I just had a look at the source code of the GNU C compiler
snapshot 20091121, version 4.4, looking for the "inefficient use of strlen in
a for loop" pattern.
For file gcc/gengtype.c
$ grep "for.*;.*strlen.*;" gcc/gengtype.c
for (aindex = 0; aindex < strlen (rtx_format[i]); aindex++)
for (nmindex = 0; nmindex < strlen (ftag); nmindex++)
I checked the source code and it seems to me that the strlens may
be moved outside the for loop to speed up the code
from quadratic to linear and simplify the code.
I tried out my idea and the compiler seemed to bootstrap ok.
Here is a patch
--- gcc/gengtype.c.sav 2008-11-28 11:47:25.000000000 +0000
+++ gcc/gengtype.c 2008-11-28 11:49:57.000000000 +0000
@@ -1062,8 +1062,10 @@
const char *sname;
type_p substruct;
char *ftag;
+ const size_t dcb_len1 = strlen (rtx_format[i]);
+ size_t dcb_len2;
- for (aindex = 0; aindex < strlen (rtx_format[i]); aindex++)
+ for (aindex = 0; aindex < dcb_len1; aindex++)
{
type_p t;
const char *subname;
@@ -1192,7 +1194,8 @@
substruct = new_structure (sname, 0, &lexer_line, subfields, NULL);
ftag = xstrdup (rtx_name[i]);
- for (nmindex = 0; nmindex < strlen (ftag); nmindex++)
+ dcb_len2 = strlen( ftag);
+ for (nmindex = 0; nmindex < dcb_len2; nmindex++)
ftag[nmindex] = TOUPPER (ftag[nmindex]);
flds = create_field (flds, substruct, "");
--
Summary: inefficient use of strlen in for loop
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: bootstrap
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: dcb314 at hotmail dot com
GCC host triplet: suse_linux-x86_64
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38302
