[turbofan][x64] Fix instruction selection for Word32Equal.

The InstructionSelector on x64 didn't properly implement
VisitWord32Equal via VisitWordCompareZero, and thus it didn't
properly combined useless Word32Equal comparisons with zero
(which we use to implement bit negation).

R=jarin@chromium.org
BUG=v8:5267

Review-Url: https://codereview.chromium.org/2662123004
Cr-Commit-Position: refs/heads/master@{#42841}

src/compiler/x64/instruction-selector-x64.cc

@@ -2071,12 +2071,8 @@ void VisitWordCompareZero(InstructionSelector* selector, Node* user,
         break;
       case IrOpcode::kInt32Sub:
         return VisitWordCompare(selector, value, kX64Cmp32, cont);
-      case IrOpcode::kInt64Sub:
-        return VisitWord64Compare(selector, value, cont);
       case IrOpcode::kWord32And:
         return VisitWordCompare(selector, value, kX64Test32, cont);
-      case IrOpcode::kWord64And:
-        return VisitWordCompare(selector, value, kX64Test, cont);
       default:
         break;
     }
@@ -2155,32 +2151,7 @@ void InstructionSelector::VisitWord32Equal(Node* const node) {
   FlagsContinuation cont = FlagsContinuation::ForSet(kEqual, node);
   Int32BinopMatcher m(user);
   if (m.right().Is(0)) {
-    Node* value = m.left().node();
-
-    // Try to combine with comparisons against 0 by simply inverting the branch.
-    while (CanCover(user, value) && value->opcode() == IrOpcode::kWord32Equal) {
-      Int32BinopMatcher m(value);
-      if (m.right().Is(0)) {
-        user = value;
-        value = m.left().node();
-        cont.Negate();
-      } else {
-        break;
-      }
-    }
-
-    // Try to combine the branch with a comparison.
-    if (CanCover(user, value)) {
-      switch (value->opcode()) {
-        case IrOpcode::kInt32Sub:
-          return VisitWordCompare(this, value, kX64Cmp32, &cont);
-        case IrOpcode::kWord32And:
-          return VisitWordCompare(this, value, kX64Test32, &cont);
-        default:
-          break;
-      }
-    }
-    return VisitCompareZero(this, value, kX64Cmp32, &cont);
+    return VisitWordCompareZero(this, m.node(), m.left().node(), &cont);
   }
   VisitWordCompare(this, node, kX64Cmp32, &cont);
 }