ARM read barrier support for concurrent GC in Optimizing.

This first implementation uses slow paths to instrument heap
reference loads and GC root loads for the concurrent copying
collector, respectively calling the artReadBarrierSlow and
artReadBarrierForRootSlow runtime entry points.

Notes:
- This implementation does not instrument HInvokeVirtual
  nor HInvokeInterface instructions (for class reference
  loads), as the corresponding read barriers are not stricly
  required with the current concurrent copying collector.
- Intrinsics which may eventually call (on slow path) are
  disabled when read barriers are enabled, as the current
  slow path infrastructure does not support this case.
- When read barriers are enabled, the code generated for a
  HArraySet instruction always go into the array set slow
  path for object arrays (delegating the operation to the
  runtime), as we are lacking a mechanism to keep a
  temporary register live accross a runtime call (needed for
  the instrumentation of type checking code, which requires
  two successive read barriers).

Bug: 12687968
Change-Id: I92e8db414d029f952c07f3d3a98069e46dfdbc2a

1 files changed, 5 insertions, 4 deletions

diff --git a/compiler/optimizing/optimizing_compiler.cc b/compiler/optimizing/optimizing_compiler.cc
index 27ee47296c..2204921c53 100644
--- a/compiler/optimizing/optimizing_compiler.cc
+++ b/compiler/optimizing/optimizing_compiler.cc
@@ -383,10 +383,11 @@ static bool IsInstructionSetSupported(InstructionSet instruction_set) {
       || instruction_set == kX86_64;
 }
 
-// Read barrier are supported only on x86 and x86-64 at the moment.
+// Read barrier are supported only on ARM, x86 and x86-64 at the moment.
 // TODO: Add support for other architectures and remove this function
 static bool InstructionSetSupportsReadBarrier(InstructionSet instruction_set) {
-  return instruction_set == kX86
+  return instruction_set == kThumb2
+      || instruction_set == kX86
       || instruction_set == kX86_64;
 }
 
@@ -668,8 +669,8 @@ CodeGenerator* OptimizingCompiler::TryCompile(ArenaAllocator* arena,
   CompilerDriver* compiler_driver = GetCompilerDriver();
   InstructionSet instruction_set = compiler_driver->GetInstructionSet();
 
-  // Always use the thumb2 assembler: some runtime functionality (like implicit stack
-  // overflow checks) assume thumb2.
+  // Always use the Thumb-2 assembler: some runtime functionality
+  // (like implicit stack overflow checks) assume Thumb-2.
   if (instruction_set == kArm) {
     instruction_set = kThumb2;
   }