Compressed native PC for stack maps

Compress native PC based on instruction alignment. This reduces the
size of stack maps, boot.oat is 0.4% smaller for arm64.

Test: test-art-host, test-art-target, N6P booting

Change-Id: I2b70eecabda88b06fa80a85688fd992070d54278
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index 70c2738..99427f0 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -839,8 +839,8 @@
     // last emitted is different than the native pc of the stack map just emitted.
     size_t number_of_stack_maps = stack_map_stream_.GetNumberOfStackMaps();
     if (number_of_stack_maps > 1) {
-      DCHECK_NE(stack_map_stream_.GetStackMap(number_of_stack_maps - 1).native_pc_offset,
-                stack_map_stream_.GetStackMap(number_of_stack_maps - 2).native_pc_offset);
+      DCHECK_NE(stack_map_stream_.GetStackMap(number_of_stack_maps - 1).native_pc_code_offset,
+                stack_map_stream_.GetStackMap(number_of_stack_maps - 2).native_pc_code_offset);
     }
   }
 }
@@ -848,7 +848,8 @@
 bool CodeGenerator::HasStackMapAtCurrentPc() {
   uint32_t pc = GetAssembler()->CodeSize();
   size_t count = stack_map_stream_.GetNumberOfStackMaps();
-  return count > 0 && stack_map_stream_.GetStackMap(count - 1).native_pc_offset == pc;
+  CodeOffset native_pc_offset = stack_map_stream_.GetStackMap(count - 1).native_pc_code_offset;
+  return (count > 0) && (native_pc_offset.Uint32Value(GetInstructionSet()) == pc);
 }
 
 void CodeGenerator::MaybeRecordNativeDebugInfo(HInstruction* instruction,