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8263075: C2: simplify anti-dependence check in PhaseCFG::implicit_null_check()

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Reviewed-by: kvn, thartmann, rcastanedalo
This commit is contained in:
Brian J. Stafford 2022-05-25 17:28:27 +00:00 committed by Vladimir Kozlov
parent 0b3d409540
commit c6743489d2
1 changed files with 21 additions and 19 deletions

40
src/hotspot/share/opto/lcm.cpp

@ -326,25 +326,27 @@ void PhaseCFG::implicit_null_check(Block* block, Node *proj, Node *val, int allo
Block *mb = get_block_for_node(mach);
// Hoisting stores requires more checks for the anti-dependence case.
// Give up hoisting if we have to move the store past any load.
if( was_store ) {
Block *b = mb; // Start searching here for a local load
// mach use (faulting) trying to hoist
// n might be blocker to hoisting
while( b != block ) {
uint k;
for( k = 1; k < b->number_of_nodes(); k++ ) {
Node *n = b->get_node(k);
if( n->needs_anti_dependence_check() &&
n->in(LoadNode::Memory) == mach->in(StoreNode::Memory) )
break; // Found anti-dependent load
}
if( k < b->number_of_nodes() )
break; // Found anti-dependent load
// Make sure control does not do a merge (would have to check allpaths)
if( b->num_preds() != 2 ) break;
b = get_block_for_node(b->pred(1)); // Move up to predecessor block
}
if( b != block ) continue;
if (was_store) {
// Make sure control does not do a merge (would have to check allpaths)
if (mb->num_preds() != 2) {
continue;
}
// mach is a store, hence block is the immediate dominator of mb.
// Due to the null-check shape of block (where its successors cannot re-join),
// block must be the direct predecessor of mb.
assert(get_block_for_node(mb->pred(1)) == block, "Unexpected predecessor block");
uint k;
uint num_nodes = mb->number_of_nodes();
for (k = 1; k < num_nodes; k++) {
Node *n = mb->get_node(k);
if (n->needs_anti_dependence_check() &&
n->in(LoadNode::Memory) == mach->in(StoreNode::Memory)) {
break; // Found anti-dependent load
}
}
if (k < num_nodes) {
continue; // Found anti-dependent load
}
}
// Make sure this memory op is not already being used for a NullCheck