Remove dead code from InvokeDartCode stub.

runtime/vm/stub_code_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 794 matching lines @@
 
 // Called when invoking Dart code from C++ (VM code).
 // Input parameters:
 //   LR : points to return address.
 //   R0 : entrypoint of the Dart function to call.
 //   R1 : arguments descriptor array.
 //   R2 : arguments array.
 //   R3 : new context containing the current isolate pointer.
 void StubCode::GenerateInvokeDartCodeStub(Assembler* assembler) {
   __ Comment("InvokeDartCodeStub");
-  // The new context, saved vm tag, the top exit frame, and the old context.
-  const intptr_t kNewContextOffsetFromFp =
-      -(1 + kAbiPreservedCpuRegCount + kAbiPreservedFpuRegCount) * kWordSize;
 
   // Copy the C stack pointer (R31) into the stack pointer we'll actually use
   // to access the stack, and put the C stack pointer at the stack limit.
   __ SetupDartSP(Isolate::GetSpecifiedStackSize());
   __ EnterFrame(0);
 
   // Save the callee-saved registers.
   for (int i = kAbiFirstPreservedCpuReg; i <= kAbiLastPreservedCpuReg; i++) {
     const Register r = static_cast<Register>(i);
     // We use str instead of the Push macro because we will be pushing the PP
     // register when it is not holding a pool-pointer since we are coming from
     // C++ code.
     __ str(r, Address(SP, -1 * kWordSize, Address::PreIndex));
   }
 
   // Save the bottom 64-bits of callee-saved V registers.
   for (int i = kAbiFirstPreservedFpuReg; i <= kAbiLastPreservedFpuReg; i++) {
     const VRegister r = static_cast<VRegister>(i);
     __ PushDouble(r);
   }
 
   // Push new context.
   __ Push(R3);
 #if defined(DEBUG)
   {
     Label ok;
+    // The new context, saved vm tag, the top exit frame, and the old context.
+    const intptr_t kNewContextOffsetFromFp =
+        -(1 + kAbiPreservedCpuRegCount + kAbiPreservedFpuRegCount) * kWordSize;
     __ AddImmediate(R4, FP, kNewContextOffsetFromFp, kNoPP);
     __ CompareRegisters(R4, SP);
     __ b(&ok, EQ);
     __ Stop("kNewContextOffsetFromFp mismatch");
     __ Bind(&ok);
   }
 #endif
 
   // We now load the pool pointer(PP) as we are about to invoke dart code and we
   // could potentially invoke some intrinsic functions which need the PP to be
   // set up.
   __ LoadPoolPointer(PP);
 
   // The new Context structure contains a pointer to the current Isolate
   // structure. Cache the Context pointer in the CTX register so that it is
   // available in generated code and calls to Isolate::Current() need not be
   // done. The assumption is that this register will never be clobbered by
   // compiled or runtime stub code.
 
   // Cache the new Context pointer into CTX while executing Dart code.
   __ LoadFromOffset(CTX, R3, VMHandles::kOffsetOfRawPtrInHandle, PP);
 
   // Load Isolate pointer into temporary register R5.
   __ LoadIsolate(R5, PP);
 
-  // Cache the new Context pointer into CTX while executing Dart code.
-  __ LoadFromOffset(CTX, R3, VMHandles::kOffsetOfRawPtrInHandle, PP);
-
   // Save the current VMTag on the stack.
   ASSERT(kSavedVMTagSlotFromEntryFp == -20);
   __ LoadFromOffset(R4, R5, Isolate::vm_tag_offset(), PP);
   __ Push(R4);
 
   // Mark that the isolate is executing Dart code.
   __ LoadImmediate(R6, VMTag::kDartTagId, PP);
   __ StoreToOffset(R6, R5, Isolate::vm_tag_offset(), PP);
 
   // Save the top exit frame info. Use R6 as a temporary register.
@@ skipping 41 matching lines @@
   __ b(&push_arguments, LT);
   __ Bind(&done_push_arguments);
 
   // Call the Dart code entrypoint.
   __ blr(R0);  // R4 is the arguments descriptor array.
   __ Comment("InvokeDartCodeStub return");
 
   // Restore constant pool pointer after return.
   __ LoadPoolPointer(PP);
 
-  // Read the saved new Context pointer.
-  __ LoadFromOffset(CTX, FP, kNewContextOffsetFromFp, PP);
-  __ LoadFromOffset(CTX, CTX, VMHandles::kOffsetOfRawPtrInHandle, PP);
-
   // Get rid of arguments pushed on the stack.
   __ AddImmediate(SP, FP, kSavedContextSlotFromEntryFp * kWordSize, PP);
 
   // Load Isolate pointer into CTX. Drop Context.
   __ LoadIsolate(CTX, PP);
 
   // Restore the current VMTag from the stack.
   __ ldr(R4, Address(SP, 2 * kWordSize));
   __ StoreToOffset(R4, CTX, Isolate::vm_tag_offset(), PP);
 
@@ skipping 1164 matching lines @@
   const Register right = R0;
   __ LoadFromOffset(left, SP, 1 * kWordSize, kNoPP);
   __ LoadFromOffset(right, SP, 0 * kWordSize, kNoPP);
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64