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diff --git a/docs/DeveloperPolicy.rst b/docs/DeveloperPolicy.rst index 74a8979..508a04f 100644 --- a/docs/DeveloperPolicy.rst +++ b/docs/DeveloperPolicy.rst @@ -436,6 +436,29 @@ list, development list, or LLVM bug tracker component. If someone sends you a patch privately, encourage them to submit it to the appropriate list first. +IR Backwards Compatibility +-------------------------- + +When the IR format has to be changed, keep in mind that we try to maintain some +backwards compatibility. The rules are intended as a balance between convenience +for llvm users and not imposing a big burden on llvm developers: + +* The textual format is not backwards compatible. We don't change it too often, + but there are no specific promises. + +* The bitcode format produced by a X.Y release will be readable by all following + X.Z releases and the (X+1).0 release. + +* Newer releases can ignore features from older releases, but they cannot + miscompile them. For example, if nsw is ever replaced with something else, + dropping it would be a valid way to upgrade the IR. + +* Debug metadata is special in that it is currently dropped during upgrades. + +* Non-debug metadata is defined to be safe to drop, so a valid way to upgrade + it is to drop it. That is not very user friendly and a bit more effort is + expected, but no promises are made. + .. _copyright-license-patents: Copyright, License, and Patents |