[turbofan] only use two gaps

src/compiler/instruction.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/instruction.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 63 matching lines @@
 
 
 bool ParallelMove::IsRedundant() const {
   for (int i = 0; i < move_operands_.length(); ++i) {
     if (!move_operands_[i].IsRedundant()) return false;
   }
   return true;
 }
 
 
+MoveOperands* ParallelMove::PrepareInsertAfter(MoveOperands* move) const {
+  auto move_ops = move_operands();
+  MoveOperands* replacement = nullptr;
+  MoveOperands* to_eliminate = nullptr;
+  for (auto curr = move_ops->begin(); curr != move_ops->end(); ++curr) {
+    if (curr->IsEliminated()) continue;
+    if (curr->destination()->Equals(move->source())) {
+      DCHECK(!replacement);
+      replacement = curr;
+      if (to_eliminate != nullptr) break;
+    } else if (curr->destination()->Equals(move->destination())) {
+      DCHECK(!to_eliminate);
+      to_eliminate = curr;
+      if (replacement != nullptr) break;
+    }
+  }
+  DCHECK(!(replacement == to_eliminate && replacement != nullptr));

[Benedikt Meurer, 2015/02/24 10:41:45]

DCHECK_IMPLIES? :-)

+  if (replacement != nullptr) move->set_source(replacement->source());
+  return to_eliminate;
+}
+
+
 Instruction::Instruction(InstructionCode opcode)
     : opcode_(opcode),
       bit_field_(OutputCountField::encode(0) | InputCountField::encode(0) |
                  TempCountField::encode(0) | IsCallField::encode(false) |
                  IsControlField::encode(false)),
       pointer_map_(NULL) {}
 
 
 Instruction::Instruction(InstructionCode opcode, size_t output_count,
                          InstructionOperand* outputs, size_t input_count,
@@ skipping 613 matching lines @@
       os << " B" << succ_block->id();
     }
     os << "\n";
   }
   return os;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8