Disallow in the
// most general case because negating 0x80000000 does nothing. Needed for
// the CmpF3/SubI/CmpI idiom.