Revert "Revert "Optimize IMT""

This reverts commit 88f288e3564d79d87c0cd8bb831ec5a791ba4861.

Change-Id: I49605d53692cbec1e2622e23ff2893fc51ed4115
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index fc2c2c3..c8d33d5 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -3506,8 +3506,6 @@
   // TODO: b/18116999, our IMTs can miss an IncompatibleClassChangeError.
   LocationSummary* locations = invoke->GetLocations();
   Register temp = XRegisterFrom(locations->GetTemp(0));
-  uint32_t method_offset = mirror::Class::EmbeddedImTableEntryOffset(
-      invoke->GetImtIndex() % mirror::Class::kImtSize, kArm64PointerSize).Uint32Value();
   Location receiver = locations->InAt(0);
   Offset class_offset = mirror::Object::ClassOffset();
   Offset entry_point = ArtMethod::EntryPointFromQuickCompiledCodeOffset(kArm64WordSize);
@@ -3537,6 +3535,10 @@
   // intact/accessible until the end of the marking phase (the
   // concurrent copying collector may not in the future).
   GetAssembler()->MaybeUnpoisonHeapReference(temp.W());
+  __ Ldr(temp,
+      MemOperand(temp, mirror::Class::ImtPtrOffset(kArm64PointerSize).Uint32Value()));
+  uint32_t method_offset = static_cast<uint32_t>(ImTable::OffsetOfElement(
+      invoke->GetImtIndex() % ImTable::kSize, kArm64PointerSize));
   // temp = temp->GetImtEntryAt(method_offset);
   __ Ldr(temp, MemOperand(temp, method_offset));
   // lr = temp->GetEntryPoint();
@@ -5353,8 +5355,10 @@
     method_offset = mirror::Class::EmbeddedVTableEntryOffset(
         instruction->GetIndex(), kArm64PointerSize).SizeValue();
   } else {
-    method_offset = mirror::Class::EmbeddedImTableEntryOffset(
-        instruction->GetIndex() % mirror::Class::kImtSize, kArm64PointerSize).Uint32Value();
+    __ Ldr(XRegisterFrom(locations->Out()), MemOperand(XRegisterFrom(locations->InAt(0)),
+        mirror::Class::ImtPtrOffset(kArm64PointerSize).Uint32Value()));
+    method_offset = static_cast<uint32_t>(ImTable::OffsetOfElement(
+        instruction->GetIndex() % ImTable::kSize, kArm64PointerSize));
   }
   __ Ldr(XRegisterFrom(locations->Out()),
          MemOperand(XRegisterFrom(locations->InAt(0)), method_offset));