[turbofan] simplify gap ordering

test/unittests/compiler/move-optimizer-unittest.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/move-optimizer.h"
 #include "test/unittests/compiler/instruction-sequence-unittest.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 class MoveOptimizerTest : public InstructionSequenceTest {
  public:
   GapInstruction* LastGap() {
-    auto instruction = sequence()->instructions().back();
-    if (!instruction->IsGapMoves()) {
-      instruction = *(sequence()->instructions().rbegin() + 1);
-    }
-    return GapInstruction::cast(instruction);
+    return GapInstruction::cast(*(sequence()->instructions().rbegin() + 1));
   }
 
   void AddMove(GapInstruction* gap, TestOperand from, TestOperand to,
                GapInstruction::InnerPosition pos = GapInstruction::START) {
     auto parallel_move = gap->GetOrCreateParallelMove(pos, zone());
     parallel_move->AddMove(ConvertMoveArg(from), ConvertMoveArg(to), zone());
   }
 
   int NonRedundantSize(ParallelMove* move) {
     int i = 0;
@@ skipping 53 matching lines @@
         break;
     }
     CHECK(false);
     return nullptr;
   }
 };
 
 
 TEST_F(MoveOptimizerTest, RemovesRedundant) {
   StartBlock();
+  EmitNop();
   AddMove(LastGap(), Reg(0), Reg(1));
   EmitNop();
   AddMove(LastGap(), Reg(1), Reg(0));
-  EmitNop();
   EndBlock(Last());
 
   Optimize();
 
   auto gap = LastGap();
   auto move = gap->parallel_moves()[0];
   CHECK_EQ(1, NonRedundantSize(move));
   CHECK(Contains(move, Reg(0), Reg(1)));
 }
 
@@ skipping 17 matching lines @@
   move = gap->parallel_moves()[1];
   CHECK_EQ(3, NonRedundantSize(move));
   CHECK(Contains(move, Reg(0), Slot(0)));
   CHECK(Contains(move, Reg(0), Slot(1)));
   CHECK(Contains(move, Reg(0), Slot(2)));
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8