Geometry Nodes: use xxhash for compute context hash

Previously, md5 was used which is significantly slower. In almost all cases
this does not have a significant performance impact in practice. However,
it's possible to build geometry nodes setups that become a few percent
faster ( by combining lots of cheap node groups). Using xxhash instead of
md5 should never be slower.

Pull Request: https://projects.blender.org/blender/blender/pulls/120225

source/blender/blenlib/CMakeLists.txt

@@ -401,6 +401,7 @@ set(SRC
 set(LIB
   PUBLIC bf::dna
   PRIVATE bf::extern::fmtlib
+  PRIVATE bf::extern::xxhash
   bf_intern_eigen
   PRIVATE bf::intern::guardedalloc
   extern_wcwidth

source/blender/blenlib/intern/compute_context.cc

@@ -3,8 +3,9 @@
  * SPDX-License-Identifier: GPL-2.0-or-later */
 
 #include "BLI_compute_context.hh"
-#include "BLI_hash_md5.hh"
+
 #include <sstream>
+#include <xxhash.h>
 
 namespace blender {
 
@@ -15,7 +16,9 @@ void ComputeContextHash::mix_in(const void *data, int64_t len)
   memcpy(buffer, this, HashSizeInBytes);
   memcpy(buffer + HashSizeInBytes, data, len);
 
-  BLI_hash_md5_buffer(buffer, HashSizeInBytes + len, this);
+  const XXH128_hash_t hash = XXH3_128bits(buffer, len);
+  memcpy(this, &hash, sizeof(hash));
+  static_assert(sizeof(ComputeContextHash) == sizeof(hash));
 }
 
 std::ostream &operator<<(std::ostream &stream, const ComputeContextHash &hash)