1 files changed, 12 insertions, 0 deletions
diff --git a/job.c b/job.c
index f00b6af..9d11ffc 100644
--- a/job.c
+++ b/job.c
@@ -785,6 +785,18 @@ start_job_command (child)
   message (0, (just_print_flag || (!(flags & COMMANDS_SILENT) && !silent_flag))
 	   ? "%s" : (char *) 0, p);
 
+  /* Optimize an empty command.  People use this for timestamp rules,
+     and forking a useless shell all the time leads to inefficiency. */
+
+  if ((argv[0]      && !strcmp(argv[0], "/bin/sh"))
+      && (argv[1]   && !strcmp(argv[1], "-c"))
+      && (argv[2]   && !strcmp(argv[2], ":"))
+      && argv[3] == NULL)
+    {
+      set_command_state (child->file, cs_running);
+      goto next_command;
+    }
+
   /* Tell update_goal_chain that a command has been started on behalf of
      this target.  It is important that this happens here and not in
      reap_children (where we used to do it), because reap_children might be