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Bill Wendling 353fbd3516 Performance improvement. Using fwrite and fread was very very slow. The resulting code was multiple times slower than GCC's implementation of gcov. Replace the fwrite/fread system with an mmap() version. If the `.gcda' file doesn't exist, we (re)allocate a buffer that we write into. That gets written to the `.gcda' file in one chunk. If the `.gcda' file already exists, we simply mmap() the file, modify the mapped data, and use msync() to write the contents out to disk. It's much easier than implementing our own buffering scheme, and we don't have to use fwrite's and fread's buffering. For those who are numbers-oriented, here are some timings: GCC Verison ----------- `.gcda' files don't exist: 23s `.gcda' files do exist: 14s LLVM Version (before this change) --------------------------------- `.gcda' files don't exist: 28s `.gcda' files do exist: 28s LLVM Version (with this change) ------------------------------- `.gcda' files don't exist: 18s `.gcda' files do exist: 4s It's a win-win-win-win-lose-win-win scenario! <rdar://problem/13466086> llvm-svn: 182563	2013-05-23 07:18:59 +00:00
..
usr/include	Performance improvement.	2013-05-23 07:18:59 +00:00
README.txt	SDKs: Sketch an initial stub SDK for Linux, I believe this suffices for building	2011-12-08 02:39:23 +00:00

Bill Wendling 353fbd3516 Performance improvement.

Using fwrite and fread was very *very* slow. The resulting code was multiple
times slower than GCC's implementation of gcov. Replace the fwrite/fread system
with an mmap() version.

If the `.gcda' file doesn't exist, we (re)allocate a buffer that we write
into. That gets written to the `.gcda' file in one chunk. If the `.gcda' file
already exists, we simply mmap() the file, modify the mapped data, and use
msync() to write the contents out to disk. It's much easier than implementing
our own buffering scheme, and we don't have to use fwrite's and fread's
buffering.

For those who are numbers-oriented, here are some timings:

GCC Verison
-----------

`.gcda' files don't exist:  23s
`.gcda' files do exist:     14s

LLVM Version (before this change)
---------------------------------

`.gcda' files don't exist:  28s
`.gcda' files do exist:     28s

LLVM Version (with this change)
-------------------------------

`.gcda' files don't exist:  18s
`.gcda' files do exist:      4s

It's a win-win-win-win-lose-win-win scenario!

<rdar://problem/13466086>

llvm-svn: 182563

2013-05-23 07:18:59 +00:00

usr/include

Performance improvement.

2013-05-23 07:18:59 +00:00

README.txt

SDKs: Sketch an initial stub SDK for Linux, I believe this suffices for building

2011-12-08 02:39:23 +00:00

README.txt

This is a stub SDK for Linux. Currently, this has only been tested on i386 and
x86_64 using the Clang compiler.