Optimize functions containing try-catch.

runtime/vm/flow_graph.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flow_graph.h"
 
 #include "vm/bit_vector.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/intermediate_language.h"
 #include "vm/longjump.h"
 #include "vm/growable_array.h"
 
 namespace dart {
 
 DECLARE_FLAG(bool, trace_optimization);
 DECLARE_FLAG(bool, verify_compiler);
 
+#if defined(TARGET_ARCH_ARM) || defined(TARGET_ARCH_MIPS)
+DEFINE_FLAG(bool, optimize_try_catch, false, "Optimization of try-catch");
+#else
+DEFINE_FLAG(bool, optimize_try_catch, true, "Optimization of try-catch");
+#endif
+
 FlowGraph::FlowGraph(const FlowGraphBuilder& builder,
                      GraphEntryInstr* graph_entry,
                      intptr_t max_block_id)
   : parent_(),
     current_ssa_temp_index_(0),
     max_block_id_(max_block_id),
     parsed_function_(builder.parsed_function()),
     num_copied_params_(builder.num_copied_params()),
     num_non_copied_params_(builder.num_non_copied_params()),
     num_stack_locals_(builder.num_stack_locals()),
@@ skipping 293 matching lines @@
   // have new assigned values flowing out of that block.
   const GrowableArray<BitVector*>& ComputeAssignedVars() {
     // We can't directly return kill_ because it uses postorder numbering while
     // SSA construction uses preorder numbering internally.
     // We have to permute postorder into preorder.
     assigned_vars_.Clear();
 
     const intptr_t block_count = flow_graph_->preorder().length();
     for (intptr_t i = 0; i < block_count; i++) {
       BlockEntryInstr* block = flow_graph_->preorder()[i];
+      // All locals are assigned inside a try{} block.
+      // This is a safe approximation and workaround to force insertion of
+      // phis for stores that appear non-live because of the way catch-blocks
+      // are connected to the graph: They normally are dominated by the
+      // try-entry, but are direct successors of the graph entry in our flow
+      // graph.
+      // TODO(fschneider): Improve this approximation by better modeling the
+      // actual data flow to reduce the number of redundant phis.
       BitVector* kill = GetKillSet(block);
-      kill->Intersect(GetLiveOutSet(block));
+      if (block->InsideTryBlock()) {
+        kill->SetAll();
+      } else {
+        kill->Intersect(GetLiveOutSet(block));
+      }
       assigned_vars_.Add(kill);
     }
 
     return assigned_vars_;
   }
 
   // Returns true if the value set by the given store reaches any load from the
   // same local variable.
   bool IsStoreAlive(BlockEntryInstr* block, StoreLocalInstr* store) {
     if (store->is_dead()) {
@@ skipping 28 matching lines @@
   const intptr_t block_count = postorder_.length();
 
   BitVector* last_loads = new BitVector(variable_count_);
   for (intptr_t i = 0; i < block_count; i++) {
     BlockEntryInstr* block = postorder_[i];
 
     BitVector* kill = kill_[i];
     BitVector* live_in = live_in_[i];
     last_loads->Clear();
 
+    // There is an implicit use (load-local) of every local variable at each
+    // call inside a try{} block and every call has an implicit control-flow
+    // to the catch entry. As an approximation we mark all locals as live
+    // inside try{}.
+    // TODO(fschneider): Improve this approximation, since not all local
+    // variable stores actually reach a call.
+    if (block->InsideTryBlock()) {
+      live_in->SetAll();
+      continue;
+    }
+
     // Iterate backwards starting at the last instruction.
     for (BackwardInstructionIterator it(block); !it.Done(); it.Advance()) {
       Instruction* current = it.Current();
 
