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

src/compiler/mips64/instruction-selector-mips64.cc

Index: src/compiler/mips64/instruction-selector-mips64.cc
diff --git a/src/compiler/mips64/instruction-selector-mips64.cc b/src/compiler/mips64/instruction-selector-mips64.cc
index 6f72c6451d1fb920c0aae444f7cf1dbeb3ff6182..93d51d3df3fab3f3bc81e2188927184d2300c8ca 100644
--- a/src/compiler/mips64/instruction-selector-mips64.cc
+++ b/src/compiler/mips64/instruction-selector-mips64.cc
@@ -2037,21 +2037,30 @@ void EmitWordCompareZero(InstructionSelector* selector, Node* value,
 // Shared routine for word comparisons against zero.
 void VisitWordCompareZero(InstructionSelector* selector, Node* user,
                           Node* value, FlagsContinuation* cont) {
+  // Try to combine with comparisons against 0 by simply inverting the branch.
   while (selector->CanCover(user, value)) {
+    if (value->opcode() == IrOpcode::kWord32Equal) {
+      Int32BinopMatcher m(value);
+      if (!m.right().Is(0)) break;
+      user = value;
+      value = m.left().node();
+    } else if (value->opcode() == IrOpcode::kWord64Equal) {
+      Int64BinopMatcher m(value);
+      if (!m.right().Is(0)) break;
+      user = value;
+      value = m.left().node();
+    } else {
+      break;
+    }
+
+    cont->Negate();
+  }
+
+  if (selector->CanCover(user, value)) {
     switch (value->opcode()) {
-      case IrOpcode::kWord32Equal: {
-        // 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 VisitWord32Compare(selector, value, cont);
-      }
       case IrOpcode::kInt32LessThan:
         cont->OverwriteAndNegateIfEqual(kSignedLessThan);
         return VisitWord32Compare(selector, value, cont);
@@ -2064,19 +2073,9 @@ void VisitWordCompareZero(InstructionSelector* selector, Node* user,
       case IrOpcode::kUint32LessThanOrEqual:
         cont->OverwriteAndNegateIfEqual(kUnsignedLessThanOrEqual);
         return VisitWord32Compare(selector, value, cont);
-      case IrOpcode::kWord64Equal: {
-        // Combine with comparisons against 0 by simply inverting the
-        // continuation.
-        Int64BinopMatcher m(value);
-        if (m.right().Is(0)) {
-          user = value;
-          value = m.left().node();
-          cont->Negate();
-          continue;
-        }
+      case IrOpcode::kWord64Equal:
         cont->OverwriteAndNegateIfEqual(kEqual);
         return VisitWord64Compare(selector, value, cont);
-      }
       case IrOpcode::kInt64LessThan:
         cont->OverwriteAndNegateIfEqual(kSignedLessThan);
         return VisitWord64Compare(selector, value, cont);
@@ -2147,7 +2146,6 @@ void VisitWordCompareZero(InstructionSelector* selector, Node* user,
       default:
         break;
     }
-    break;
   }
 
   // Continuation could not be combined with a compare, emit compare against 0.