master a3aeee88aa 1/2: Minor `concat` tweaks

[Mattias Engdegård]

branch: master
commit a3aeee88aaf843de49e4815e4b2d61743e423441
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Minor `concat` tweaks
    
    * src/fns.c (concat): Do things in the right order for speed.
    (concat_strings): Initialise variable.
---
 src/fns.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/src/fns.c b/src/fns.c
index 87237f3b5e..16f1ebe439 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -790,9 +790,8 @@ concat_strings (ptrdiff_t nargs, Lisp_Object *args)
 
       if (STRINGP (arg))
        {
-         ptrdiff_t arg_len_byte;
+         ptrdiff_t arg_len_byte = SBYTES (arg);
          len = SCHARS (arg);
-         arg_len_byte = SBYTES (arg);
          if (STRING_MULTIBYTE (arg))
            dest_multibyte = true;
          else
@@ -986,15 +985,16 @@ concat (ptrdiff_t nargs, Lisp_Object *args, Lisp_Object 
last_tail,
        memory_full (SIZE_MAX);
     }
 
+  /* When the target is a list, return the tail directly if all other
+     arguments are empty.  */
+  if (!vector_target && result_len == 0)
+    return last_tail;
+
   /* Create the output object.  */
   Lisp_Object result = vector_target
     ? make_nil_vector (result_len)
     : Fmake_list (make_fixnum (result_len), Qnil);
 
-  /* In `append', if all but last arg are nil, return last arg.  */
-  if (!vector_target && NILP (result))
-    return last_tail;
-
   /* Copy the contents of the args into the result.  */
   Lisp_Object tail = Qnil;
   ptrdiff_t toindex = 0;
@@ -1022,14 +1022,12 @@ concat (ptrdiff_t nargs, Lisp_Object *args, Lisp_Object 
last_tail,
          /* Fetch next element of `arg' arg into `elt', or break if
             `arg' is exhausted. */
          Lisp_Object elt;
-         if (NILP (arg))
-           break;
          if (CONSP (arg))
            {
              elt = XCAR (arg);
              arg = XCDR (arg);
            }
-         else if (argindex >= arglen)
+         else if (NILP (arg) || argindex >= arglen)
            break;
          else if (STRINGP (arg))
            {