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

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

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/base/adapters.h"
 #include "src/base/bits.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
@@ skipping 1398 matching lines @@
 
 
 void VisitWordCompare(InstructionSelector* selector, Node* node,
                       FlagsContinuation* cont) {
   VisitWordCompare(selector, node, kMipsCmp, cont, false);
 }
 
 // Shared routine for word comparisons against zero.
 void VisitWordCompareZero(InstructionSelector* selector, Node* user,
                           Node* value, FlagsContinuation* cont) {
-  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: {
-        // 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);
       case IrOpcode::kInt32LessThanOrEqual:
         cont->OverwriteAndNegateIfEqual(kSignedLessThanOrEqual);
         return VisitWordCompare(selector, value, cont);
       case IrOpcode::kUint32LessThan:
         cont->OverwriteAndNegateIfEqual(kUnsignedLessThan);
         return VisitWordCompare(selector, value, cont);
       case IrOpcode::kUint32LessThanOrEqual:
@@ skipping 43 matching lines @@
                 break;
             }
           }
         }
         break;
       case IrOpcode::kWord32And:
         return VisitWordCompare(selector, value, kMipsTst, cont, true);
       default:
         break;
     }
-    break;
   }
 
   // Continuation could not be combined with a compare, emit compare against 0.
   MipsOperandGenerator g(selector);
   InstructionCode const opcode = cont->Encode(kMipsCmp);
   InstructionOperand const value_operand = g.UseRegister(value);
   if (cont->IsBranch()) {
     selector->Emit(opcode, g.NoOutput(), value_operand, g.TempImmediate(0),
                    g.Label(cont->true_block()), g.Label(cont->false_block()));
   } else if (cont->IsDeoptimize()) {
@@ skipping 299 matching lines @@
     DCHECK(IsMipsArchVariant(kLoongson) || IsMipsArchVariant(kMips32r1) ||
            IsMipsArchVariant(kMips32r2));
     return MachineOperatorBuilder::AlignmentRequirements::
         NoUnalignedAccessSupport();
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8