Move caller-saves saving/restoring to ReadBarrierMarkRegX.

Instead of saving/restoring live caller-save registers
before/after the call to read barrier mark entry points
ReadBarrierMarkRegX, have these entry points save/restore
all the caller-save registers themselves (except register
rX, which contains the return value).

Also refactor the assembly code of these entry points
using macros.

* Boot image code size variation on Nexus 5X
  (aosp_bullhead-userdebug build):
  - total ARM64 framework Oat files size change:
    119196792 bytes -> 115575920 bytes (-3.04%)
  - total ARM framework Oat files size change:
    100435212 bytes -> 97621188 bytes (-2.80%)

* Benchmarks (ARM64) score variations on Nexus 5X
  (aosp_bullhead-userdebug build):
  - RitzPerf (lower is better)
    - average score difference: -2.71%
  - CaffeineMark (higher is better)
    - no real difference for most tests
      (absolute variation lower than 1%)
    - better score on the "Method" benchmark:
      score variation 41253 -> 44891 (+8.82%)

Test: ART host and target (ARM, ARM64) tests.
Bug: 29506760
Bug: 12687968
Change-Id: I881bf73139a3f1c2bee9ffc6fc8c00f9a392afa6

1 files changed, 3 insertions, 7 deletions

diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index 1aa7b5404c..474e9d540a 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -437,11 +437,9 @@ class ReadBarrierMarkSlowPathARM : public SlowPathCode {
         << instruction_->DebugName();
 
     __ Bind(GetEntryLabel());
-    // Save live registers before the runtime call, and in particular
-    // R0 (if it is live), as it is clobbered by functions
-    // art_quick_read_barrier_mark_regX.
-    SaveLiveRegisters(codegen, locations);
-
+    // No need to save live registers; it's taken care of by the
+    // entrypoint. Also, there is no need to update the stack mask,
+    // as this runtime call will not trigger a garbage collection.
     InvokeRuntimeCallingConvention calling_convention;
     CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen);
     DCHECK_NE(reg, SP);
@@ -469,8 +467,6 @@ class ReadBarrierMarkSlowPathARM : public SlowPathCode {
                                instruction_,
                                instruction_->GetDexPc(),
                                this);
-
-    RestoreLiveRegisters(codegen, locations);
     __ b(GetExitLabel());
   }