[arm64] Remove dead StoreRegistersState and RestoreRegisterState stubs.

Also remove UnsafeAcquire from UseScratchRegisterScope, which was only used for
these stubs.

Bug: 
Change-Id: Ia8648e53f1165ae489c0475dbb2d10c6978e4e84
Reviewed-on: https://chromium-review.googlesource.com/576181Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Cr-Commit-Position: refs/heads/master@{#46761}

src/arm64/code-stubs-arm64.cc

@@ -621,30 +621,6 @@ void StoreBufferOverflowStub::GenerateFixedRegStubsAheadOfTime(
 }
 
 
-void StoreRegistersStateStub::Generate(MacroAssembler* masm) {
-  MacroAssembler::NoUseRealAbortsScope no_use_real_aborts(masm);
-  UseScratchRegisterScope temps(masm);
-  Register saved_lr = temps.UnsafeAcquire(to_be_pushed_lr());
-  Register return_address = temps.AcquireX();
-  __ Mov(return_address, lr);
-  // Restore lr with the value it had before the call to this stub (the value
-  // which must be pushed).
-  __ Mov(lr, saved_lr);
-  __ PushSafepointRegisters();
-  __ Ret(return_address);
-}
-
-
-void RestoreRegistersStateStub::Generate(MacroAssembler* masm) {
-  MacroAssembler::NoUseRealAbortsScope no_use_real_aborts(masm);
-  UseScratchRegisterScope temps(masm);
-  Register return_address = temps.AcquireX();
-  // Preserve the return address (lr will be clobbered by the pop).
-  __ Mov(return_address, lr);
-  __ PopSafepointRegisters();
-  __ Ret(return_address);
-}
-
 void MathPowStub::Generate(MacroAssembler* masm) {
   // Stack on entry:
   // jssp[0]: Exponent (as a tagged value).
@@ -777,24 +753,10 @@ void CodeStub::GenerateStubsAheadOfTime(Isolate* isolate) {
   CommonArrayConstructorStub::GenerateStubsAheadOfTime(isolate);
   CreateAllocationSiteStub::GenerateAheadOfTime(isolate);
   CreateWeakCellStub::GenerateAheadOfTime(isolate);
-  StoreRegistersStateStub::GenerateAheadOfTime(isolate);
-  RestoreRegistersStateStub::GenerateAheadOfTime(isolate);
   StoreFastElementStub::GenerateAheadOfTime(isolate);
 }
 
 
-void StoreRegistersStateStub::GenerateAheadOfTime(Isolate* isolate) {
-  StoreRegistersStateStub stub(isolate);
-  stub.GetCode();
-}
-
-
-void RestoreRegistersStateStub::GenerateAheadOfTime(Isolate* isolate) {
-  RestoreRegistersStateStub stub(isolate);
-  stub.GetCode();
-}
-
-
 void CodeStub::GenerateFPStubs(Isolate* isolate) {
   // Floating-point code doesn't get special handling in ARM64, so there's
   // nothing to do here.

src/arm64/code-stubs-arm64.h

@@ -35,34 +35,6 @@ class StringHelper : public AllStatic {
 };
 
 
-class StoreRegistersStateStub: public PlatformCodeStub {
- public:
-  explicit StoreRegistersStateStub(Isolate* isolate)
-      : PlatformCodeStub(isolate) {}
-
-  static Register to_be_pushed_lr() { return ip0; }
-
-  static void GenerateAheadOfTime(Isolate* isolate);
-
- private:
-  DEFINE_NULL_CALL_INTERFACE_DESCRIPTOR();
-  DEFINE_PLATFORM_CODE_STUB(StoreRegistersState, PlatformCodeStub);
-};
-
-
-class RestoreRegistersStateStub: public PlatformCodeStub {
- public:
-  explicit RestoreRegistersStateStub(Isolate* isolate)
-      : PlatformCodeStub(isolate) {}
-
-  static void GenerateAheadOfTime(Isolate* isolate);
-
- private:
-  DEFINE_NULL_CALL_INTERFACE_DESCRIPTOR();
-  DEFINE_PLATFORM_CODE_STUB(RestoreRegistersState, PlatformCodeStub);
-};
-
-
 class RecordWriteStub: public PlatformCodeStub {
  public:
   // Stub to record the write of 'value' at 'address' in 'object'.

src/arm64/macro-assembler-arm64.cc

@@ -4233,13 +4233,6 @@ CPURegister UseScratchRegisterScope::AcquireNextAvailable(
 }
 
 
-CPURegister UseScratchRegisterScope::UnsafeAcquire(CPURegList* available,
-                                                   const CPURegister& reg) {
-  DCHECK(available->IncludesAliasOf(reg));
-  available->Remove(reg);
-  return reg;
-}
-
 MemOperand ContextMemOperand(Register context, int index) {
   return MemOperand(context, Context::SlotOffset(index));
 }

src/arm64/macro-assembler-arm64.h

@@ -2496,17 +2496,11 @@ class UseScratchRegisterScope {
     return VRegister::Create(AcquireNextAvailable(availablefp_).code(), format);
   }
 
-  Register UnsafeAcquire(const Register& reg) {
-    return Register(UnsafeAcquire(available_, reg));
-  }
-
   Register AcquireSameSizeAs(const Register& reg);
   VRegister AcquireSameSizeAs(const VRegister& reg);
 
  private:
   static CPURegister AcquireNextAvailable(CPURegList* available);
-  static CPURegister UnsafeAcquire(CPURegList* available,
-                                   const CPURegister& reg);
 
   // Available scratch registers.
   CPURegList* available_;     // kRegister

src/code-stubs.h

@@ -87,10 +87,7 @@ class Node;
 
 // List of code stubs only used on ARM 64 bits platforms.
 #if V8_TARGET_ARCH_ARM64
-#define CODE_STUB_LIST_ARM64(V) \
-  V(DirectCEntry)               \
-  V(RestoreRegistersState)      \
-  V(StoreRegistersState)
+#define CODE_STUB_LIST_ARM64(V) V(DirectCEntry)
 
 #else
 #define CODE_STUB_LIST_ARM64(V)