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

src/compiler/arm64/instruction-selector-arm64.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/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 2335 matching lines @@
                  g.UseImmediate(m.left().node()), cont);
   } else {
     VisitCompare(selector, kArm64Float64Cmp, g.UseRegister(m.left().node()),
                  g.UseRegister(m.right().node()), cont);
   }
 }
 
 void VisitWordCompareZero(InstructionSelector* selector, Node* user,
                           Node* value, FlagsContinuation* cont) {
   Arm64OperandGenerator g(selector);
-  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 VisitWord32Compare(selector, value, cont);
-      }
       case IrOpcode::kInt32LessThan:
         cont->OverwriteAndNegateIfEqual(kSignedLessThan);
         return VisitWord32Compare(selector, value, cont);
       case IrOpcode::kInt32LessThanOrEqual:
         cont->OverwriteAndNegateIfEqual(kSignedLessThanOrEqual);
         return VisitWord32Compare(selector, value, cont);
       case IrOpcode::kUint32LessThan:
         cont->OverwriteAndNegateIfEqual(kUnsignedLessThan);
         return VisitWord32Compare(selector, value, cont);
       case IrOpcode::kUint32LessThanOrEqual:
@@ skipping 117 matching lines @@
       case IrOpcode::kWord64And:
         if (TryEmitTestAndBranch<Uint64BinopMatcher, kArm64TestAndBranch>(
                 selector, value, cont)) {
           return;
         }
         return VisitWordCompare(selector, value, kArm64Tst, cont, true,
                                 kLogical64Imm);
       default:
         break;
     }
-    break;
   }
 
   // Branch could not be combined with a compare, compare against 0 and branch.
   if (cont->IsBranch()) {
     selector->Emit(cont->Encode(kArm64CompareAndBranch32), g.NoOutput(),
                    g.UseRegister(value), g.Label(cont->true_block()),
                    g.Label(cont->false_block()));
   } else {
     DCHECK(cont->IsDeoptimize());
     selector->EmitDeoptimize(cont->Encode(kArm64Tst32), g.NoOutput(),
@@ skipping 386 matching lines @@
 // static
 MachineOperatorBuilder::AlignmentRequirements
 InstructionSelector::AlignmentRequirements() {
   return MachineOperatorBuilder::AlignmentRequirements::
       FullUnalignedAccessSupport();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8