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Merge pull request #135 from JunHe77:remove_extra 

PiperOrigin-RevId: 390767998
This commit is contained in:
Victor Costan 2021-08-14 08:15:44 +00:00
parent 5c87bc61b6 d643b9a988
commit b9c9a989b2
1 changed files with 9 additions and 0 deletions
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snappy.cc
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@ -1112,6 +1112,15 @@ std::pair<const uint8_t*, ptrdiff_t> DecompressBranchless(
// ip points just past the tag and we are touching at maximum kSlopBytes
// in an iteration.
size_t tag = ip[-1];
#if defined(__clang__) && defined(__aarch64__)
// Workaround for https://bugs.llvm.org/show_bug.cgi?id=51317
// when loading 1 byte, clang for aarch64 doesn't realize that it(ldrb)
// comes with free zero-extension, so clang generates another
// 'and xn, xm, 0xff' before it use that as the offset. This 'and' is
// redundant and can be removed by adding this dummy asm, which gives
// clang a hint that we're doing the zero-extension at the load.
asm("" ::"r"(tag));
#endif
do {
// The throughput is limited by instructions, unrolling the inner loop
// twice reduces the amount of instructions checking limits and also