bug#24378: [PATCH 4/6] Remove dead loop iterations in regex.c

[Michal Nazarewicz]

RE_CHAR_TO_MULTIBYTE(c) yields c for ASCII characters and a byte8
character for c ≥ 0x80.  Furthermore, CHAR_BYTE8_P(c) is true only
for byte8 characters.  This means that

        c = RE_CHAR_TO_MULTIBYTE (ch);
        if (! CHAR_BYTE8_P (c) && re_iswctype (c, cc))

is equivalent to:

        c = c;
        if (! false && re_iswctype (c, cc))

for 0 ⪬ c < 0x80, and

        c = BYTE8_TO_CHAR (c);
        if (! true && re_iswctype (c, cc))

for 0x80 ⪬ c < 0x100.  In other words, the loop never executes for
c ≥ 0x80 and RE_CHAR_TO_MULTIBYTE call is unnecessary for c < 0x80.

* src/regex.c (regex_compile): Simplyfy a for loop by eliminating
dead iterations and unnecessary macro calls.
---
 src/regex.c | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/src/regex.c b/src/regex.c
index 5f51b43..41c1d3f 100644
--- a/src/regex.c
+++ b/src/regex.c
@@ -2888,22 +2888,18 @@ regex_compile (const_re_char *pattern, size_t size,
                       done until now.  */
                    SETUP_BUFFER_SYNTAX_TABLE ();
 
-                   for (ch = 0; ch < 256; ++ch)
-                     {
-                       c = RE_CHAR_TO_MULTIBYTE (ch);
-                       if (! CHAR_BYTE8_P (c)
-                           && re_iswctype (c, cc))
-                         {
-                           SET_LIST_BIT (ch);
-                           c1 = TRANSLATE (c);
-                           if (c1 == c)
-                             continue;
-                           if (ASCII_CHAR_P (c1))
-                             SET_LIST_BIT (c1);
-                           else if ((c1 = RE_CHAR_TO_UNIBYTE (c1)) >= 0)
-                             SET_LIST_BIT (c1);
-                         }
-                     }
+                   for (c = 0; c < 0x80; ++c)
+                     if (re_iswctype (c, cc))
+                       {
+                         SET_LIST_BIT (c);
+                         c1 = TRANSLATE (c);
+                         if (c1 == c)
+                           continue;
+                         if (ASCII_CHAR_P (c1))
+                           SET_LIST_BIT (c1);
+                         else if ((c1 = RE_CHAR_TO_UNIBYTE (c1)) >= 0)
+                           SET_LIST_BIT (c1);
+                       }
                    SET_RANGE_TABLE_WORK_AREA_BIT
                      (range_table_work, re_wctype_to_bit (cc));
 #endif /* emacs */
-- 
2.8.0.rc3.226.g39d4020