Optimize AOT's switchable calls for the monomorphic case.

runtime/vm/assembler_arm64.cc

Index: runtime/vm/assembler_arm64.cc
diff --git a/runtime/vm/assembler_arm64.cc b/runtime/vm/assembler_arm64.cc
index 54dcabbf927d2d98641db8c615c0b9fe617ce104..6535eb0575981038c786f1b2341dff964112799c 100644
--- a/runtime/vm/assembler_arm64.cc
+++ b/runtime/vm/assembler_arm64.cc
@@ -33,6 +33,7 @@ Assembler::Assembler(bool use_far_branches)
       use_far_branches_(use_far_branches),
       comments_(),
       constant_pool_allowed_(false) {
+  MonomorphicCheckedEntry();
 }
 
 
@@ -1243,6 +1244,53 @@ void Assembler::LeaveStubFrame() {
 }
 
 
+void Assembler::NoMonomorphicCheckedEntry() {
+  buffer_.Reset();
+  brk(0);
+  brk(0);
+  brk(0);
+  brk(0);
+  brk(0);
+  brk(0);
+  ASSERT(CodeSize() == Instructions::kCheckedEntryOffset);
+}
+
+
+// R0 receiver, R5 guarded cid as Smi
+void Assembler::MonomorphicCheckedEntry() {
+  bool saved_use_far_branches = use_far_branches();
+  set_use_far_branches(false);
+
+  Label immediate, have_cid, miss;
+  Bind(&miss);
+  ldr(CODE_REG, Address(THR, Thread::monomorphic_miss_stub_offset()));
+  ldr(IP0, FieldAddress(CODE_REG, Code::entry_point_offset()));
+  br(IP0);
+  brk(0);
+
+  Bind(&immediate);
+  movz(R1, Immediate(kSmiCid), 0);
+  b(&have_cid);
+
+  Comment("MonomorphicCheckedEntry");
+  ASSERT(CodeSize() == Instructions::kCheckedEntryOffset);
+  tsti(R0, Immediate(kSmiTagMask));
+  SmiUntag(R5);
+  b(&immediate, EQ);
+
+  LoadClassId(R1, R0);
+
+  Bind(&have_cid);
+  cmp(R1, Operand(R5));
+  b(&miss, NE);
+
+  // Fall through to unchecked entry.
+  ASSERT(CodeSize() == Instructions::kUncheckedEntryOffset);
+
+  set_use_far_branches(saved_use_far_branches);
+}
+
+
 #ifndef PRODUCT
 void Assembler::MaybeTraceAllocation(intptr_t cid,
                                      Register temp_reg,