Implement a branch optimization pass.

runtime/vm/intermediate_language.cc

 // Copyright (c) 2013, 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"
@@ skipping 479 matching lines @@
     Value* prev = previous_use();
     prev->set_next_use(next);
     if (next != NULL) next->set_previous_use(prev);
   }
 
   set_previous_use(NULL);
   set_next_use(NULL);
 }
 
 
+bool Definition::HasOnlyUse(Value* use) const {
+  if (((input_use_list() == use) && (env_use_list() == NULL)) ||
+      ((input_use_list() == NULL) && (env_use_list() == use))) {
+    return (use->next_use() == NULL);
+  }
+  return false;
+}
+
+
 void Definition::ReplaceUsesWith(Definition* other) {
   ASSERT(other != NULL);
   ASSERT(this != other);
 
   Value* current = NULL;
   Value* next = input_use_list();
   if (next != NULL) {
     // Change all the definitions.
     while (next != NULL) {
       current = next;
@@ skipping 646 matching lines @@
     case kUint64ArrayCid:
     case kFloat32ArrayCid:
     case kFloat64ArrayCid:
       return true;
     default:
       return false;
   }
 }
 
 
+Definition* ConstantInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
+  return HasUses() ? this : NULL;

[Vyacheslav Egorov (Google), 2013/03/06 16:44:22]

I'd really like to see a more generic dead code elimination pass.

[Kevin Millikin (Google), 2013/03/08 10:38:10]

Me too, but this doesn't really seem like an abuse of Canonicalize to me.

+}
+
+
 Definition* LoadFieldInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
   if (!IsImmutableLengthLoad()) return this;
 
   // For fixed length arrays if the array is the result of a known constructor
   // call we can replace the length load with the length argument passed to
   // the constructor.
   StaticCallInstr* call = value()->definition()->AsStaticCall();
   if ((call != NULL) &&
       call->is_known_list_constructor() &&
       IsFixedLengthArrayCid(call->Type()->ToCid())) {
@@ skipping 1096 matching lines @@
     default:
       UNREACHABLE();
   }
   return kPowRuntimeEntry;
 }
 
 
 #undef __
 
 }  // namespace dart