GNU bug report logs - #24378
[PATCH 0/6] Small fixes and improvements

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From: Michal Nazarewicz <mina86 <at> mina86.com>
To: 24378 <at> debbugs.gnu.org
Subject: bug#24378: [PATCH 4/6] Remove dead loop iterations in regex.c
Date: Tue,  6 Sep 2016 15:31:32 +0200

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

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