Make ModifyCardsAtomic 64 bit safe.
There was some logic which assumed sizeof(uintptr_t) == 4 bytes.
New method also provides a slight speedup in
FormulaEvaluationActions.EvaluateAndApplyChanges
AllocSpaceClearCards:
Before total time spent aging alloc space cards:
914ms @ 389 GC iterations
886ms @ 386 GC iterations
906ms @ 413 GC iterations
After:
865ms @ 376 GC iterations
857ms @ 386 GC iterations
826ms @ 379 GC iterations
Change-Id: Ie375b7e57c36a0257a4ffe5a1622ffb6754509c7
diff --git a/runtime/gc/accounting/card_table-inl.h b/runtime/gc/accounting/card_table-inl.h
index f0c4d0d..841f4ae 100644
--- a/runtime/gc/accounting/card_table-inl.h
+++ b/runtime/gc/accounting/card_table-inl.h
@@ -154,26 +154,30 @@
// Now we have the words, we can process words in parallel.
uintptr_t* word_cur = reinterpret_cast<uintptr_t*>(card_cur);
uintptr_t* word_end = reinterpret_cast<uintptr_t*>(card_end);
- uintptr_t expected_word;
- uintptr_t new_word;
+ union {
+ uintptr_t expected_word;
+ uint8_t expected_bytes[sizeof(uintptr_t)];
+ };
+ union {
+ uintptr_t new_word;
+ uint8_t new_bytes[sizeof(uintptr_t)];
+ };
// TODO: Parallelize.
while (word_cur < word_end) {
- while ((expected_word = *word_cur) != 0) {
- new_word =
- (visitor((expected_word >> 0) & 0xFF) << 0) |
- (visitor((expected_word >> 8) & 0xFF) << 8) |
- (visitor((expected_word >> 16) & 0xFF) << 16) |
- (visitor((expected_word >> 24) & 0xFF) << 24);
- if (new_word == expected_word) {
- // No need to do a cas.
+ while (true) {
+ expected_word = *word_cur;
+ if (LIKELY(expected_word == 0)) {
break;
}
+ for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
+ new_bytes[i] = visitor(expected_bytes[i]);
+ }
if (LIKELY(android_atomic_cas(expected_word, new_word,
reinterpret_cast<int32_t*>(word_cur)) == 0)) {
for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
- const byte expected_byte = (expected_word >> (8 * i)) & 0xFF;
- const byte new_byte = (new_word >> (8 * i)) & 0xFF;
+ const byte expected_byte = expected_bytes[i];
+ const byte new_byte = new_bytes[i];
if (expected_byte != new_byte) {
modified(reinterpret_cast<byte*>(word_cur) + i, expected_byte, new_byte);
}