Use entrypoint switching on x86 & x86-64 for GC root read barriers.
For consistency reason (with the ARM and ARM64 implementations),
check the read barrier marking entrypoint
(`Thread::Current()->pReadBarrierMarkReg ## root.reg()`)
instead of `Thread::Current()->GetIsGcMarking()` to decide whether
to mark a GC root.
This change should have no impact on the performance or the
size of the generated code.
Test: m test-art-host
Bug: 32638713
Change-Id: Ifd71312992fdfd6067447cccb7d95860f3771b57
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index 20cdae3..e664089 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -624,6 +624,10 @@
// probably still be a from-space reference (unless it gets updated by
// another thread, or if another thread installed another object
// reference (different from `ref`) in `obj.field`).
+//
+// If `entrypoint` is a valid location it is assumed to already be
+// holding the entrypoint. The case where the entrypoint is passed in
+// is for the GcRoot read barrier.
class ReadBarrierMarkSlowPathARM : public SlowPathCodeARM {
public:
ReadBarrierMarkSlowPathARM(HInstruction* instruction,
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index 598be47..017dd36 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -619,8 +619,10 @@
// probably still be a from-space reference (unless it gets updated by
// another thread, or if another thread installed another object
// reference (different from `ref`) in `obj.field`).
-// If entrypoint is a valid location it is assumed to already be holding the entrypoint. The case
-// where the entrypoint is passed in is for the GcRoot read barrier.
+//
+// If `entrypoint` is a valid location it is assumed to already be
+// holding the entrypoint. The case where the entrypoint is passed in
+// is for the GcRoot read barrier.
class ReadBarrierMarkSlowPathARM64 : public SlowPathCodeARM64 {
public:
ReadBarrierMarkSlowPathARM64(HInstruction* instruction,
diff --git a/compiler/optimizing/code_generator_x86.cc b/compiler/optimizing/code_generator_x86.cc
index 137b554..9276616 100644
--- a/compiler/optimizing/code_generator_x86.cc
+++ b/compiler/optimizing/code_generator_x86.cc
@@ -7136,9 +7136,10 @@
// Fast path implementation of art::ReadBarrier::BarrierForRoot when
// Baker's read barrier are used:
//
- // root = *address;
- // if (Thread::Current()->GetIsGcMarking()) {
- // root = ReadBarrier::Mark(root)
+ // root = obj.field;
+ // temp = Thread::Current()->pReadBarrierMarkReg ## root.reg()
+ // if (temp != null) {
+ // root = temp(root)
// }
// /* GcRoot<mirror::Object> */ root = *address
@@ -7159,8 +7160,11 @@
instruction, root, /* unpoison_ref_before_marking */ false);
codegen_->AddSlowPath(slow_path);
- __ fs()->cmpl(Address::Absolute(Thread::IsGcMarkingOffset<kX86PointerSize>().Int32Value()),
- Immediate(0));
+ // Test the entrypoint (`Thread::Current()->pReadBarrierMarkReg ## root.reg()`).
+ const int32_t entry_point_offset =
+ CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kX86PointerSize>(root.reg());
+ __ fs()->cmpl(Address::Absolute(entry_point_offset), Immediate(0));
+ // The entrypoint is null when the GC is not marking.
__ j(kNotEqual, slow_path->GetEntryLabel());
__ Bind(slow_path->GetExitLabel());
} else {
diff --git a/compiler/optimizing/code_generator_x86_64.cc b/compiler/optimizing/code_generator_x86_64.cc
index c5367ce..c3ed416 100644
--- a/compiler/optimizing/code_generator_x86_64.cc
+++ b/compiler/optimizing/code_generator_x86_64.cc
@@ -6501,9 +6501,10 @@
// Fast path implementation of art::ReadBarrier::BarrierForRoot when
// Baker's read barrier are used:
//
- // root = *address;
- // if (Thread::Current()->GetIsGcMarking()) {
- // root = ReadBarrier::Mark(root)
+ // root = obj.field;
+ // temp = Thread::Current()->pReadBarrierMarkReg ## root.reg()
+ // if (temp != null) {
+ // root = temp(root)
// }
// /* GcRoot<mirror::Object> */ root = *address
@@ -6524,9 +6525,11 @@
instruction, root, /* unpoison_ref_before_marking */ false);
codegen_->AddSlowPath(slow_path);
- __ gs()->cmpl(Address::Absolute(Thread::IsGcMarkingOffset<kX86_64PointerSize>().Int32Value(),
- /* no_rip */ true),
- Immediate(0));
+ // Test the `Thread::Current()->pReadBarrierMarkReg ## root.reg()` entrypoint.
+ const int32_t entry_point_offset =
+ CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kX86_64PointerSize>(root.reg());
+ __ gs()->cmpl(Address::Absolute(entry_point_offset, /* no_rip */ true), Immediate(0));
+ // The entrypoint is null when the GC is not marking.
__ j(kNotEqual, slow_path->GetEntryLabel());
__ Bind(slow_path->GetExitLabel());
} else {
