Hi. I've written a patch draft that replaces zlib with the zstd compression algorithm ([1]) in LTO. I'm also sending statistics that are collected for couple of quite big C++ source files. Observation I did:
- LTO stream compression takes 3-4% of LGEN compile time - zstd in default compression level (3) generated slighly smaller LTO elf files - zstd compression is 4-8x faster - decompression is quite negligible, but for a bigger project (godot) I can reduction from 1.37 to 0.53 seconds - ZSTD API is much simpler to use Suggestion based on the observation: - I would suggest to make zstd optional (--enable-zstd) and one would use #include <zstd> + -lzstd - I like the default level as we want to mainly speed up LTO compilation - we can provide an option to control algorithm (-flto-compression-algorithm), similarly to -flto-compression-level - we can discuss possible compression of LTO bytecode that is distributed between WPA stage and individual LTRANS phases. Thoughts? Thanks, Martin [1] https://github.com/facebook/zstd
>From 4939e90b2a8051128b7b2b0214a5fad5183f3bca Mon Sep 17 00:00:00 2001
From: Martin Liska <mli...@suse.cz>
Date: Wed, 19 Jun 2019 09:40:35 +0200
Subject: [PATCH] Replace zlib with zstd.
---
gcc/Makefile.in | 2 +-
gcc/common.opt | 2 +-
gcc/lto-compress.c | 161 ++++++++-------------------------------------
gcc/timevar.def | 4 +-
4 files changed, 33 insertions(+), 136 deletions(-)
diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index d9e0885b96b..8aedcccb717 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -373,7 +373,7 @@ OUTPUT_OPTION = -o $@
# This is where we get zlib from. zlibdir is -L../zlib and zlibinc is
# -I../zlib, unless we were configured with --with-system-zlib, in which
# case both are empty.
-ZLIB = @zlibdir@ -lz
+ZLIB = @zlibdir@ -lzstd -lz
ZLIBINC = @zlibinc@
# How to find GMP
diff --git a/gcc/common.opt b/gcc/common.opt
index a1544d06824..f15e21914f3 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1888,7 +1888,7 @@ Specify the algorithm to partition symbols and vars at linktime.
; The initial value of -1 comes from Z_DEFAULT_COMPRESSION in zlib.h.
flto-compression-level=
-Common Joined RejectNegative UInteger Var(flag_lto_compression_level) Init(-1) IntegerRange(0, 9)
+Common Joined RejectNegative UInteger Var(flag_lto_compression_level) Init(-1) IntegerRange(0, 1111)
-flto-compression-level=<number> Use zlib compression level <number> for IL.
flto-odr-type-merging
diff --git a/gcc/lto-compress.c b/gcc/lto-compress.c
index 3287178f257..b24f30f956e 100644
--- a/gcc/lto-compress.c
+++ b/gcc/lto-compress.c
@@ -27,13 +27,9 @@ along with GCC; see the file COPYING3. If not see
#include "gimple.h"
#include "cgraph.h"
#include "lto-streamer.h"
-/* zlib.h includes other system headers. Those headers may test feature
- test macros. config.h may define feature test macros. For this reason,
- zlib.h needs to be included after, rather than before, config.h and
- system.h. */
-#include <zlib.h>
#include "lto-compress.h"
#include "timevar.h"
+#include <zstd.h>
/* Compression stream structure, holds the flush callback and opaque token,
the buffered data, and a note of whether compressing or uncompressing. */
@@ -48,45 +44,23 @@ struct lto_compression_stream
