Recently we have again received several patches that are trying to add workarounds for ffmpegs use of DCE. This is not the first time this has happened and wont be the last until a decision is made about the use of DCE. So I think its time that we made a official decision on the use of DCE. This is of course something that should be properly agreed upon by developers going forward as different people have different opinions on the matter so to help assist this I will summaries all of the previously made arguments from both sides of the discussion.
For DCE: 1) Ends up with a horrible mess of ifdefs. 2) Disabled parts of code will not be checked for syntax. Against DCE: 3) DCE is not actually specified in the C specification. So compilers are actually being 100% compliant by not supporting it and should not be expected to change just for ffmpegs use case. 4) Breaks debug and lto builds on msvc. 5) Breaks debug and lto builds on icl. 6) Issues with lto with Clang and Gold. 7) Other unspecified issues with debug builds Rebuttals against above arguments: 8) There are already 3961 #ifs(not including header guards) in the code so there is already a lot of code that doesn't use DCE. (In response to #1 for DCE). 9) Avoiding #ifdefs is a personal opinion as to whether they are ugly or not (some prefer ifdefs as IDEs will correctly highlight disabled sections). Someones personal preference for what looks better should not be justification to break supported configurations/compilers. (In response to #1 for DCE). 10) There is --enable-random which is supposed to be used to find configurations that don't compile. (in response to #2 for DCE). 11) Just because something compiles does not mean that it actually works, relying on just syntax checking is dangerous as it gives false security as the code is not actually being tested. (in response to #2 for DCE) 12) There are numerous FATE tests that should find all the configuration errors. (in response to #2 for DCE) 12) MSVC is broken and we shouldn't support it so Microsoft are forced to fix it (in response to #4 against DCE) - This point is countermanded by #3 against DCE and reported issues with other compilers as well. Most of the above points were taken from peoples posts in the following mailing list thread: https://lists.ffmpeg.org/pipermail/ffmpeg-devel/2016-April/193437.html https://ffmpeg.org/pipermail/ffmpeg-devel/2016-May/194115.html Its my personal opinion that DCE should be removed from the code but this is something I am aware will require a developer consensus and perhaps even a vote. Stating something is broken is one thing so I will also put forward a solution in that if it is agreed upon to remove DCE usage then I will spend the time and effort to go through the existing code base and replace DCE with appropriate #ifs. Matt _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
