[vm, compiler] Use AMOs in the RISC-V write barrier.
AMOs are more efficient than a LR/SC pair.
TEST=ci
Change-Id: I74915669bf4d13b92c04ed6ef21d61dd58df36ee
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/240142
Reviewed-by: Alexander Aprelev <aam@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>
diff --git a/runtime/vm/compiler/stub_code_compiler_riscv.cc b/runtime/vm/compiler/stub_code_compiler_riscv.cc
index e63cc88..3b3715c 100644
--- a/runtime/vm/compiler/stub_code_compiler_riscv.cc
+++ b/runtime/vm/compiler/stub_code_compiler_riscv.cc
@@ -1675,18 +1675,17 @@
__ sx(T4, Address(SP, 0 * target::kWordSize));
// Atomically clear kOldAndNotRememberedBit.
- // TODO(riscv): Use amoand instead of lr/sc.
ASSERT(target::Object::tags_offset() == 0);
__ subi(T3, A0, kHeapObjectTag);
- // T3: Untagged address of header word (lr/sc do not support offsets).
- Label retry;
- __ Bind(&retry);
- __ lr(T2, Address(T3, 0));
- __ andi(TMP2, T2, 1 << target::UntaggedObject::kOldAndNotRememberedBit);
- __ beqz(TMP2, &lost_race);
- __ andi(T2, T2, ~(1 << target::UntaggedObject::kOldAndNotRememberedBit));
- __ sc(T4, T2, Address(T3, 0));
- __ bnez(T4, &retry);
+ // T3: Untagged address of header word (amo's do not support offsets).
+ __ li(TMP2, ~(1 << target::UntaggedObject::kOldAndNotRememberedBit));
+#if XLEN == 32
+ __ amoandw(TMP2, TMP2, Address(T3, 0));
+#else
+ __ amoandd(TMP2, TMP2, Address(T3, 0));
+#endif
+ __ andi(TMP2, TMP2, 1 << target::UntaggedObject::kOldAndNotRememberedBit);
+ __ beqz(TMP2, &lost_race); // Was already clear -> lost race.
// Load the StoreBuffer block out of the thread. Then load top_ out of the
// StoreBufferBlock and add the address to the pointers_.
@@ -1738,18 +1737,18 @@
__ sx(T4, Address(SP, 0 * target::kWordSize));
// Atomically clear kOldAndNotMarkedBit.
- // TODO(riscv): Use amoand instead of lr/sc.
- Label marking_retry, marking_overflow;
+ Label marking_overflow;
ASSERT(target::Object::tags_offset() == 0);
__ subi(T3, A1, kHeapObjectTag);
- // T3: Untagged address of header word (lr/sc do not support offsets).
- __ Bind(&marking_retry);
- __ lr(T2, Address(T3, 0));
- __ andi(TMP2, T2, 1 << target::UntaggedObject::kOldAndNotMarkedBit);
- __ beqz(TMP2, &lost_race);
- __ andi(T2, T2, ~(1 << target::UntaggedObject::kOldAndNotMarkedBit));
- __ sc(T4, T2, Address(T3, 0));
- __ bnez(T4, &marking_retry);
+ // T3: Untagged address of header word (amo's do not support offsets).
+ __ li(TMP2, ~(1 << target::UntaggedObject::kOldAndNotMarkedBit));
+#if XLEN == 32
+ __ amoandw(TMP2, TMP2, Address(T3, 0));
+#else
+ __ amoandd(TMP2, TMP2, Address(T3, 0));
+#endif
+ __ andi(TMP2, TMP2, 1 << target::UntaggedObject::kOldAndNotMarkedBit);
+ __ beqz(TMP2, &lost_race); // Was already clear -> lost race.
__ LoadFromOffset(T4, THR, target::Thread::marking_stack_block_offset());
__ LoadFromOffset(T2, T4, target::MarkingStackBlock::top_offset(),
