Reland - Arm64: Ensure that csp is always aligned to 16 byte values even if jssp is not.

src/arm64/cpu-arm64.h

 // Copyright 2013 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_ARM64_CPU_ARM64_H_
 #define V8_ARM64_CPU_ARM64_H_
 
 #include <stdio.h>
 #include "serialize.h"
 #include "cpu.h"
 
 namespace v8 {
 namespace internal {
 
 
 // CpuFeatures keeps track of which features are supported by the target CPU.
 // Supported features must be enabled by a CpuFeatureScope before use.
 class CpuFeatures : public AllStatic {
  public:
   // Detect features of the target CPU. Set safe defaults if the serializer
   // is enabled (snapshots must be portable).
   static void Probe(bool serializer_enabled);
 
   // Check whether a feature is supported by the target CPU.
   static bool IsSupported(CpuFeature f) {
     ASSERT(initialized_);
-    // There are no optional features for ARM64.
-    return false;
+    return Check(f, supported_);
   };
 
-  // There are no optional features for ARM64.
   static bool IsSafeForSnapshot(Isolate* isolate, CpuFeature f) {
     return IsSupported(f);
   }
 
   // I and D cache line size in bytes.
   static unsigned dcache_line_size();
   static unsigned icache_line_size();
 
   static unsigned supported_;
 
   static bool VerifyCrossCompiling() {
-    // There are no optional features for ARM64.
-    ASSERT(cross_compile_ == 0);
-    return true;
+    return cross_compile_ == 0;
   }
 
   static bool VerifyCrossCompiling(CpuFeature f) {
-    // There are no optional features for ARM64.
-    USE(f);
-    ASSERT(cross_compile_ == 0);
-    return true;
+    unsigned mask = flag2set(f);
+    return cross_compile_ == 0 ||
+           (cross_compile_ & mask) == mask;
   }
 
   static bool SupportsCrankshaft() { return true; }
 
  private:
 #ifdef DEBUG
   static bool initialized_;
 #endif
 
-  // This isn't used (and is always 0), but it is required by V8.
+  static unsigned found_by_runtime_probing_only_;
   static unsigned cross_compile_;
 
+  static bool Check(CpuFeature f, unsigned set) {
+    return (set & flag2set(f)) != 0;
+  }
+
+  static unsigned flag2set(CpuFeature f) {
+    return 1u << f;
+  }
+
   friend class PlatformFeatureScope;
   DISALLOW_COPY_AND_ASSIGN(CpuFeatures);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM64_CPU_ARM64_H_