Enables first codegen test on arm64.

runtime/vm/assembler_arm64.h

Index: runtime/vm/assembler_arm64.h
===================================================================
--- runtime/vm/assembler_arm64.h	(revision 35315)
+++ runtime/vm/assembler_arm64.h	(working copy)
@@ -410,6 +410,8 @@
   static bool IsSafeSmi(const Object& object) { return object.IsSmi(); }
 
   // Addition and subtraction.
+  // For add and sub, to use SP for rn, o must be of type Operand::Extend.
+  // For an unmodified rm in this case, use Operand(rm, UXTX, 0);
   void add(Register rd, Register rn, Operand o) {
     AddSubHelper(kDoubleWord, false, false, rd, rn, o);
   }
@@ -542,6 +544,8 @@
 
   // Comparison.
   // rn cmp o.
+  // For add and sub, to use SP for rn, o must be of type Operand::Extend.
+  // For an unmodified rm in this case, use Operand(rm, UXTX, 0);
   void cmp(Register rn, Operand o) {
     subs(ZR, rn, o);
   }
@@ -550,6 +554,16 @@
     adds(ZR, rn, o);
   }
 
+  void CompareRegisters(Register rn, Register rm) {
+    if (rn == SP) {
+      // UXTX 0 on a 64-bit register (rm) is a nop, but forces R31 to be
+      // interpreted as SP.
+      cmp(SP, Operand(rm, UXTX, 0));
+    } else {
+      cmp(rn, Operand(rm));
+    }
+  }
+
   // Conditional branch.
   void b(Label* label, Condition cond = AL) {
     EmitBranch(BCOND, cond, label);
@@ -633,16 +647,22 @@
   }
 
   // Branching to ExternalLabels.
-  void Branch(const ExternalLabel* label) {
-    LoadExternalLabel(TMP, label, kPatchable, PP);
+  void BranchPatchable(const ExternalLabel* label, Register pp) {
+    LoadExternalLabel(TMP, label, kPatchable, pp);
     br(TMP);
   }
 
-  void BranchPatchable(const ExternalLabel* label) {
-    LoadPatchableImmediate(TMP, label->address());
+  void Branch(const ExternalLabel* label, Register pp) {
+    LoadExternalLabel(TMP, label, kNotPatchable, pp);
     br(TMP);
   }
 
+  // Fixed length branch to label.
+  void BranchFixed(const ExternalLabel* label) {
+    LoadImmediateFixed(TMP, label->address());
+    br(TMP);
+  }
+
   void BranchLink(const ExternalLabel* label, Register pp) {
     if (Isolate::Current() == Dart::vm_isolate()) {
       LoadImmediate(TMP, label->address(), kNoRegister);
@@ -704,7 +724,7 @@
                          Patchability patchable, Register pp);
   void LoadObject(Register dst, const Object& obj, Register pp);
   void LoadDecodableImmediate(Register reg, int64_t imm, Register pp);
-  void LoadPatchableImmediate(Register reg, int64_t imm);
+  void LoadImmediateFixed(Register reg, int64_t imm);
   void LoadImmediate(Register reg, int64_t imm, Register pp);
 
   void PushObject(const Object& object, Register pp) {
@@ -716,6 +736,8 @@
   void LeaveFrame();
 
   void EnterDartFrame(intptr_t frame_size);
+  void EnterDartFrameWithInfo(intptr_t frame_size, Register new_pp);
+  void EnterOsrFrame(intptr_t extra_size, Register new_pp);
   void LeaveDartFrame();
 
   void EnterCallRuntimeFrame(intptr_t frame_size);