       LoadLocalInstr* load = current->AsLoadLocal();
       if (load != NULL) {
         const intptr_t index = load->local().BitIndexIn(num_non_copied_params_);
         live_in->Add(index);
         if (!last_loads->Contains(index)) {
           last_loads->Add(index);
@@ skipping 219 matching lines @@
         }
       }
     }
   }
 }
 
 
 void FlowGraph::Rename(GrowableArray<PhiInstr*>* live_phis,
                        VariableLivenessAnalysis* variable_liveness,
                        ZoneGrowableArray<Definition*>* inlining_parameters) {
-  // TODO(fschneider): Support catch-entry.
-  if (graph_entry_->SuccessorCount() > 1) {
+  if (!FLAG_optimize_try_catch && (graph_entry_->SuccessorCount() > 1)) {
     Bailout("Catch-entry support in SSA.");
   }
 
   // Initial renaming environment.
   GrowableArray<Definition*> env(variable_count());
 
   // Add global constants to the initial definitions.
   constant_null_ = GetConstant(Object::ZoneHandle());
 
   // Add parameters to the initial definitions and renaming environment.
@@ skipping 14 matching lines @@
       AddToInitialDefinitions(param);
       env.Add(param);
     }
   }
 
   // Initialize all locals with #null in the renaming environment.
   for (intptr_t i = parameter_count(); i < variable_count(); ++i) {
     env.Add(constant_null());
   }
 
-  BlockEntryInstr* normal_entry = graph_entry_->SuccessorAt(0);
-  ASSERT(normal_entry != NULL);  // Must have entry.
-  RenameRecursive(normal_entry, &env, live_phis, variable_liveness);
+  if (graph_entry_->SuccessorCount() > 1) {
+    // Functions with try-catch have a fixed area of stack slots reserved
+    // so that all local variables are stored at a known location when
+    // on entry to the catch.
+    graph_entry_->set_fixed_slot_count(
+        num_stack_locals() + num_copied_params());
+  }
+  RenameRecursive(graph_entry_, &env, live_phis, variable_liveness);
 }
 
 
 void FlowGraph::AttachEnvironment(Instruction* instr,
                                   GrowableArray<Definition*>* env) {
   Environment* deopt_env =
       Environment::From(*env,
                         num_non_copied_params_,
                         parsed_function_.function());
   instr->SetEnvironment(deopt_env);
@@ skipping 13 matching lines @@
                                 VariableLivenessAnalysis* variable_liveness) {
   // 1. Process phis first.
   if (block_entry->IsJoinEntry()) {
     JoinEntryInstr* join = block_entry->AsJoinEntry();
     if (join->phis() != NULL) {
       for (intptr_t i = 0; i < join->phis()->length(); ++i) {
         PhiInstr* phi = (*join->phis())[i];
         if (phi != NULL) {
           (*env)[i] = phi;
           phi->set_ssa_temp_index(alloc_ssa_temp_index());  // New SSA temp.
+          if (block_entry->InsideTryBlock()) {
+            // This is a safe approximation.  Inside try{} all locals are
+            // used at every call implicitly, so we mark all phis as live
+            // from the start.
+            // TODO(fschneider): Improve this approximation to eliminate
+            // more redundant phis.
+            phi->mark_alive();
+            live_phis->Add(phi);
+          }
         }
       }
     }
+  } else if (block_entry->IsCatchBlockEntry()) {
+    // Add real definitions for all locals and parameters.
+    for (intptr_t i = 0; i < env->length(); ++i) {
+      ParameterInstr* param = new ParameterInstr(i, block_entry);
+      param->set_ssa_temp_index(alloc_ssa_temp_index());  // New SSA temp.
+      (*env)[i] = param;
+      block_entry->AsCatchBlockEntry()->initial_definitions()->Add(param);
+    }
   }
 
   // Attach environment to the block entry.
   AttachEnvironment(block_entry, env);
 
   // 2. Process normal instructions.
   for (ForwardInstructionIterator it(block_entry); !it.Done(); it.Advance()) {
     Instruction* current = it.Current();
 
     // Attach current environment to the instructions that need it.
@@ skipping 352 matching lines @@
 }
 
 
 bool BlockEffects::IsSideEffectFreePath(BlockEntryInstr* from,
                                         BlockEntryInstr* to) const {
   return available_at_[to->postorder_number()]->Contains(
       from->postorder_number());
 }
 
 }  // namespace dart