svn commit: r187369 - head/lib/libc/stdio

[David Schultz]

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;