bool is_compression;
};
-/* Overall compression constants for zlib. */
-
-static const size_t Z_BUFFER_LENGTH = 4096;
static const size_t MIN_STREAM_ALLOCATION = 1024;
-/* For zlib, allocate SIZE count of ITEMS and return the address, OPAQUE
- is unused. */
-
-static void *
-lto_zalloc (void *opaque, unsigned items, unsigned size)
-{
- gcc_assert (opaque == Z_NULL);
- return xmalloc (items * size);
-}
-
-/* For zlib, free memory at ADDRESS, OPAQUE is unused. */
-
-static void
-lto_zfree (void *opaque, void *address)
-{
- gcc_assert (opaque == Z_NULL);
- free (address);
-}
-
-/* Return a zlib compression level that zlib will not reject. Normalizes
+/* Return a zstd compression level that zstd will not reject. Normalizes
the compression level from the command line flag, clamping non-default
values to the appropriate end of their valid range. */
static int
-lto_normalized_zlib_level (void)
+lto_normalized_zstd_level (void)
{
int level = flag_lto_compression_level;
- if (level != Z_DEFAULT_COMPRESSION)
+ if (level != ZSTD_CLEVEL_DEFAULT)
{
- if (level < Z_NO_COMPRESSION)
- level = Z_NO_COMPRESSION;
- else if (level > Z_BEST_COMPRESSION)
- level = Z_BEST_COMPRESSION;
+ if (level < 1)
+ level = 1;
+ else if (level > ZSTD_maxCLevel ())
+ level = ZSTD_maxCLevel ();
}
return level;
@@ -169,57 +143,19 @@ void
lto_end_compression (struct lto_compression_stream *stream)
{
unsigned char *cursor = (unsigned char *) stream->buffer;
- size_t remaining = stream->bytes;
- const size_t outbuf_length = Z_BUFFER_LENGTH;
- unsigned char *outbuf = (unsigned char *) xmalloc (outbuf_length);
- z_stream out_stream;
- size_t compressed_bytes = 0;
- int status;
-
- gcc_assert (stream->is_compression);
+ size_t size = stream->bytes;
timevar_push (TV_IPA_LTO_COMPRESS);
+ size_t const outbuf_length = ZSTD_compressBound (size);
+ char *outbuf = (char *) xmalloc (outbuf_length);
- out_stream.next_out = outbuf;
- out_stream.avail_out = outbuf_length;
- out_stream.next_in = cursor;
- out_stream.avail_in = remaining;
- out_stream.zalloc = lto_zalloc;
- out_stream.zfree = lto_zfree;
- out_stream.opaque = Z_NULL;
+ size_t const csize = ZSTD_compress (outbuf, outbuf_length, cursor, size,
+ lto_normalized_zstd_level ());
- status = deflateInit (&out_stream, lto_normalized_zlib_level ());
- if (status != Z_OK)
- internal_error ("compressed stream: %s", zError (status));
+ if (ZSTD_isError (csize))
+ internal_error ("compressed stream: %s", ZSTD_getErrorName (csize));
- do
- {
- size_t in_bytes, out_bytes;
-
- status = deflate (&out_stream, Z_FINISH);
- if (status != Z_OK && status != Z_STREAM_END)
- internal_error ("compressed stream: %s", zError (status));
-
- in_bytes = remaining - out_stream.avail_in;
- out_bytes = outbuf_length - out_stream.avail_out;
-
- stream->callback ((const char *) outbuf, out_bytes, stream->opaque);
- lto_stats.num_compressed_il_bytes += out_bytes;
- compressed_bytes += out_bytes;
-
- cursor += in_bytes;
- remaining -= in_bytes;
-
- out_stream.next_out = outbuf;
- out_stream.avail_out = outbuf_length;
- out_stream.next_in = cursor;
- out_stream.avail_in = remaining;
- }
- while (status != Z_STREAM_END);
-
- status = deflateEnd (&out_stream);
- if (status != Z_OK)
- internal_error ("compressed stream: %s", zError (status));
