Fix art's System.arraycopy now bionic doesn't have _memmove_words.
Change-Id: Ib4fc502eda7f5902e0cbe50ed9df892314a49017
diff --git a/src/native/java_lang_System.cc b/src/native/java_lang_System.cc
index 79614ae..5572623 100644
--- a/src/native/java_lang_System.cc
+++ b/src/native/java_lang_System.cc
@@ -48,61 +48,123 @@
* appropriately for the element type, and that n is a multiple of the
* element size.
*/
-#ifdef __BIONIC__
-#define HAVE_MEMMOVE_WORDS
-#endif
-#ifdef HAVE_MEMMOVE_WORDS
-extern "C" void _memmove_words(void* dst, const void* src, size_t n);
-#define move16 _memmove_words
-#define move32 _memmove_words
-#else
-static void move16(void* dst, const void* src, size_t n) {
+/*
+ * Works like memmove(), except:
+ * - if all arguments are at least 32-bit aligned, we guarantee that we
+ * will use operations that preserve atomicity of 32-bit values
+ * - if not, we guarantee atomicity of 16-bit values
+ *
+ * If all three arguments are not at least 16-bit aligned, the behavior
+ * of this function is undefined. (We could remove this restriction by
+ * testing for unaligned values and punting to memmove(), but that's
+ * not currently useful.)
+ *
+ * TODO: add loop for 64-bit alignment
+ * TODO: use __builtin_prefetch
+ * TODO: write ARM/MIPS/x86 optimized versions
+ */
+void MemmoveWords(void* dst, const void* src, size_t n) {
DCHECK_EQ((((uintptr_t) dst | (uintptr_t) src | n) & 0x01), 0U);
- uint16_t* d = reinterpret_cast<uint16_t*>(dst);
- const uint16_t* s = reinterpret_cast<const uint16_t*>(src);
+ char* d = reinterpret_cast<char*>(dst);
+ const char* s = reinterpret_cast<const char*>(src);
+ size_t copyCount;
- n /= sizeof(uint16_t);
+ // If the source and destination pointers are the same, this is
+ // an expensive no-op. Testing for an empty move now allows us
+ // to skip a check later.
+ if (n == 0 || d == s) {
+ return;
+ }
- if (d < s) {
- // Copy forwards.
- while (n--) {
- *d++ = *s++;
+ // Determine if the source and destination buffers will overlap if
+ // we copy data forward (i.e. *dst++ = *src++).
+ //
+ // It's okay if the destination buffer starts before the source and
+ // there is some overlap, because the reader is always ahead of the
+ // writer.
+ if (LIKELY((d < s) || ((size_t)(d - s) >= n))) {
+ // Copy forward. We prefer 32-bit loads and stores even for 16-bit
+ // data, so sort that out.
+ if (((reinterpret_cast<uintptr_t>(d) | reinterpret_cast<uintptr_t>(s)) & 0x03) != 0) {
+ // Not 32-bit aligned. Two possibilities:
+ // (1) Congruent, we can align to 32-bit by copying one 16-bit val
+ // (2) Non-congruent, we can do one of:
+ // a. copy whole buffer as a series of 16-bit values
+ // b. load/store 32 bits, using shifts to ensure alignment
+ // c. just copy the as 32-bit values and assume the CPU
+ // will do a reasonable job
+ //
+ // We're currently using (a), which is suboptimal.
+ if (((reinterpret_cast<uintptr_t>(d) ^ reinterpret_cast<uintptr_t>(s)) & 0x03) != 0) {
+ copyCount = n;
+ } else {
+ copyCount = 2;
+ }
+ n -= copyCount;
+ copyCount /= sizeof(uint16_t);
+
+ while (copyCount--) {
+ *reinterpret_cast<uint16_t*>(d) = *reinterpret_cast<const uint16_t*>(s);
+ d += sizeof(uint16_t);
+ s += sizeof(uint16_t);
+ }
+ }
+
+ // Copy 32-bit aligned words.
+ copyCount = n / sizeof(uint32_t);
+ while (copyCount--) {
+ *reinterpret_cast<uint32_t*>(d) = *reinterpret_cast<const uint32_t*>(s);
+ d += sizeof(uint32_t);
+ s += sizeof(uint32_t);
+ }
+
+ // Check for leftovers. Either we finished exactly, or we have one remaining 16-bit chunk.
+ if ((n & 0x02) != 0) {
+ *(uint16_t*)d = *(uint16_t*)s;
}
} else {
- // Copy backwards.
+ // Copy backward, starting at the end.
d += n;
s += n;
- while (n--) {
- *--d = *--s;
+
+ if (((reinterpret_cast<uintptr_t>(d) | reinterpret_cast<uintptr_t>(s)) & 0x03) != 0) {
+ // try for 32-bit alignment.
+ if (((reinterpret_cast<uintptr_t>(d) ^ reinterpret_cast<uintptr_t>(s)) & 0x03) != 0) {
+ copyCount = n;
+ } else {
+ copyCount = 2;
+ }
+ n -= copyCount;
+ copyCount /= sizeof(uint16_t);
+
+ while (copyCount--) {
+ d -= sizeof(uint16_t);
+ s -= sizeof(uint16_t);
+ *reinterpret_cast<uint16_t*>(d) = *reinterpret_cast<const uint16_t*>(s);
+ }
+ }
+
+ // Copy 32-bit aligned words.
+ copyCount = n / sizeof(uint32_t);
+ while (copyCount--) {
+ d -= sizeof(uint32_t);
+ s -= sizeof(uint32_t);
+ *reinterpret_cast<uint32_t*>(d) = *reinterpret_cast<const uint32_t*>(s);
+ }
+
+ // Copy leftovers.
+ if ((n & 0x02) != 0) {
+ d -= sizeof(uint16_t);
+ s -= sizeof(uint16_t);
+ *reinterpret_cast<uint16_t*>(d) = *reinterpret_cast<const uint16_t*>(s);
}
}
}
-static void move32(void* dst, const void* src, size_t n) {
- DCHECK_EQ((((uintptr_t) dst | (uintptr_t) src | n) & 0x03), 0U);
-
- uint32_t* d = reinterpret_cast<uint32_t*>(dst);
- const uint32_t* s = reinterpret_cast<const uint32_t*>(src);
-
- n /= sizeof(uint32_t);
-
- if (d < s) {
- // Copy forwards.
- while (n--) {
- *d++ = *s++;
- }
- } else {
- // Copy backwards.
- d += n;
- s += n;
- while (n--) {
- *--d = *--s;
- }
- }
-}
-#endif // HAVE_MEMMOVE_WORDS
+#define move16 MemmoveWords
+#define move32 MemmoveWords
namespace art {