Do not save/restore regs in ClinitCheck slow path.

The entrypoint is kSaveEverything, so the only register that
needs to be saved is the argument/return value register.

The size of the aosp_taimen-userdebug prebuilts:
  - before:
    arm/boot*.oat: 16811692
    arm64/boot*.oat: 19801032
    oat/arm64/services.odex: 20232208
  - after:
    arm/boot*.oat: 16798804 (-12.6KiB, -0.08%)
    arm64/boot*.oat: 19804392 (+3.3KiB, +0.02%)
    oat/arm64/services.odex: 20227784 (-4.3KiB, -0.02%)
Note that though there is less code, the metadata for the
arm64/boot*.oat outweighs the code size reduction because of
the register map encoding as value+shift introduced in
    https://android-review.googlesource.com/695682
which it's ill-suited for kSaveEverything entrypoints. We
should reconsider that encoding.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: Pixel 2 XL boots.
Test: testrunner.py --target --optimizing
Change-Id: I5cd1deb90332a3b88a0a59d87925c557d9bff1ab

1 files changed, 12 insertions, 8 deletions

diff --git a/compiler/optimizing/code_generator_mips.cc b/compiler/optimizing/code_generator_mips.cc
index 60bbf4c9f0..8b7479a861 100644
--- a/compiler/optimizing/code_generator_mips.cc
+++ b/compiler/optimizing/code_generator_mips.cc
@@ -160,6 +160,14 @@ Location InvokeRuntimeCallingConvention::GetReturnLocation(DataType::Type type)
   return MipsReturnLocation(type);
 }
 
+static RegisterSet OneRegInReferenceOutSaveEverythingCallerSaves() {
+  InvokeRuntimeCallingConvention calling_convention;
+  RegisterSet caller_saves = RegisterSet::Empty();
+  caller_saves.Add(Location::RegisterLocation(calling_convention.GetRegisterAt(0)));
+  // The reference is returned in the same register. This differs from the standard return location.
+  return caller_saves;
+}
+
 // NOLINT on __ macro to suppress wrong warning/fix (misc-macro-parentheses) from clang-tidy.
 #define __ down_cast<CodeGeneratorMIPS*>(codegen)->GetAssembler()->  // NOLINT
 #define QUICK_ENTRY_POINT(x) QUICK_ENTRYPOINT_OFFSET(kMipsPointerSize, x).Int32Value()
@@ -3594,6 +3602,8 @@ void LocationsBuilderMIPS::VisitClinitCheck(HClinitCheck* check) {
   if (check->HasUses()) {
     locations->SetOut(Location::SameAsFirstInput());
   }
+  // Rely on the type initialization to save everything we need.
+  locations->SetCustomSlowPathCallerSaves(OneRegInReferenceOutSaveEverythingCallerSaves());
 }
 
 void InstructionCodeGeneratorMIPS::VisitClinitCheck(HClinitCheck* check) {
@@ -8134,10 +8144,7 @@ void LocationsBuilderMIPS::VisitLoadClass(HLoadClass* cls) {
   if (load_kind == HLoadClass::LoadKind::kBssEntry) {
     if (!kUseReadBarrier || kUseBakerReadBarrier) {
       // Rely on the type resolution or initialization and marking to save everything we need.
-      RegisterSet caller_saves = RegisterSet::Empty();
-      InvokeRuntimeCallingConvention calling_convention;
-      caller_saves.Add(Location::RegisterLocation(calling_convention.GetRegisterAt(0)));
-      locations->SetCustomSlowPathCallerSaves(caller_saves);
+      locations->SetCustomSlowPathCallerSaves(OneRegInReferenceOutSaveEverythingCallerSaves());
     } else {
       // For non-Baker read barriers we have a temp-clobbering call.
     }
@@ -8368,10 +8375,7 @@ void LocationsBuilderMIPS::VisitLoadString(HLoadString* load) {
     if (load_kind == HLoadString::LoadKind::kBssEntry) {
       if (!kUseReadBarrier || kUseBakerReadBarrier) {
         // Rely on the pResolveString and marking to save everything we need.
-        RegisterSet caller_saves = RegisterSet::Empty();
-        InvokeRuntimeCallingConvention calling_convention;
-        caller_saves.Add(Location::RegisterLocation(calling_convention.GetRegisterAt(0)));
-        locations->SetCustomSlowPathCallerSaves(caller_saves);
+        locations->SetCustomSlowPathCallerSaves(OneRegInReferenceOutSaveEverythingCallerSaves());
       } else {
         // For non-Baker read barriers we have a temp-clobbering call.
       }