Remove dead code from InvokeDartCode stub.

runtime/vm/stub_code_arm64.cc

Index: runtime/vm/stub_code_arm64.cc
===================================================================
--- runtime/vm/stub_code_arm64.cc	(revision 41310)
+++ runtime/vm/stub_code_arm64.cc	(working copy)
@@ -812,9 +812,6 @@
 //   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.
@@ -841,6 +838,9 @@
 #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);
@@ -866,9 +866,6 @@
   // 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);
@@ -930,10 +927,6 @@
   // 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);