Subject: 28.0.50; [PATCH] substring and the byte compiler

From: Mark Oteiza <[email-masked]>
Date: Fri, 21 Feb 2020 01:22:06 -0500

Hi,

I don't really understand the byte compiler, but I noticed in
disassembly that substring, despite having an opcode, is getting
call'd:

10      constant  substring
11      stack-ref 3
12      constant  0
13      stack-ref 7
15      call      3

when really I'd expect to see something like

57      stack-ref 2
58      stack-ref 7
60      min       
61      stack-ref 7
63      substring 

The only relevant change I found is bug#33807.  Enlightenment welcome.
Naive patch below.

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index fce5e4aed6..ec340cd451 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -3506,6 +3506,7 @@ byte-defop-compiler
 					(0-1 . byte-compile-zero-or-one-arg)
 					(1-2 . byte-compile-one-or-two-args)
 					(2-3 . byte-compile-two-or-three-args)
+					(1-3 . byte-compile-one-to-three-args)
 					)))
 			   compile-handler
 			   (intern (concat "byte-compile-"
@@ -3690,6 +3691,13 @@ byte-compile-two-or-three-args
 	  ((= len 4) (byte-compile-three-args form))
 	  (t (byte-compile-subr-wrong-args form "2-3")))))
 
+(defun byte-compile-one-to-three-args (form)
+  (let ((len (length form)))
+    (cond ((= len 2) (byte-compile-one-arg form))
+          ((= len 3) (byte-compile-two-args form))
+          ((= len 4) (byte-compile-three-args form))
+	  (t (byte-compile-subr-wrong-args form "1-3")))))
+
 (defun byte-compile-noop (_form)
   (byte-compile-constant nil))
 
diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index fe0930c684..d3c84335ec 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -1511,11 +1511,11 @@ byte-compile-side-effect-and-error-free-ops
 (defconst byte-compile-side-effect-free-ops
   (nconc
    '(byte-varref byte-nth byte-memq byte-car byte-cdr byte-length byte-aref
-     byte-symbol-value byte-get byte-concat2 byte-concat3 byte-sub1 byte-add1
-     byte-eqlsign byte-gtr byte-lss byte-leq byte-geq byte-diff byte-negate
-     byte-plus byte-max byte-min byte-mult byte-char-after byte-char-syntax
-     byte-buffer-substring byte-string= byte-string< byte-nthcdr byte-elt
-     byte-member byte-assq byte-quo byte-rem)
+     byte-symbol-value byte-get byte-substring byte-concat2 byte-concat3
+     byte-sub1 byte-add1 byte-eqlsign byte-gtr byte-lss byte-leq byte-geq
+     byte-diff byte-negate byte-plus byte-max byte-min byte-mult byte-char-after
+     byte-char-syntax byte-buffer-substring byte-string= byte-string<
+     byte-nthcdr byte-elt byte-member byte-assq byte-quo byte-rem)
    byte-compile-side-effect-and-error-free-ops))
 
 ;; This crock is because of the way DEFVAR_BOOL variables work.