ART: Update DCE to work with try/catch
Dead block elimination was previously disabled because it needed
to be updated. With this patch, try/catch blocks can be removed
as a result of a dead if/switch branch.
Change-Id: I3261060bf24fd5fe7bb0f989247f0ef62ec5fd7b
diff --git a/compiler/optimizing/dead_code_elimination.cc b/compiler/optimizing/dead_code_elimination.cc
index 9754043..02e5dab 100644
--- a/compiler/optimizing/dead_code_elimination.cc
+++ b/compiler/optimizing/dead_code_elimination.cc
@@ -123,20 +123,21 @@
}
// If we removed at least one block, we need to recompute the full
- // dominator tree.
+ // dominator tree and try block membership.
if (removed_one_or_more_blocks) {
graph_->ClearDominanceInformation();
graph_->ComputeDominanceInformation();
+ graph_->ComputeTryBlockInformation();
}
// Connect successive blocks created by dead branches. Order does not matter.
for (HReversePostOrderIterator it(*graph_); !it.Done();) {
HBasicBlock* block = it.Current();
- if (block->IsEntryBlock() || block->GetSuccessors().size() != 1u) {
+ if (block->IsEntryBlock() || !block->GetLastInstruction()->IsGoto()) {
it.Advance();
continue;
}
- HBasicBlock* successor = block->GetSuccessors()[0];
+ HBasicBlock* successor = block->GetSingleSuccessor();
if (successor->IsExitBlock() || successor->GetPredecessors().size() != 1u) {
it.Advance();
continue;
@@ -176,10 +177,7 @@
}
void HDeadCodeElimination::Run() {
- if (!graph_->HasTryCatch()) {
- // TODO: Update dead block elimination and enable for try/catch.
- RemoveDeadBlocks();
- }
+ RemoveDeadBlocks();
SsaRedundantPhiElimination(graph_).Run();
RemoveDeadInstructions();
}
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 68fb0ac..4d79b55 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -366,7 +366,11 @@
HBasicBlock* first_predecessor = block->GetPredecessors()[0];
DCHECK(!block->IsLoopHeader() || !block->GetLoopInformation()->IsBackEdge(*first_predecessor));
const HTryBoundary* try_entry = first_predecessor->ComputeTryEntryOfSuccessors();
- if (try_entry != nullptr) {
+ if (try_entry != nullptr &&
+ (block->GetTryCatchInformation() == nullptr ||
+ try_entry != &block->GetTryCatchInformation()->GetTryEntry())) {
+ // We are either setting try block membership for the first time or it
+ // has changed.
block->SetTryCatchInformation(new (arena_) TryCatchInformation(*try_entry));
}
}
@@ -1372,13 +1376,30 @@
// instructions.
for (HBasicBlock* predecessor : predecessors_) {
HInstruction* last_instruction = predecessor->GetLastInstruction();
+ if (last_instruction->IsTryBoundary() && !IsCatchBlock()) {
+ // This block is the only normal-flow successor of the TryBoundary which
+ // makes `predecessor` dead. Since DCE removes blocks in post order,
+ // exception handlers of this TryBoundary were already visited and any
+ // remaining handlers therefore must be live. We remove `predecessor` from
+ // their list of predecessors.
+ DCHECK_EQ(last_instruction->AsTryBoundary()->GetNormalFlowSuccessor(), this);
+ while (predecessor->GetSuccessors().size() > 1) {
+ HBasicBlock* handler = predecessor->GetSuccessors()[1];
+ DCHECK(handler->IsCatchBlock());
+ predecessor->RemoveSuccessor(handler);
+ handler->RemovePredecessor(predecessor);
+ }
+ }
+
predecessor->RemoveSuccessor(this);
uint32_t num_pred_successors = predecessor->GetSuccessors().size();
if (num_pred_successors == 1u) {
// If we have one successor after removing one, then we must have
- // had an HIf or HPackedSwitch, as they have more than one successor.
- // Replace those with a HGoto.
- DCHECK(last_instruction->IsIf() || last_instruction->IsPackedSwitch());
+ // had an HIf, HPackedSwitch or HTryBoundary, as they have more than one
+ // successor. Replace those with a HGoto.
+ DCHECK(last_instruction->IsIf() ||
+ last_instruction->IsPackedSwitch() ||
+ (last_instruction->IsTryBoundary() && IsCatchBlock()));
predecessor->RemoveInstruction(last_instruction);
predecessor->AddInstruction(new (graph_->GetArena()) HGoto(last_instruction->GetDexPc()));
} else if (num_pred_successors == 0u) {
@@ -1387,10 +1408,12 @@
// SSAChecker fails unless it is not removed during the pass too.
predecessor->RemoveInstruction(last_instruction);
} else {
- // There are multiple successors left. This must come from a HPackedSwitch
- // and we are in the middle of removing the HPackedSwitch. Like above, leave
- // this alone, and the SSAChecker will fail if it is not removed as well.
- DCHECK(last_instruction->IsPackedSwitch());
+ // There are multiple successors left. The removed block might be a successor
+ // of a PackedSwitch which will be completely removed (perhaps replaced with
+ // a Goto), or we are deleting a catch block from a TryBoundary. In either
+ // case, leave `last_instruction` as is for now.
+ DCHECK(last_instruction->IsPackedSwitch() ||
+ (last_instruction->IsTryBoundary() && IsCatchBlock()));
}
}
predecessors_.clear();