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Changed README to README.md. Updated the README with additional information.
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gavin.smith@coralbay.tv
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Make FMV patches
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The Clear Linux project is currently focusing on applying FMV technology to
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packages where it is detected that AVX instructions can yield an improvement.
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To solve some of the issues involved with supporting FMV in a full Linux
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distribution, the project provides a patch generator based on
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vectorization-candidate detection (using the -fopt-info-vec flag). This tool
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can provide all the FMV patches that a Linux distribution might use
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----------------------
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Command Line Arguments
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----------------------
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Example: perl make-fmv-patch.pl <buildlog> <sourcecode>
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buildlog: Build of the compilation of source code in gcc using the
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``-fopt-info-vec`` flag
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sourcecode: Absolute path to the source file from where patches will be
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generated
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------------
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Requirements
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------------
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- Exuberant ctags:
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In order to use `make-fvm-patch.pl` your system will need Exuberant Ctags
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(https://sourceforge.net/projects/ctags/), this is due to the `--c-kinds`
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ctags' flag usage.
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------------
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Test examples
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------------
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```
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cd tests
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make
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cd ..
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perl make-fmv-patch.pl tests/max-build.log tests/
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perl make-fmv-patch.pl tests/loop-build.log tests/
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This will generate:
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./tests/max-test.cpp.patch
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./tests/loop-test.c.patch
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```
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# Make FMV patch generator
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The Clear Linux project is currently focusing on applying **function multi-version (FMV)** technology to packages where it is detected that AVX instructions can yield a performance improvement. To solve some of the issues involved with supporting FMV in a full Linux distribution, the project provides a patch generator based on vectorization-candidate detection (using the gcc `-fopt-info-vec` compiler flag). This tool can provide all the FMV patches that a Linux distribution might use.
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Although this patch tool was originally designed to be used for Clear Linux OS, the patch generator can be applied to any project built with gcc.
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## Example
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The following sample code will be used:
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```c
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/time.h>
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#define MAX 1000000
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int a[256], b[256], c[256];
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void foo()
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{
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int i,x;
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for (x=0; x<MAX; x++)
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{
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for (i=0; i<256; i++)
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{
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a[i] = b[i] + c[i];
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}
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}
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}
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int main()
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{
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foo();
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return 0;
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}
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```
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### 1. Compile the code:
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`gcc -O2 -ftree-vectorize -fopt-info-vec example.c -o example &> log.txt
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`
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Breaking down the command:
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* The `-ftree-vectorize` flag enables vectorization. *Note*: it is enabled by default at `-O3`
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* The `-fopt-info-vec` generates a report to stdout providing details of code that the compiler was able to vectorize.
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* The `&> log.txt` pipes the output to a file of the same name.
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Upon examing the log.txt file (using `cat log.txt`), it can be seen that gcc was able to vectorize parts of the code:
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```
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example.c:13:13: note: loop vectorized
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example.c:13:13: note: loop vectorized
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```
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### 2. Generate the FMV patch
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The patch tool takes the format
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`perl make-fmv-patch.pl <buildlog> <sourcecode>`
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After checking out the tool from the repository, run the patch tool using `log.txt` as input:
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```perl make-fmv-patch.pl log.txt .```
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Upon completion, the patch tool will output log confirming that example.c has been patched:
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```patching ./example.c @ lines (8)```
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The command generates the following example.c.patch patch:
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```
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--- ./example.c 2019-01-13 00:04:47.646072680 +0000
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+++ ./example.c~ 2019-01-13 00:04:57.586072680 +0000
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@@ -5,6 +5,7 @@
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int a[256], b[256], c[256];
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+__attribute__((target_clones("avx2","arch=atom","default")))
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void foo()
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{
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int i,x;
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```
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### Apply the patch
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Using the example.c.patch file, apply the patch to example.c:
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```patch -p1 < example.c.patch```
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The example.c file should have been patched, and look something like:
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```c
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/time.h>
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#define MAX 1000000
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int a[256], b[256], c[256];
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__attribute__((target_clones("avx2","arch=atom","default")))
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void foo()
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{
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int i,x;
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for (x=0; x<MAX; x++)
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{
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for (i=0; i<256; i++)
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{
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a[i] = b[i] + c[i];
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}
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}
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}
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int main()
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{
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foo();
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return 0;
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}
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```
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### Recompile the code
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Compile the code again (with FMV syntax having been applied to the code):
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```gcc -O2 -ftree-vectorize -fopt-info-vec example.c -o example```
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The console output should contain:
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```
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example.c:14:13: note: loop vectorized
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example.c:14:13: note: loop vectorized
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example.c:14:13: note: loop vectorized
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```
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Voila!
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## Requirements
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- GCC v6 compiler or newer
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- Perl
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- Exuberant ctags:
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In order to use `make-fvm-patch.pl` your system will need Exuberant Ctags
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(https://sourceforge.net/projects/ctags/), this is due to the `--c-kinds`
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ctags' flag usage.
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## Test examples
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The repostory makes available a tests directory. Users can use the tests directory to conduct their own tests and/or share issues with sample code (for easy reproducability).
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```bash
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cd tests
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make
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cd ..
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```
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Once built, follow the steps outlined in the example above:
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```bash
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perl make-fmv-patch.pl tests/max-build.log tests/
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perl make-fmv-patch.pl tests/loop-build.log tests/
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```
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then...
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* Apply the patches
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* Recompile the code
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* Run
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## Further Reading
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* Clear Linux: [Use the function multi-version patch generator](https://clearlinux.org/documentation/clear-linux/tutorials/fmv)
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