util/disk_cache: try getenv(HOME) before getpwuid->pw_dir

getenv("HOME") is significantly faster than getpwuid_r(...)->pw_dir,
because the latter may require loading NSS libraries, reading
/etc/passwd, etc.

Furthermore, the Linux man pages for getpwuid_r recommend using
getenv("HOME") instead of getpwuid_r, because the user may wish to
change the value of HOME after logging in.

Signed-off-by: Manuel Stoeckl <code@mstoeckl.com>
Reviewed-by: Zoltán Böszörményi <zboszor@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13614>

src/util/disk_cache_os.c

@@ -879,6 +879,7 @@ disk_cache_write_item_to_disk(struct disk_cache_put_job *dc_job,
  *
  *   $MESA_SHADER_CACHE_DIR
  *   $XDG_CACHE_HOME/mesa_shader_cache
+ *   $HOME/.cache/mesa_shader_cache
  *   <pwd.pw_dir>/.cache/mesa_shader_cache
  */
 char *
@@ -924,6 +925,20 @@ disk_cache_generate_cache_dir(void *mem_ctx, const char *gpu_name,
       }
    }
 
+   if (!path) {
+      char *home = getenv("HOME");
+
+      if (home) {
+         path = concatenate_and_mkdir(mem_ctx, home, ".cache");
+         if (!path)
+            return NULL;
+
+         path = concatenate_and_mkdir(mem_ctx, path, cache_dir_name);
+         if (!path)
+            return NULL;
+      }
+   }
+
    if (!path) {
       char *buf;
       size_t buf_size;