nicolas/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

The final result of all this refactoring: instead of doing stat immediately

Browse Source 
followed by an open for every source file we open, probe the file system with
'open' and then do an fstat when it succeeds.  open+fstat is faster than
stat+open because the kernel only has to perform the string->inode mapping
once.  Presumably it gets faster the deeper in your filesystem a lookup
happens.

For -Eonly on cocoa.h, this reduces system time from 0.042s to 0.039s on
my machine, a 7.7% speedup.

llvm-svn: 120066
This commit is contained in:
Chris Lattner
2010-11-23 22:32:37 +00:00
parent 6bf4e6d8b2
commit 5ea7d07d2a
3 changed files with 55 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

41
clang/lib/Basic/FileSystemStatCache.cpp
View File

@@ -13,6 +13,7 @@
#include "clang/Basic/FileSystemStatCache.h"
#include "llvm/System/Path.h"
#include <fcntl.h>
// FIXME: This is terrible, we need this for ::close.
#if !defined(_MSC_VER) && !defined(__MINGW32__)
@@ -39,18 +40,52 @@ using namespace clang;
bool FileSystemStatCache::get(const char *Path, struct stat &StatBuf,
int *FileDescriptor, FileSystemStatCache *Cache) {
LookupResult R;
bool isForDir = FileDescriptor == 0;
// If we have a cache, use it to resolve the stat query.
if (Cache)
R = Cache->getStat(Path, StatBuf, FileDescriptor);
else
else if (isForDir) {
// If this is a directory and we have no cache, just go to the file system.
R = ::stat(Path, &StatBuf) != 0 ? CacheMissing : CacheExists;
} else {
// Otherwise, we have to go to the filesystem. We can always just use
// 'stat' here, but (for files) the client is asking whether the file exists
// because it wants to turn around and *open* it. It is more efficient to
// do "open+fstat" on success than it is to do "stat+open".
//
// Because of this, check to see if the file exists with 'open'. If the
// open succeeds, use fstat to get the stat info.
int OpenFlags = O_RDONLY;
#ifdef O_BINARY
OpenFlags |= O_BINARY; // Open input file in binary mode on win32.
#endif
*FileDescriptor = ::open(Path, OpenFlags);
if (*FileDescriptor == -1) {
// If the open fails, our "stat" fails.
R = CacheMissing;
} else {
// Otherwise, the open succeeded. Do an fstat to get the information
// about the file. We'll end up returning the open file descriptor to the
// client to do what they please with it.
if (::fstat(*FileDescriptor, &StatBuf) == 0)
R = CacheExists;
else {
// fstat rarely fails. If it does, claim the initial open didn't
// succeed.
R = CacheMissing;
::close(*FileDescriptor);
*FileDescriptor = -1;
}
}
}
// If the path doesn't exist, return failure.
if (R == CacheMissing) return true;
// If the path exists, make sure that its "directoryness" matches the clients
// demands.
bool isForDir = FileDescriptor == 0;
if (S_ISDIR(StatBuf.st_mode) != isForDir) {
// If not, close the file if opened.
if (FileDescriptor && *FileDescriptor != -1) {