Switch from XXH64 to XXH3 for checksums (ccache#657)

The latter promises better performance and supports automatic use of vector
instructions where appropriate.

LICENSE.adoc

@@ -268,14 +268,15 @@ SOFTWARE.
 -------------------------------------------------------------------------------
 
 
-src/third_party/xxhash.[hc]
+src/third_party/xxh(ash|_x86dispatch).[hc]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-xxHash - Extremely Fast Hash algorithm. Copied from xxHash v0.6.5 downloaded
+xxHash - Extremely Fast Hash algorithm. Copied from xxHash v0.8.0 downloaded
 from <https://github.com/Cyan4973/xxHash/releases>.
 
 -------------------------------------------------------------------------------
-   Copyright (C) 2012-2016, Yann Collet.
+   Copyright (c) 2012-2020 Yann Collet
+   All rights reserved.
 
    BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)
 
@@ -301,9 +302,6 @@ from <https://github.com/Cyan4973/xxHash/releases>.
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
-   You can contact the author at :
-   - xxHash source repository : https://github.com/Cyan4973/xxHash
 -------------------------------------------------------------------------------
 
 

doc/MANUAL.adoc

@@ -170,7 +170,7 @@ Options for scripting or debugging
 
 *`--checksum-file`* _PATH_::
 
-    Print the checksum (64 bit XXH64) of the file at _PATH_.
+    Print the checksum (64 bit XXH3) of the file at _PATH_.
 
 *`--dump-manifest`* _PATH_::
 
@@ -998,7 +998,7 @@ compilation and then using the hash sum to identify the cached output. ccache
 uses BLAKE3, a very fast cryptographic hash algorithm, for the hashing. On a
 cache hit, ccache is able to supply all of the correct compiler outputs
 (including all warnings, dependency file, etc) from the cache. Data stored in
-the cache is checksummed with XXH64, an extremely fast non-cryptographic
+the cache is checksummed with XXH3, an extremely fast non-cryptographic
 algorithm, to detect corruption.
 
 ccache has two ways of gathering information used to look up results in the

doc/NEWS.adoc

@@ -16,7 +16,7 @@ High-level summary of changes (work in progress)
 
 - BLAKE3 is now used instead of MD4 for hashing input.
 
-- Added checksumming of result files using XXH64 to detect data corruption.
+- Added checksumming of result files using XXH3 to detect data corruption.
 
 - Made the hard link mode less error prone.
 

src/Checksum.hpp

@@ -20,7 +20,11 @@
 
 #include "system.hpp"
 
-#include "third_party/xxhash.h"
+#ifdef USE_XXH_DISPATCH
+#  include "third_party/xxh_x86dispatch.h"
+#else
+#  include "third_party/xxhash.h"
+#endif
 
 class Checksum
 {
@@ -33,33 +37,33 @@ class Checksum
   uint64_t digest() const;
 
 private:
-  XXH64_state_t* m_state;
+  XXH3_state_t* m_state;
 };
 
-inline Checksum::Checksum() : m_state(XXH64_createState())
+inline Checksum::Checksum() : m_state(XXH3_createState())
 {
   reset();
 }
 
 inline Checksum::~Checksum()
 {
-  XXH64_freeState(m_state);
+  XXH3_freeState(m_state);
 }
 
 inline void
 Checksum::reset()
 {
-  XXH64_reset(m_state, 0);
+  XXH3_64bits_reset(m_state);
 }
 
 inline void
 Checksum::update(const void* data, size_t length)
 {
-  XXH64_update(m_state, data, length);
+  XXH3_64bits_update(m_state, data, length);
 }
 
 inline uint64_t
 Checksum::digest() const
 {
-  return XXH64_digest(m_state);
+  return XXH3_64bits_digest(m_state);
 }

src/Manifest.cpp

@@ -69,7 +69,7 @@
 // <include_index> ::= uint32_t
 // <name>          ::= Digest::size() bytes
 // <epilogue>      ::= <checksum>
-// <checksum>      ::= uint64_t ; XXH64 of content bytes
+// <checksum>      ::= uint64_t ; XXH3 of content bytes
 //
 // Sketch of concrete layout:
 

src/Result.cpp

@@ -61,7 +61,7 @@
 // <raw_file_marker>      ::= 1 (uint8_t)
 // <file_len>             ::= uint64_t
 // <epilogue>             ::= <checksum>
-// <checksum>             ::= uint64_t ; XXH64 of content bytes
+// <checksum>             ::= uint64_t ; XXH3 of content bytes
 //
 // Sketch of concrete layout:
 //

src/ccache.cpp

@@ -128,7 +128,7 @@ Common options:
     -V, --version              print version and copyright information
 
 Options for scripting or debugging:
-        --checksum-file PATH   print the checksum (64 bit XXH64) of the file at
+        --checksum-file PATH   print the checksum (64 bit XXH3) of the file at
                                PATH
         --dump-manifest PATH   dump manifest file at PATH in text format
         --dump-result PATH     dump result file at PATH in text format

src/third_party/CMakeLists.txt

@@ -10,6 +10,29 @@ if(ENABLE_TRACING)
   target_sources(third_party_lib PRIVATE minitrace.c)
 endif()
 
+set(xxhdispatchtest [=[
+#include "xxh_x86dispatch.c"
+
+int main()
+{
+  XXH3_64bits_dispatch("foo", 3);
+  return 1;
+}
+]=])
+
+file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/xxhdispatchtest.c" "${xxhdispatchtest}")
+
+try_compile(USE_XXH_DISPATCH ${CMAKE_CURRENT_BINARY_DIR}
+  "${CMAKE_CURRENT_BINARY_DIR}/xxhdispatchtest.c"
+  CMAKE_FLAGS "-DINCLUDE_DIRECTORIES=${CMAKE_CURRENT_SOURCE_DIR}"
+  COMPILE_DEFINITIONS "-DXXH_STATIC_LINKING_ONLY")
+
+target_compile_definitions(third_party_lib INTERFACE "-DXXH_STATIC_LINKING_ONLY")
+if(USE_XXH_DISPATCH)
+  target_sources(third_party_lib PRIVATE xxh_x86dispatch.c)
+  target_compile_definitions(third_party_lib INTERFACE "-DUSE_XXH_DISPATCH")
+endif()
+
 # Treat third party headers as system files (no warning for those headers).
 target_include_directories(
   third_party_lib