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. |