+ stream->callback (outbuf, csize, NULL);
lto_destroy_compression_stream (stream);
free (outbuf);
@@ -258,61 +194,22 @@ void
lto_end_uncompression (struct lto_compression_stream *stream)
{
unsigned char *cursor = (unsigned char *) stream->buffer;
- size_t remaining = stream->bytes;
- const size_t outbuf_length = Z_BUFFER_LENGTH;
- unsigned char *outbuf = (unsigned char *) xmalloc (outbuf_length);
- size_t uncompressed_bytes = 0;
+ size_t size = stream->bytes;
- gcc_assert (!stream->is_compression);
timevar_push (TV_IPA_LTO_DECOMPRESS);
+ unsigned long long const rsize = ZSTD_getFrameContentSize (cursor, size);
+ if (rsize == ZSTD_CONTENTSIZE_ERROR)
+ internal_error ("not compressed by zstd");
+ else if (rsize == ZSTD_CONTENTSIZE_UNKNOWN)
+ internal_error ("original size unknown");
- while (remaining > 0)
- {
- z_stream in_stream;
- size_t out_bytes;
- int status;
-
- in_stream.next_out = outbuf;
- in_stream.avail_out = outbuf_length;
- in_stream.next_in = cursor;
- in_stream.avail_in = remaining;
- in_stream.zalloc = lto_zalloc;
- in_stream.zfree = lto_zfree;
- in_stream.opaque = Z_NULL;
-
- status = inflateInit (&in_stream);
- if (status != Z_OK)
- internal_error ("compressed stream: %s", zError (status));
-
- do
- {
- size_t in_bytes;
-
- status = inflate (&in_stream, Z_SYNC_FLUSH);
- if (status != Z_OK && status != Z_STREAM_END)
- internal_error ("compressed stream: %s", zError (status));
-
- in_bytes = remaining - in_stream.avail_in;
- out_bytes = outbuf_length - in_stream.avail_out;
-
- stream->callback ((const char *) outbuf, out_bytes, stream->opaque);
- lto_stats.num_uncompressed_il_bytes += out_bytes;
- uncompressed_bytes += out_bytes;
-
- cursor += in_bytes;
- remaining -= in_bytes;
-
- in_stream.next_out = outbuf;
- in_stream.avail_out = outbuf_length;
- in_stream.next_in = cursor;
- in_stream.avail_in = remaining;
- }
- while (!(status == Z_STREAM_END && out_bytes == 0));
-
- status = inflateEnd (&in_stream);
- if (status != Z_OK)
- internal_error ("compressed stream: %s", zError (status));
- }
+ char *outbuf = (char *) xmalloc (rsize);
+ size_t const dsize = ZSTD_decompress (outbuf, rsize, cursor, size);
+
+ if (ZSTD_isError (dsize))
+ internal_error ("decompressed stream: %s", ZSTD_getErrorName (dsize));
+
+ stream->callback (outbuf, dsize, stream->opaque);
lto_destroy_compression_stream (stream);
free (outbuf);
diff --git a/gcc/timevar.def b/gcc/timevar.def
index 13cb470b688..626ce493b76 100644
--- a/gcc/timevar.def
+++ b/gcc/timevar.def
@@ -78,8 +78,8 @@ DEFTIMEVAR (TV_IPA_INLINING , "ipa inlining heuristics")
DEFTIMEVAR (TV_IPA_FNSPLIT , "ipa function splitting")
DEFTIMEVAR (TV_IPA_COMDATS , "ipa comdats")
DEFTIMEVAR (TV_IPA_OPT , "ipa various optimizations")
-DEFTIMEVAR (TV_IPA_LTO_DECOMPRESS , "lto stream inflate")
-DEFTIMEVAR (TV_IPA_LTO_COMPRESS , "lto stream deflate")
+DEFTIMEVAR (TV_IPA_LTO_DECOMPRESS , "lto stream decompression")
+DEFTIMEVAR (TV_IPA_LTO_COMPRESS , "lto stream compression")
DEFTIMEVAR (TV_IPA_LTO_OUTPUT , "lto stream output")
DEFTIMEVAR (TV_IPA_LTO_GIMPLE_IN , "ipa lto gimple in")
DEFTIMEVAR (TV_IPA_LTO_GIMPLE_OUT , "ipa lto gimple out")
--
2.21.0
zstd-vs-zlib.ods
Description: application/vnd.oasis.opendocument.spreadsheet
