[turbofan] Skip printing of empty gap moves.

R=bmeurer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/812983002

Cr-Commit-Position: refs/heads/master@{#25878}

src/compiler/instruction.cc

@@ -287,16 +287,18 @@ std::ostream& operator<<(std::ostream& os,
 
   if (instr.IsGapMoves()) {
     const GapInstruction* gap = GapInstruction::cast(&instr);
-    os << "gap ";
-    for (int i = GapInstruction::FIRST_INNER_POSITION;
-         i <= GapInstruction::LAST_INNER_POSITION; i++) {
-      os << "(";
-      if (gap->parallel_moves_[i] != NULL) {
-        PrintableParallelMove ppm = {printable.register_configuration_,
-                                     gap->parallel_moves_[i]};
-        os << ppm;
+    if (!gap->IsRedundant()) {
+      os << "gap ";
+      for (int i = GapInstruction::FIRST_INNER_POSITION;
+           i <= GapInstruction::LAST_INNER_POSITION; i++) {
+        os << "(";
+        if (gap->parallel_moves_[i] != NULL) {
+          PrintableParallelMove ppm = {printable.register_configuration_,
+                                       gap->parallel_moves_[i]};
+          os << ppm;
+        }
+        os << ") ";
       }
-      os << ") ";
     }
   } else if (instr.IsSourcePosition()) {
     const SourcePositionInstruction* pos =