Author: das
Date: Sat Jan 17 18:57:12 2009
New Revision: 187369
URL: http://svn.freebsd.org/changeset/base/187369
Log:
When f[w]printf() is called on an unbuffered file like stdout, it
sets up a fake buffered FILE and then effectively calls itself
recursively. Unfortunately, gcc doesn't know how to do tail call
elimination in this case, and actually makes things worse by
inlining __sbprintf(). This means that f[w]printf() to stderr was
allocating about 5k of stack on 64-bit platforms, much of which was
never used.
I've reorganized things to eliminate the waste. In addition to saving
some stack space, this improves performance in my tests by anywhere
from 5% to 17% (depending on the test) when -fstack-protector is
enabled. I found no statistically significant performance difference
when stack protection is turned off. (The tests redirected stderr to
/dev/null.)
Modified:
head/lib/libc/stdio/vfprintf.c
head/lib/libc/stdio/vfwprintf.c
Modified: head/lib/libc/stdio/vfprintf.c
==============================================================================
--- head/lib/libc/stdio/vfprintf.c Sat Jan 17 17:40:44 2009
(r187368)
+++ head/lib/libc/stdio/vfprintf.c Sat Jan 17 18:57:12 2009
(r187369)
@@ -65,7 +65,8 @@ __FBSDID("$FreeBSD$");
#include "printflocal.h"
static int __sprint(FILE *, struct __suio *);
-static int __sbprintf(FILE *, const char *, va_list) __printflike(2, 0);
+static int __sbprintf(FILE *, const char *, va_list) __printflike(2, 0)
+ __noinline;
static char *__wcsconv(wchar_t *, int);
#define CHAR char
@@ -102,6 +103,10 @@ __sbprintf(FILE *fp, const char *fmt, va
FILE fake;
unsigned char buf[BUFSIZ];
+ /* XXX This is probably not needed. */
+ if (prepwrite(fp) != 0)
+ return (EOF);
+
/* copy the important variables */
fake._flags = fp->_flags & ~__SNBF;
fake._file = fp->_file;
@@ -193,7 +198,12 @@ vfprintf(FILE * __restrict fp, const cha
int ret;
FLOCKFILE(fp);
- ret = __vfprintf(fp, fmt0, ap);
+ /* optimise fprintf(stderr) (and other unbuffered Unix files) */
+ if ((fp->_flags & (__SNBF|__SWR|__SRW)) == (__SNBF|__SWR) &&
+ fp->_file >= 0)
+ ret = __sbprintf(fp, fmt0, ap);
+ else
+ ret = __vfprintf(fp, fmt0, ap);
FUNLOCKFILE(fp);
return (ret);
}
@@ -367,11 +377,6 @@ __vfprintf(FILE *fp, const char *fmt0, v
if (prepwrite(fp) != 0)
return (EOF);
- /* optimise fprintf(stderr) (and other unbuffered Unix files) */
- if ((fp->_flags & (__SNBF|__SWR|__SRW)) == (__SNBF|__SWR) &&
- fp->_file >= 0)
- return (__sbprintf(fp, fmt0, ap));
-
thousands_sep = '\0';
grouping = NULL;
convbuf = NULL;
Modified: head/lib/libc/stdio/vfwprintf.c
==============================================================================
--- head/lib/libc/stdio/vfwprintf.c Sat Jan 17 17:40:44 2009
(r187368)
+++ head/lib/libc/stdio/vfwprintf.c Sat Jan 17 18:57:12 2009
(r187369)
@@ -67,7 +67,7 @@ __FBSDID("$FreeBSD$");
#include "printflocal.h"
static int __sprint(FILE *, struct __suio *);
-static int __sbprintf(FILE *, const wchar_t *, va_list);
+static int __sbprintf(FILE *, const wchar_t *, va_list) __noinline;
static wint_t __xfputwc(wchar_t, FILE *);
static wchar_t *__mbsconv(char *, int);
@@ -114,6 +114,10 @@ __sbprintf(FILE *fp, const wchar_t *fmt,
FILE fake;
unsigned char buf[BUFSIZ];
+ /* XXX This is probably not needed. */
+ if (prepwrite(fp) != 0)
+ return (EOF);
+
/* copy the important variables */
fake._flags = fp->_flags & ~__SNBF;
fake._file = fp->_file;
@@ -250,7 +254,12 @@ vfwprintf(FILE * __restrict fp, const wc
int ret;
FLOCKFILE(fp);
- ret = __vfwprintf(fp, fmt0, ap);
+ /* optimise fprintf(stderr) (and other unbuffered Unix files) */
+ if ((fp->_flags & (__SNBF|__SWR|__SRW)) == (__SNBF|__SWR) &&
+ fp->_file >= 0)
+ ret = __sbprintf(fp, fmt0, ap);
+ else
+ ret = __vfwprintf(fp, fmt0, ap);
FUNLOCKFILE(fp);
return (ret);
}
@@ -419,11 +428,6 @@ __vfwprintf(FILE *fp, const wchar_t *fmt
if (prepwrite(fp) != 0)
return (EOF);
- /* optimise fprintf(stderr) (and other unbuffered Unix files) */
- if ((fp->_flags & (__SNBF|__SWR|__SRW)) == (__SNBF|__SWR) &&
- fp->_file >= 0)
- return (__sbprintf(fp, fmt0, ap));
-
thousands_sep = '\0';
grouping = NULL;
convbuf = NULL;
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