[turbofan] Refactor the compare-zero folding in instruction selector.

src/compiler/ia32/instruction-selector-ia32.cc

Index: src/compiler/ia32/instruction-selector-ia32.cc
diff --git a/src/compiler/ia32/instruction-selector-ia32.cc b/src/compiler/ia32/instruction-selector-ia32.cc
index 5637f3749f4d2afdd94aefdaf6d827292ceec954..c827c68a5ff3c69703c080b74e4c10f19988fa50 100644
--- a/src/compiler/ia32/instruction-selector-ia32.cc
+++ b/src/compiler/ia32/instruction-selector-ia32.cc
@@ -1393,22 +1393,22 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
 // Shared routine for word comparison with zero.
 void VisitWordCompareZero(InstructionSelector* selector, Node* user,
                           Node* value, FlagsContinuation* cont) {
-  // Try to combine the branch with a comparison.
-  while (selector->CanCover(user, value)) {
+  // Try to combine with comparisons against 0 by simply inverting the branch.
+  while (value->opcode() == IrOpcode::kWord32Equal &&
+         selector->CanCover(user, value)) {
+    Int32BinopMatcher m(value);
+    if (!m.right().Is(0)) break;
+
+    user = value;
+    value = m.left().node();
+    cont->Negate();
+  }
+
+  if (selector->CanCover(user, value)) {
     switch (value->opcode()) {
-      case IrOpcode::kWord32Equal: {
-        // Try to combine with comparisons against 0 by simply inverting the
-        // continuation.
-        Int32BinopMatcher m(value);
-        if (m.right().Is(0)) {
-          user = value;
-          value = m.left().node();
-          cont->Negate();
-          continue;
-        }
+      case IrOpcode::kWord32Equal:
         cont->OverwriteAndNegateIfEqual(kEqual);
         return VisitWordCompare(selector, value, cont);
-      }
       case IrOpcode::kInt32LessThan:
         cont->OverwriteAndNegateIfEqual(kSignedLessThan);
         return VisitWordCompare(selector, value, cont);
@@ -1474,7 +1474,6 @@ void VisitWordCompareZero(InstructionSelector* selector, Node* user,
       default:
         break;
     }
-    break;
   }
 
   // Continuation could not be combined with a compare, emit compare against 0.