Lisp interpreter micro-optimization

[Robert Pluim]

Hi,

I noticed we have an assq_no_quit, but no memq_no_quit, so came up
with the attached, which Iʼm convinced speeds up elisp by at least
.01% (Iʼm using Larsi-maths 😺), but Iʼm not convinced itʼs
worth pushing.

Robert
-- 

>From 6be3aedccd26fd20040be999a62874188f93469e Mon Sep 17 00:00:00 2001
From: Robert Pluim <rpluim@gmail.com>
Date: Tue, 26 Jul 2022 14:24:42 +0200
Subject: [PATCH] Add memq_no_quit
To: emacs-devel@gnu.org

We have an assq_no_quit, but no memq_no_quit. Add it and use it when
accessing Vinternal_interpreter_environment, which is always safe.

* src/fns.c (memq_no_quit): New function, no_quit version of 'memq'.
* src/lisp.h: Add 'memq_no_quit' prototype.

* src/eval.c (Fsetq): Use 'assq_no_quit'.
(FletX, Flet): Use 'memq_no_quit'.
(eval_sub): Use 'assq_no_quit'.
---
 src/eval.c |  8 ++++----
 src/fns.c  | 12 ++++++++++++
 src/lisp.h |  1 +
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/src/eval.c b/src/eval.c
index 141d2546f0..0477346d42 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -501,7 +501,7 @@ DEFUN ("setq", Fsetq, Ssetq, 0, UNEVALLED, 0,
       Lisp_Object lex_binding
        = ((!NILP (Vinternal_interpreter_environment) /* Mere optimization!  */
            && SYMBOLP (sym))
-          ? Fassq (sym, Vinternal_interpreter_environment)
+          ? assq_no_quit (sym, Vinternal_interpreter_environment)
           : Qnil);
       if (!NILP (lex_binding))
        XSETCDR (lex_binding, val); /* SYM is lexically bound.  */
@@ -947,7 +947,7 @@ DEFUN ("let*", FletX, SletX, 1, UNEVALLED, 0,
 
       if (!NILP (lexenv) && SYMBOLP (var)
          && !XSYMBOL (var)->u.s.declared_special
-         && NILP (Fmemq (var, Vinternal_interpreter_environment)))
+         && NILP (memq_no_quit (var, Vinternal_interpreter_environment)))
        /* Lexically bind VAR by adding it to the interpreter's binding
           alist.  */
        {
@@ -1022,7 +1022,7 @@ DEFUN ("let", Flet, Slet, 1, UNEVALLED, 0,
 
       if (!NILP (lexenv) && SYMBOLP (var)
          && !XSYMBOL (var)->u.s.declared_special
-         && NILP (Fmemq (var, Vinternal_interpreter_environment)))
+         && NILP (memq_no_quit (var, Vinternal_interpreter_environment)))
        /* Lexically bind VAR by adding it to the lexenv alist.  */
        lexenv = Fcons (Fcons (var, tem), lexenv);
       else
@@ -2354,7 +2354,7 @@ eval_sub (Lisp_Object form)
         already did that when let-binding the variable.  */
       Lisp_Object lex_binding
        = (!NILP (Vinternal_interpreter_environment) /* Mere optimization!  */
-          ? Fassq (form, Vinternal_interpreter_environment)
+          ? assq_no_quit (form, Vinternal_interpreter_environment)
           : Qnil);
       return !NILP (lex_binding) ? XCDR (lex_binding) : Fsymbol_value (form);
     }
diff --git a/src/fns.c b/src/fns.c
index 7e78bba3a0..fe3a01c2de 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -1785,6 +1785,18 @@ DEFUN ("memq", Fmemq, Smemq, 2, 2, 0,
   return Qnil;
 }
 
+/* Like Fmemq but never report an error and do not allow quits.
+   Use only on objects known to be non-circular lists.  */
+
+Lisp_Object
+memq_no_quit (Lisp_Object elt, Lisp_Object list)
+{
+  for (; ! NILP (list); list = XCDR (list))
+    if (EQ (XCAR (list), elt))
+      return list;
+  return Qnil;
+}
+
 DEFUN ("memql", Fmemql, Smemql, 2, 2, 0,
        doc: /* Return non-nil if ELT is an element of LIST.  Comparison done 
with `eql'.
 The value is actually the tail of LIST whose car is ELT.  */)
diff --git a/src/lisp.h b/src/lisp.h
index 8fcc9b6e75..e92540c258 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4033,6 +4033,7 @@ #define CONS_TO_INTEGER(cons, type, var)                  
        \
 extern Lisp_Object nconc2 (Lisp_Object, Lisp_Object);
 extern Lisp_Object assq_no_quit (Lisp_Object, Lisp_Object);
 extern Lisp_Object assoc_no_quit (Lisp_Object, Lisp_Object);
+extern Lisp_Object memq_no_quit (Lisp_Object, Lisp_Object);
 extern void clear_string_char_byte_cache (void);
 extern ptrdiff_t string_char_to_byte (Lisp_Object, ptrdiff_t);
 extern ptrdiff_t string_byte_to_char (Lisp_Object, ptrdiff_t);
-- 
2.37.1.116.g9dd64cb4d3