Optimizing: Improve const-string code generation.

For strings in the boot image, use either direct pointers
or pc-relative addresses. For other strings, use PC-relative
access to the dex cache arrays for AOT and direct address of
the string's dex cache slot for JIT.

For aosp_flounder-userdebug:
  - 32-bit boot.oat: -692KiB (-0.9%)
  - 64-bit boot.oat: -948KiB (-1.1%)
  - 32-bit dalvik cache total: -900KiB (-0.9%)
  - 64-bit dalvik cache total: -3672KiB (-1.5%)
    (contains more files than the 32-bit dalvik cache)
For aosp_flounder-userdebug forced to compile PIC:
  - 32-bit boot.oat: -380KiB (-0.5%)
  - 64-bit boot.oat: -928KiB (-1.0%)
  - 32-bit dalvik cache total: -468KiB (-0.4%)
  - 64-bit dalvik cache total: -1928KiB (-0.8%)
    (contains more files than the 32-bit dalvik cache)

Bug: 26884697
Change-Id: Iec7266ce67e6fedc107be78fab2e742a8dab2696
diff --git a/compiler/optimizing/code_generator_x86_64.h b/compiler/optimizing/code_generator_x86_64.h
index c3fce6e..fdcf3c3 100644
--- a/compiler/optimizing/code_generator_x86_64.h
+++ b/compiler/optimizing/code_generator_x86_64.h
@@ -252,13 +252,13 @@
                                          Location maybe_temp);
   // Generate a GC root reference load:
   //
-  //   root <- *(obj + offset)
+  //   root <- *address
   //
   // while honoring read barriers (if any).
   void GenerateGcRootFieldLoad(HInstruction* instruction,
                                Location root,
-                               CpuRegister obj,
-                               uint32_t offset);
+                               const Address& address,
+                               Label* fixup_label = nullptr);
 
   void PushOntoFPStack(Location source, uint32_t temp_offset,
                        uint32_t stack_adjustment, bool is_float);
@@ -384,6 +384,11 @@
     return false;
   }
 
+  // Check if the desired_string_load_kind is supported. If it is, return it,
+  // otherwise return a fall-back kind that should be used instead.
+  HLoadString::LoadKind GetSupportedLoadStringKind(
+      HLoadString::LoadKind desired_string_load_kind) OVERRIDE;
+
   // Check if the desired_dispatch_info is supported. If it is, return it,
   // otherwise return a fall-back info that should be used instead.
   HInvokeStaticOrDirect::DispatchInfo GetSupportedInvokeStaticOrDirectDispatch(
@@ -393,6 +398,10 @@
   void GenerateStaticOrDirectCall(HInvokeStaticOrDirect* invoke, Location temp) OVERRIDE;
   void GenerateVirtualCall(HInvokeVirtual* invoke, Location temp) OVERRIDE;
 
+  void RecordSimplePatch();
+  void RecordStringPatch(HLoadString* load_string);
+  Label* NewPcRelativeDexCacheArrayPatch(const DexFile& dex_file, uint32_t element_offset);
+
   void MoveFromReturnRegister(Location trg, Primitive::Type type) OVERRIDE;
 
   void EmitLinkerPatches(ArenaVector<LinkerPatch>* linker_patches) OVERRIDE;
@@ -515,6 +524,10 @@
   void GenerateImplicitNullCheck(HNullCheck* instruction);
   void GenerateExplicitNullCheck(HNullCheck* instruction);
 
+  // When we don't know the proper offset for the value, we use kDummy32BitOffset.
+  // We will fix this up in the linker later to have the right value.
+  static constexpr int32_t kDummy32BitOffset = 256;
+
  private:
   // Factored implementation of GenerateFieldLoadWithBakerReadBarrier
   // and GenerateArrayLoadWithBakerReadBarrier.
@@ -552,10 +565,10 @@
   ArenaDeque<MethodPatchInfo<Label>> relative_call_patches_;
   // PC-relative DexCache access info.
   ArenaDeque<PcRelativeDexCacheAccessInfo> pc_relative_dex_cache_patches_;
-
-  // When we don't know the proper offset for the value, we use kDummy32BitOffset.
-  // We will fix this up in the linker later to have the right value.
-  static constexpr int32_t kDummy32BitOffset = 256;
+  // Patch locations for patchoat where the linker doesn't do any other work.
+  ArenaDeque<Label> simple_patches_;
+  // String patch locations.
+  ArenaDeque<StringPatchInfo<Label>> string_patches_;
 
   // Fixups for jump tables need to be handled specially.
   ArenaVector<JumpTableRIPFixup*> fixups_to_jump_tables_;