[turbofan] smash GapInstruction into Instruction

src/compiler/jump-threading.cc

Index: src/compiler/jump-threading.cc
diff --git a/src/compiler/jump-threading.cc b/src/compiler/jump-threading.cc
index e5b4595960d4ec2db1086ebe6d715f876335087d..96fb5db532400b8569632b09ab71b5a6919bb90d 100644
--- a/src/compiler/jump-threading.cc
+++ b/src/compiler/jump-threading.cc
@@ -76,10 +76,10 @@ bool JumpThreading::ComputeForwarding(Zone* local_zone,
       RpoNumber fw = block->rpo_number();
       for (int i = block->code_start(); i < block->code_end(); ++i) {
         Instruction* instr = code->InstructionAt(i);
-        if (instr->IsGapMoves() && GapInstruction::cast(instr)->IsRedundant()) {
-          // skip redundant gap moves.
-          TRACE("  nop gap\n");
-          continue;
+        if (!instr->AreMovesRedundant()) {
+          // can't skip instructions with non redundant moves.
+          TRACE("  parallel move\n");
+          fallthru = false;
         } else if (instr->IsSourcePosition()) {
           // skip source positions.
           TRACE("  src pos\n");