optimizing: add block-scoped constructor fence merging pass
Introduce a new "Constructor Fence Redundancy Elimination" pass.
The pass currently performs local optimization only, i.e. within instructions
in the same basic block.
All constructor fences preceding a publish (e.g. store, invoke) get
merged into one instruction.
==============
OptStat#ConstructorFenceGeneratedNew: 43825
OptStat#ConstructorFenceGeneratedFinal: 17631 <+++
OptStat#ConstructorFenceRemovedLSE: 164
OptStat#ConstructorFenceRemovedPFRA: 9391
OptStat#ConstructorFenceRemovedCFRE: 16133 <---
Removes ~91.5% of the 'final' constructor fences in RitzBenchmark:
(We do not distinguish the exact reason that a fence was created, so
it's possible some "new" fences were also removed.)
==============
Test: art/test/run-test --host --optimizing 476-checker-ctor-fence-redun-elim
Bug: 36656456
Change-Id: I8020217b448ad96ce9b7640aa312ae784690ad99
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 8644f67..e34d4a2 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -1271,18 +1271,59 @@
return remove_count;
}
-HInstruction* HConstructorFence::GetAssociatedAllocation() {
+void HConstructorFence::Merge(HConstructorFence* other) {
+ // Do not delete yourself from the graph.
+ DCHECK(this != other);
+ // Don't try to merge with an instruction not associated with a block.
+ DCHECK(other->GetBlock() != nullptr);
+ // A constructor fence's return type is "kPrimVoid"
+ // and therefore it cannot have any environment uses.
+ DCHECK(!other->HasEnvironmentUses());
+
+ auto has_input = [](HInstruction* haystack, HInstruction* needle) {
+ // Check if `haystack` has `needle` as any of its inputs.
+ for (size_t input_count = 0; input_count < haystack->InputCount(); ++input_count) {
+ if (haystack->InputAt(input_count) == needle) {
+ return true;
+ }
+ }
+ return false;
+ };
+
+ // Add any inputs from `other` into `this` if it wasn't already an input.
+ for (size_t input_count = 0; input_count < other->InputCount(); ++input_count) {
+ HInstruction* other_input = other->InputAt(input_count);
+ if (!has_input(this, other_input)) {
+ AddInput(other_input);
+ }
+ }
+
+ other->GetBlock()->RemoveInstruction(other);
+}
+
+HInstruction* HConstructorFence::GetAssociatedAllocation(bool ignore_inputs) {
HInstruction* new_instance_inst = GetPrevious();
// Check if the immediately preceding instruction is a new-instance/new-array.
// Otherwise this fence is for protecting final fields.
if (new_instance_inst != nullptr &&
(new_instance_inst->IsNewInstance() || new_instance_inst->IsNewArray())) {
- // TODO: Need to update this code to handle multiple inputs.
- DCHECK_EQ(InputCount(), 1u);
- return new_instance_inst;
- } else {
- return nullptr;
+ if (ignore_inputs) {
+ // If inputs are ignored, simply check if the predecessor is
+ // *any* HNewInstance/HNewArray.
+ //
+ // Inputs are normally only ignored for prepare_for_register_allocation,
+ // at which point *any* prior HNewInstance/Array can be considered
+ // associated.
+ return new_instance_inst;
+ } else {
+ // Normal case: There must be exactly 1 input and the previous instruction
+ // must be that input.
+ if (InputCount() == 1u && InputAt(0) == new_instance_inst) {
+ return new_instance_inst;
+ }
+ }
}
+ return nullptr;
}
#define DEFINE_ACCEPT(name, super) \