Slight funcall_subr optimisation

* src/eval.c (funcall_subr): Help the compiler by reducing aliasing
problems, and compensate for a missed-optimisation bug in LLVM where
switches sometimes forget to use variable range information (reported
in https://github.com/llvm/llvm-project/issues/76085).

1 files changed, 8 insertions, 10 deletions

diff --git a/src/eval.c b/src/eval.c
index 5c9052cb9ab..b3d3fc3132b 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -3033,21 +3033,21 @@ funcall_subr (struct Lisp_Subr *subr, ptrdiff_t numargs, Lisp_Object *args)
   if (numargs >= subr->min_args)
     {
       /* Conforming call to finite-arity subr.  */
-      if (numargs <= subr->max_args
-          && subr->max_args <= 8)
+      ptrdiff_t maxargs = subr->max_args;
+      if (numargs <= maxargs && maxargs <= 8)
         {
           Lisp_Object argbuf[8];
           Lisp_Object *a;
-          if (numargs < subr->max_args)
+          if (numargs < maxargs)
             {
-              eassume (subr->max_args <= ARRAYELTS (argbuf));
+              eassume (maxargs <= ARRAYELTS (argbuf));
               a = argbuf;
               memcpy (a, args, numargs * word_size);
-              memclear (a + numargs, (subr->max_args - numargs) * word_size);
+              memclear (a + numargs, (maxargs - numargs) * word_size);
             }
           else
             a = args;
-          switch (subr->max_args)
+          switch (maxargs)
             {
             case 0:
               return subr->function.a0 ();
@@ -3069,14 +3069,12 @@ funcall_subr (struct Lisp_Subr *subr, ptrdiff_t numargs, Lisp_Object *args)
             case 8:
               return subr->function.a8 (a[0], a[1], a[2], a[3], a[4], a[5],
                                         a[6], a[7]);
-            default:
-              emacs_abort ();   /* Can't happen. */
             }
+          eassume (false);      /* In case the compiler is too stupid.  */
         }
 
       /* Call to n-adic subr.  */
-      if (subr->max_args == MANY
-          || subr->max_args > 8)
+      if (maxargs == MANY || maxargs > 8)
         return subr->function.aMANY (numargs, args);
     }