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[huf] Add generic C versions of the fast decoding loops

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Add generic C versions of the fast decoding loops to serve architectures
that don't have an assembly implementation. Also allow selecting the C
decoding loop over the assembly decoding loop through a zstd
decompression parameter `ZSTD_d_disableHuffmanAssembly`.

I benchmarked on my Intel i9-9900K and my Macbook Air with an M1 processor.
The benchmark command forces zstd to compress without any matches, using
only literals compression, and measures only Huffman decompression speed:

```
zstd -b1e1 --compress-literals --zstd=tlen=131072 silesia.tar
```

The new fast decoding loops outperform the previous implementation uniformly,
but don't beat the x86-64 assembly. Additionally, the fast C decoding loops suffer
from the same stability problems that we've seen in the past, where the assembly
version doesn't. So even though clang gets close to assembly on x86-64, it still
has stability issues.

| Arch    | Function       | Compiler     | Default (MB/s) | Assembly (MB/s) | Fast (MB/s) |
|---------|----------------|--------------|----------------|-----------------|-------------|
| x86-64  | decompress 4X1 | gcc-12.2.0   |         1029.6 |          1308.1 |      1208.1 |
| x86-64  | decompress 4X1 | clang-14.0.6 |         1019.3 |          1305.6 |      1276.3 |
| x86-64  | decompress 4X2 | gcc-12.2.0   |         1348.5 |          1657.0 |      1374.1 |
| x86-64  | decompress 4X2 | clang-14.0.6 |         1027.6 |          1659.9 |      1468.1 |
| aarch64 | decompress 4X1 | clang-12.0.5 |         1081.0 |             N/A |      1234.9 |
| aarch64 | decompress 4X2 | clang-12.0.5 |         1270.0 |             N/A |      1516.6 |
This commit is contained in:
Nick Terrell
2023-01-25 13:47:51 -08:00
committed by Nick Terrell
parent f3255bfeff
commit 8957fef554
13 changed files with 448 additions and 91 deletions
Download Patch File Download Diff File Expand all files Collapse all files
tests/zstreamtest.c
+14 -1
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@@ -2889,6 +2889,9 @@ static int fuzzerTests_newAPI(U32 seed, int nbTests, int startTest,
CHECK(badParameters(zc, savedParams), "CCtx params are wrong");
/* multi - fragments decompression test */
if (FUZ_rand(&lseed) & 1) {
CHECK_Z(ZSTD_DCtx_reset(zd, ZSTD_reset_session_and_parameters));
}
if (!dictSize /* don't reset if dictionary : could be different */ && (FUZ_rand(&lseed) & 1)) {
DISPLAYLEVEL(5, "resetting DCtx (dict:%p) \n", (void const*)dict);
CHECK_Z( ZSTD_resetDStream(zd) );
@@ -2897,6 +2900,9 @@ static int fuzzerTests_newAPI(U32 seed, int nbTests, int startTest,
DISPLAYLEVEL(5, "using dictionary of size %zu \n", dictSize);
CHECK_Z( ZSTD_initDStream_usingDict(zd, dict, dictSize) );
}
if (FUZ_rand(&lseed) & 1) {
CHECK_Z(ZSTD_DCtx_setParameter(zd, ZSTD_d_disableHuffmanAssembly, FUZ_rand(&lseed) & 1));
}
{ size_t decompressionResult = 1;
ZSTD_inBuffer inBuff = { cBuffer, cSize, 0 };
ZSTD_outBuffer outBuff= { dstBuffer, dstBufferSize, 0 };
@@ -2938,7 +2944,14 @@ static int fuzzerTests_newAPI(U32 seed, int nbTests, int startTest,
} }
/* try decompression on noisy data */
CHECK_Z( ZSTD_initDStream(zd_noise) ); /* note : no dictionary */
if (FUZ_rand(&lseed) & 1) {
CHECK_Z(ZSTD_DCtx_reset(zd_noise, ZSTD_reset_session_and_parameters));
} else {
CHECK_Z(ZSTD_DCtx_reset(zd_noise, ZSTD_reset_session_only));
}
if (FUZ_rand(&lseed) & 1) {
CHECK_Z(ZSTD_DCtx_setParameter(zd_noise, ZSTD_d_disableHuffmanAssembly, FUZ_rand(&lseed) & 1));
}
{ ZSTD_inBuffer inBuff = { cBuffer, cSize, 0 };
ZSTD_outBuffer outBuff= { dstBuffer, dstBufferSize, 0 };
while (outBuff.pos < dstBufferSize) {