From: Mattias Engdegård <mattiase@acm.org>
Date: Tue, 21 Nov 2023 10:23:57 +0000 (+0100)
Subject: Slight funcall_subr optimisation
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=1ece474c69cfcf6f8ef14d54e469eb387a7a6983;p=emacs.git

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).
---

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);
     }