[turbofan] put gaps before instructions

src/compiler/instruction.cc

Index: src/compiler/instruction.cc
diff --git a/src/compiler/instruction.cc b/src/compiler/instruction.cc
index 3c617327f4614f972837aba787faa73820254081..fe9a8802ffb4236e03fc30d98ed8db74a502cbb4 100644
--- a/src/compiler/instruction.cc
+++ b/src/compiler/instruction.cc
@@ -280,7 +280,7 @@ std::ostream& operator<<(std::ostream& os,
 
   if (instr.IsGapMoves()) {
     const GapInstruction* gap = GapInstruction::cast(&instr);
-    os << (instr.IsBlockStart() ? " block-start" : "gap ");
+    os << "gap ";
     for (int i = GapInstruction::FIRST_INNER_POSITION;
          i <= GapInstruction::LAST_INNER_POSITION; i++) {
       os << "(";
@@ -291,6 +291,8 @@ std::ostream& operator<<(std::ostream& os,
       }
       os << ") ";
     }
+  } else if (instr.IsBlockStart()) {
+    os << "block-start";
   } else if (instr.IsSourcePosition()) {
     const SourcePositionInstruction* pos =
         SourcePositionInstruction::cast(&instr);
@@ -434,7 +436,7 @@ InstructionSequence::InstructionSequence(Zone* instruction_zone,
 }
 
 
-BlockStartInstruction* InstructionSequence::GetBlockStart(
+const BlockStartInstruction* InstructionSequence::GetBlockStart(
     BasicBlock::RpoNumber rpo) const {
   const InstructionBlock* block = InstructionBlockAt(rpo);
   return BlockStartInstruction::cast(InstructionAt(block->code_start()));
@@ -447,8 +449,7 @@ void InstructionSequence::StartBlock(BasicBlock::RpoNumber rpo) {
   int code_start = static_cast<int>(instructions_.size());
   block->set_code_start(code_start);
   block_starts_.push_back(code_start);
-  BlockStartInstruction* block_start = BlockStartInstruction::New(zone());
-  AddInstruction(block_start);
+  instructions_.push_back(BlockStartInstruction::New(zone()));
 }
 
 
@@ -461,12 +462,10 @@ void InstructionSequence::EndBlock(BasicBlock::RpoNumber rpo) {
 
 
 int InstructionSequence::AddInstruction(Instruction* instr) {
-  // TODO(titzer): the order of these gaps is a holdover from Lithium.
   GapInstruction* gap = GapInstruction::New(zone());
-  if (instr->IsControl()) instructions_.push_back(gap);
+  instructions_.push_back(gap);
   int index = static_cast<int>(instructions_.size());
   instructions_.push_back(instr);
-  if (!instr->IsControl()) instructions_.push_back(gap);
   if (instr->NeedsPointerMap()) {
     DCHECK(instr->pointer_map() == NULL);
     PointerMap* pointer_map = new (zone()) PointerMap(zone());