Add canonicalize optimization for branches.

runtime/vm/intermediate_language.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/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
 #include "vm/flow_graph_optimizer.h"
 #include "vm/locations.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/os.h"
 #include "vm/scopes.h"
 #include "vm/stub_code.h"
 #include "vm/symbols.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, new_identity_spec, true,
     "Use new identity check rules for numbers.");
 DEFINE_FLAG(bool, propagate_ic_data, true,
     "Propagate IC data from unoptimized to optimized IC calls.");
 DECLARE_FLAG(bool, enable_type_checks);
 DECLARE_FLAG(int, max_polymorphic_checks);
+DECLARE_FLAG(bool, trace_optimization);
 
 Definition::Definition()
     : range_(NULL),
       temp_index_(-1),
       ssa_temp_index_(-1),
       propagated_type_(AbstractType::Handle()),
       propagated_cid_(kIllegalCid),
       input_use_list_(NULL),
       env_use_list_(NULL),
       use_kind_(kValue),  // Phis and parameters rely on this default.
@@ skipping 1640 matching lines @@
     // It is ok to insert instructions before the current during
     // forward iteration.
     optimizer->InsertBefore(this, null_constant, NULL, Definition::kValue);
     instantiator_type_arguments()->RemoveFromInputUseList();
     instantiator_type_arguments()->set_definition(null_constant);
     instantiator_type_arguments()->AddToInputUseList();
   }
   return this;
 }
 
+
+Instruction* BranchInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
+  if (comparison()->IsStrictCompare()) {
+    Definition* replacement = comparison()->Canonicalize(optimizer);

[Kevin Millikin (Google), 2013/01/10 10:35:00]

It might be simpler with an early return, and I like to avoid calling both IsXXX
and AsXXX on the same instruction.  Also, the code should be safe if
comparison()->Canonicalize() returns NULL (or at least assert that it doesn't). 
What do you think of:

Definition* replacement = comparison()->Canonicalize(optimizer);
if ((replacement == comparision()) || (replacement == NULL)) return this;
ComparisonInstr* comp = replacement->AsComparison();
if (comp == NULL) return this;

// Replace the comparison if the replacement is only used in this branch.
if ((comp->...) && ... && ...) ...

[Florian Schneider, 2013/01/10 13:18:41]

Done.

+    if ((replacement != comparison()) &&
+        replacement->IsComparison()) {
+      ComparisonInstr* comp = replacement->AsComparison();
+      if ((comp->input_use_list()->instruction() == this) &&
+          (comp->input_use_list()->next_use() == NULL) &&
+          (comp->env_use_list() == NULL)) {
+        // Replace the comparison if the replacement is used at this branch,
+        // and has exactly one use.
+        comp->RemoveFromGraph();
+        ReplaceWith(comp, NULL /* ignored */);

[Kevin Millikin (Google), 2013/01/10 10:35:00]

You should expand the comment about NULL so the reader doesn't have to look at
ReplaceWith.

// It's safe to pass a NULL instruction iterator because we're sure that the
replacement is not the canonicalization iterator's current instruction.

[Florian Schneider, 2013/01/10 13:18:41]

Done.

+        for (intptr_t i = 0; i < comp->InputCount(); ++i) {
+          Value* operand = comp->InputAt(i);
+          operand->set_instruction(this);
+        }
+        if (FLAG_trace_optimization) {
+          OS::Print("Merging comparison v%"Pd"\n", comp->ssa_temp_index());
+        }
+      }
+    }
+  }
+  return this;
+}
+
+
 Definition* StrictCompareInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
   if (!right()->BindsToConstant()) return this;
   const Object& right_constant = right()->BoundConstant();
   Definition* left_defn = left()->definition();
   // TODO(fschneider): Handle other cases: e === false and e !== true/false.
   // Handles e === true.
   if ((kind() == Token::kEQ_STRICT) &&
       (right_constant.raw() == Bool::True().raw()) &&
       (left()->ResultCid() == kBoolCid)) {
     // Return left subexpression as the replacement for this instruction.
@@ skipping 1218 matching lines @@
     default:
       UNREACHABLE();
       return -1;
   }
 }
 
 
 #undef __
 
 }  // namespace dart