[Turbofan] Reduce register allocation work when we can.

src/machine-type.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_MACHINE_TYPE_H_
 #define V8_MACHINE_TYPE_H_
 
 #include <iosfwd>
 
 #include "src/base/bits.h"
@@ skipping 11 matching lines @@
   kWord16,
   kWord32,
   kWord64,
   kTaggedSigned,
   kTaggedPointer,
   kTagged,
   // FP representations must be last, and in order of increasing size.
   kFloat32,
   kFloat64,
   kSimd128,
-  kFirstFPRepresentation = kFloat32
+  kFirstFPRepresentation = kFloat32,
+  kLastRepresentation = kSimd128
 };
 
+static_assert(static_cast<int>(MachineRepresentation::kLastRepresentation) <
+                  kIntSize * kBitsPerByte,
+              "Bit masks of MachineRepresentation should fit in an int");
+
 const char* MachineReprToString(MachineRepresentation);
 
 enum class MachineSemantic : uint8_t {
   kNone,
   kBool,
   kInt32,
   kUint32,
   kInt64,
   kUint64,
   kNumber,
@@ skipping 219 matching lines @@
   UNREACHABLE();
   return -1;
 }
 
 typedef Signature<MachineType> MachineSignature;
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_MACHINE_TYPE_H_