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Don't compute the file size if we don't need to.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127426 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola 2011-03-10 20:54:07 +00:00
parent fa0e6facc7
commit 9d2234d6a0
1 changed files with 29 additions and 14 deletions
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43
lib/Support/MemoryBuffer.cpp
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@ -216,7 +216,8 @@ error_code MemoryBuffer::getFile(const char *Filename,
return ret;
}
static bool shouldUseMmap(size_t FileSize,
static bool shouldUseMmap(int FD,
size_t FileSize,
size_t MapSize,
off_t Offset,
bool RequiresNullTerminator,
@ -229,6 +230,20 @@ static bool shouldUseMmap(size_t FileSize,
if (!RequiresNullTerminator)
return true;
// If we don't know the file size, use fstat to find out. fstat on an open
// file descriptor is cheaper than stat on a random path.
// FIXME: this chunk of code is duplicated, but it avoids a fstat when
// RequiresNullTerminator = false and MapSize != -1.
if (FileSize == size_t(-1)) {
struct stat FileInfo;
// TODO: This should use fstat64 when available.
if (fstat(FD, &FileInfo) == -1) {
return error_code(errno, posix_category());
}
FileSize = FileInfo.st_size;
}
// If we need a null terminator and the end of the map is inside the file,
// we cannot use mmap.
size_t End = Offset + MapSize;
@ -251,22 +266,22 @@ error_code MemoryBuffer::getOpenFile(int FD, const char *Filename,
bool RequiresNullTerminator) {
static int PageSize = sys::Process::GetPageSize();
// If we don't know the file size, use fstat to find out. fstat on an open
// file descriptor is cheaper than stat on a random path.
if (FileSize == size_t(-1)) {
struct stat FileInfo;
// TODO: This should use fstat64 when available.
if (fstat(FD, &FileInfo) == -1) {
return error_code(errno, posix_category());
// Default is to map the full file.
if (MapSize == size_t(-1)) {
// If we don't know the file size, use fstat to find out. fstat on an open
// file descriptor is cheaper than stat on a random path.
if (FileSize == size_t(-1)) {
struct stat FileInfo;
// TODO: This should use fstat64 when available.
if (fstat(FD, &FileInfo) == -1) {
return error_code(errno, posix_category());
}
FileSize = FileInfo.st_size;
}
FileSize = FileInfo.st_size;
MapSize = FileSize;
}
// Default is to map the full file.
if (MapSize == size_t(-1))
MapSize = FileSize;
if (shouldUseMmap(FileSize, MapSize, Offset, RequiresNullTerminator,
if (shouldUseMmap(FD, FileSize, MapSize, Offset, RequiresNullTerminator,
PageSize)) {
off_t RealMapOffset = Offset & ~(PageSize - 1);
off_t Delta = Offset - RealMapOffset;