Add configure checking for pread(2) and use it to save a syscall when reading files.

llvm-svn: 145061
This commit is contained in:
Benjamin Kramer 2011-11-22 12:31:53 +00:00
parent 63f2a37e6e
commit 7120c3ef01
6 changed files with 18 additions and 2 deletions

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@ -1293,7 +1293,7 @@ AC_CHECK_FUNCS([backtrace ceilf floorf roundf rintf nearbyintf getcwd ])
AC_CHECK_FUNCS([powf fmodf strtof round ])
AC_CHECK_FUNCS([getpagesize getrusage getrlimit setrlimit gettimeofday ])
AC_CHECK_FUNCS([isatty mkdtemp mkstemp ])
AC_CHECK_FUNCS([mktemp posix_spawn realpath sbrk setrlimit strdup ])
AC_CHECK_FUNCS([mktemp posix_spawn pread realpath sbrk setrlimit strdup ])
AC_CHECK_FUNCS([strerror strerror_r setenv ])
AC_CHECK_FUNCS([strtoll strtoq sysconf malloc_zone_statistics ])
AC_CHECK_FUNCS([setjmp longjmp sigsetjmp siglongjmp writev])

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@ -126,6 +126,8 @@ check_symbol_exists(readdir "sys/types.h;dirent.h" HAVE_READDIR)
check_symbol_exists(getcwd unistd.h HAVE_GETCWD)
check_symbol_exists(gettimeofday sys/time.h HAVE_GETTIMEOFDAY)
check_symbol_exists(getrlimit "sys/types.h;sys/time.h;sys/resource.h" HAVE_GETRLIMIT)
check_symbol_exists(posix_spawn spawn.h HAVE_POSIX_SPAWN)
check_symbol_exists(pread unistd.h HAVE_PREAD)
check_symbol_exists(rindex strings.h HAVE_RINDEX)
check_symbol_exists(strchr string.h HAVE_STRCHR)
check_symbol_exists(strcmp string.h HAVE_STRCMP)

3
configure vendored
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@ -17151,7 +17151,8 @@ done
for ac_func in mktemp posix_spawn realpath sbrk setrlimit strdup
for ac_func in mktemp posix_spawn pread realpath sbrk setrlimit strdup
do
as_ac_var=`echo "ac_cv_func_$ac_func" | $as_tr_sh`
{ echo "$as_me:$LINENO: checking for $ac_func" >&5

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@ -297,6 +297,9 @@
/* Define to 1 if you have the `powf' function. */
#cmakedefine HAVE_POWF ${HAVE_POWF}
/* Define to 1 if you have the `pread' function. */
#cmakedefine HAVE_PREAD ${HAVE_PREAD}
/* Define if libtool can extract symbol lists from object files. */
#undef HAVE_PRELOADED_SYMBOLS

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@ -295,6 +295,9 @@
/* Define to 1 if you have the `powf' function. */
#undef HAVE_POWF
/* Define to 1 if you have the `pread' function. */
#undef HAVE_PREAD
/* Define if libtool can extract symbol lists from object files. */
#undef HAVE_PRELOADED_SYMBOLS

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@ -14,6 +14,7 @@
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Config/config.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/Errno.h"
#include "llvm/Support/Path.h"
@ -320,11 +321,17 @@ error_code MemoryBuffer::getOpenFile(int FD, const char *Filename,
char *BufPtr = const_cast<char*>(SB->getBufferStart());
size_t BytesLeft = MapSize;
#ifndef HAVE_PREAD
if (lseek(FD, Offset, SEEK_SET) == -1)
return error_code(errno, posix_category());
#endif
while (BytesLeft) {
#ifdef HAVE_PREAD
ssize_t NumRead = ::pread(FD, BufPtr, BytesLeft, MapSize-BytesLeft+Offset);
#else
ssize_t NumRead = ::read(FD, BufPtr, BytesLeft);
#endif
if (NumRead == -1) {
if (errno == EINTR)
continue;