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Changes between Version 41 and Version 42 of CompilationGuide

v41	v42
33	33	There are numerous avenues to extract maximum performance out of FFmpeg when it is built from source. The following list describes some of them:
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35		* If using {{{GCC}}}, consider adding {{{-ftree-vectorize}}} to {{{--extra-cflags}}}. Most recent versions of {{{GCC}}} do not miscompile FFmpeg with the auto-vectorizer enabled, and can easily reap a general 1-2% increase in performance from a FATE run ({{{make fate-rsync; make fate}}}), with gains varying across the codebase and compiler version. However, the project does not currently maintain a list of compiler versions under which the vectorizer works correctly, since even recent releases like {{{4.8.0}}} had problems. Therefore, {{{configure}}} by default disables the auto-vectorizer on {{{GCC}}}, and it must be enabled by the user explicitly if desired, such as via the method outlined above. It is highly advised to test at least a FATE run to ensure that things work correctly when the auto-vectorizer is turned on.
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37	35	* If using {{{GCC/Clang}}}, consider adding {{{-march=native}}} to {{{--extra-cflags}}} to make slightly better use of your hardware. Alternatively, for a more general solution, examine the {{{--arch}}} and {{{--cpu}}} options. Gains are variable, and usually quite small. However, this is usually even more safe than the above, and is thus listed here.
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