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8228772: C2 compilation fails due to unschedulable graph if DominatorSearchLimit is reached

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Ignore membar if the load is already control dependent on it.

Reviewed-by: neliasso, kvn
This commit is contained in:
Tobias Hartmann 2019-08-13 09:54:40 +02:00
parent 5225d254ee
commit f1763a5e86
2 changed files with 465 additions and 2 deletions
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17
src/hotspot/share/opto/gcm.cpp
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@ -663,6 +663,19 @@ Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {
// instead of control + memory.
if (mstore->ideal_Opcode() == Op_SafePoint)
continue;
// Check if the store is a membar on which the load is control dependent.
// Inserting an anti-dependency between that membar and the load would
// create a cycle that causes local scheduling to fail.
if (mstore->isa_MachMemBar()) {
Node* dom = load->find_exact_control(load->in(0));
while (dom != NULL && dom != dom->in(0) && dom != mstore) {
dom = dom->in(0);
}
if (dom == mstore) {
continue;
}
}
} else {
// Some raw memory, such as the load of "top" at an allocation,
// can be control dependent on the previous safepoint. See
@ -747,7 +760,7 @@ Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {
// Found a possibly-interfering store in the load's 'early' block.
// This means 'load' cannot sink at all in the dominator tree.
// Add an anti-dep edge, and squeeze 'load' into the highest block.
assert(store != load->in(0), "dependence cycle found");
assert(store != load->find_exact_control(load->in(0)), "dependence cycle found");
if (verify) {
assert(store->find_edge(load) != -1, "missing precedence edge");
} else {
@ -787,7 +800,7 @@ Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {
Block* store_block = get_block_for_node(store);
if (store_block == LCA) {
// add anti_dependence from store to load in its own block
assert(store != load->in(0), "dependence cycle found");
assert(store != load->find_exact_control(load->in(0)), "dependence cycle found");
if (verify) {
assert(store->find_edge(load) != -1, "missing precedence edge");
} else {