[llvm-commits] PATCH: Add Version.h and macros

[Daniel Dunbar]

The attached patch adds llvm/Version.h, which provides the following
defines:
LLVM_VERSION_MAJOR, LLVM_VERSION_MINOR - The major and minor LLVM version
*numbers*.
LLVM_VERSION_BRANCH - The LLVM branch. The intent is for this to be blank
for released versions or "svn".
LLVM_API_VERSION - An arbitrary number identifying the API version.

The purpose of these macros is to support clients who wish to be able to
compile with different versions of LLVM. We currently have no defines to
support this.

The macros are defined in the configure script and need to be manually
updated. They are adjacent to the other code which needs to be manually
updated; my autoconf foo is not sophisticated enough to derive them from the
version string.

The API_VERSION is designed to support this behavior at a finer grained
level than releases. Its success depends on a cooperative policy where API
changes imply a  bump of this value. I believe Tanya has encourage
developers to clearly mark what are API changes, with limited success.
Making LLVM_API_VERSION successful requires people (or reviewers) to
actively (a) recognize when they make an API change, and (b) bump the value.

Although this requires a bit more care, this has the following benefits:
(1) API changes are clearly marked; they are commits which update
LLVM_API_VERSION.

(2) Reviewing API changes between releases is simplified, the revision log
for Version.h can be consulted.

(3) Clients gain additional flexibility in tracking TOT. This has been
important for me in the past on the klee project, where I would like to run
with a known good LLVM version, but occasionally will test TOT in order to
roll that known good version forward. This has historically been a pain
since I need to update my code to work with TOT, test it, then roll back my
changes if there are issues.

The LLVM_VERSION_* macros are necessary in my opinion. The LLVM_API_VERSION
macro can be argued separately if it has opponents.

 - Daniel
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