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assertion failure on darwin_x86_64, have to investigage

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PiperOrigin-RevId: 303346402
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Snappy Team
2020-03-27 16:35:10 +00:00
committed by Victor Costan
parent 0faf56378e
commit e19178748f
3 changed files with 21 additions and 67 deletions
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snappy.cc
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@@ -385,18 +385,11 @@ static inline char* EmitCopyAtMost64(char* op, size_t offset, size_t len) {
assert(offset < 65536);
assert(len_less_than_12 == (len < 12));
if (len_less_than_12) {
uint32 u = (len << 2) + (offset << 8);
uint32 copy1 = COPY_1_BYTE_OFFSET - (4 << 2) + ((offset >> 3) & 0xe0);
uint32 copy2 = COPY_2_BYTE_OFFSET - (1 << 2);
// It turns out that offset < 2048 is a difficult to predict branch.
// `perf record` shows this is the highest percentage of branch misses in
// benchmarks. This code produces branch free code, the data dependency
// chain that bottlenecks the throughput is so long that a few extra
// instructions are completely free (IPC << 6 because of data deps).
u += offset < 2048 ? copy1 : copy2;
LittleEndian::Store32(op, u);
op += offset < 2048 ? 2 : 3;
if (len_less_than_12 && SNAPPY_PREDICT_TRUE(offset < 2048)) {
// offset fits in 11 bits. The 3 highest go in the top of the first byte,
// and the rest go in the second byte.
*op++ = COPY_1_BYTE_OFFSET + ((len - 4) << 2) + ((offset >> 3) & 0xe0);
*op++ = offset & 0xff;
} else {
// Write 4 bytes, though we only care about 3 of them. The output buffer
// is required to have some slack, so the extra byte won't overrun it.
@@ -622,7 +615,7 @@ char* CompressFragment(const char* input,
// "literal bytes" prior to ip.
const char* base = ip;
std::pair<size_t, bool> p =
FindMatchLength(candidate + 4, ip + 4, ip_end, &data);
FindMatchLength(candidate + 4, ip + 4, ip_end);
size_t matched = 4 + p.first;
ip += matched;
size_t offset = base - candidate;
@@ -636,12 +629,12 @@ char* CompressFragment(const char* input,
if (SNAPPY_PREDICT_FALSE(ip >= ip_limit)) {
goto emit_remainder;
}
assert(LittleEndian::Load64(ip) == data);
// We are now looking for a 4-byte match again. We read
// table[Hash(ip, shift)] for that. To improve compression,
// we also update table[Hash(ip - 1, shift)] and table[Hash(ip, shift)].
table[HashBytes(LittleEndian::Load32(ip - 1), shift)] =
ip - base_ip - 1;
data = LittleEndian::Load64(ip - 1);
table[HashBytes(data, shift)] = ip - base_ip - 1;
data >>= 8;
uint32 hash = HashBytes(data, shift);
candidate = base_ip + table[hash];
table[hash] = ip - base_ip;