[turbofan] Fix invalid comparison operator narrowing.

src/compiler/instruction-selector-impl.h

 // 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.
 
 #ifndef V8_COMPILER_INSTRUCTION_SELECTOR_IMPL_H_
 #define V8_COMPILER_INSTRUCTION_SELECTOR_IMPL_H_
 
 #include "src/compiler/instruction.h"
 #include "src/compiler/instruction-selector.h"
 #include "src/compiler/linkage.h"
@@ skipping 368 matching lines @@
   }
 
   void Overwrite(FlagsCondition condition) { condition_ = condition; }
 
   void OverwriteAndNegateIfEqual(FlagsCondition condition) {
     bool negate = condition_ == kEqual;
     condition_ = condition;
     if (negate) Negate();
   }
 
+  void OverwriteUnsignedIfSigned() {
+    switch (condition_) {
+      case kSignedLessThan:
+        condition_ = kUnsignedLessThan;
+        break;
+      case kSignedLessThanOrEqual:
+        condition_ = kUnsignedLessThanOrEqual;
+        break;
+      case kSignedGreaterThan:
+        condition_ = kUnsignedGreaterThan;
+        break;
+      case kSignedGreaterThanOrEqual:
+        condition_ = kUnsignedGreaterThanOrEqual;
+        break;
+      default:
+        break;
+    }
+  }
+
   // Encodes this flags continuation into the given opcode.
   InstructionCode Encode(InstructionCode opcode) {
     opcode |= FlagsModeField::encode(mode_);
     if (mode_ != kFlags_none) {
       opcode |= FlagsConditionField::encode(condition_);
     }
     return opcode;
   }
 
  private:
@@ skipping 19 matching lines @@
                                  // or mode_ == kFlags_set.
   BasicBlock* true_block_;       // Only valid if mode_ == kFlags_branch.
   BasicBlock* false_block_;      // Only valid if mode_ == kFlags_branch.
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_SELECTOR_IMPL_H_