Add a backward instruction iterator and use it in the liveness analysis.

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_builder.h"
 #include "vm/flow_graph_compiler.h"
@@ skipping 63 matching lines @@
 #undef DEFINE_ACCEPT
 
 
 void ForwardInstructionIterator::RemoveCurrentFromGraph() {
   ASSERT(!current_->IsBlockEntry());
   ASSERT(!current_->IsBranch());
   ASSERT(!current_->IsThrow());
   ASSERT(!current_->IsReturn());
   ASSERT(!current_->IsReThrow());
   ASSERT(current_->previous() != NULL);
+  ASSERT(current_ != block_entry_->last_instruction());
   Instruction* prev = current_->previous();
   Instruction* next = current_->next();
+  ASSERT(next != NULL);
+  ASSERT(!next->IsBlockEntry());
   prev->set_next(next);
-  ASSERT(next != NULL);
-  if (current_ != block_entry_->last_instruction()) {
-    ASSERT(!next->IsBlockEntry());
-    next->set_previous(prev);
-  } else {
-    ASSERT(current_->IsBind());
-    // Removing the last instruction of a block.
-    // Update last_instruction of the current basic block.
-    block_entry_->set_last_instruction(prev);
-  }
+  next->set_previous(prev);
   // Reset successor and previous instruction to indicate
   // that the instruction is removed from the graph.
   current_->set_previous(NULL);
   current_->set_next(NULL);
   current_ = prev;
 }
 
 
 // True iff. the v2 is above v1 on stack, or one of them is constant.
 static bool VerifyValues(Value* v1, Value* v2) {
@@ skipping 1206 matching lines @@
   const ExternalLabel label(closure_function.ToCString(), stub.EntryPoint());
   compiler->GenerateCall(token_pos(), try_index(), &label,
                          PcDescriptors::kOther);
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 
 #undef __
 
 }  // namespace dart