master 1ece474c69c 1/2: Slight funcall_subr optimisation

[Mattias Engdegård]

branch: master
commit 1ece474c69cfcf6f8ef14d54e469eb387a7a6983
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    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).
---
 src/eval.c | 18 ++++++++----------
 1 file 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);
     }