Searching all of the existing gc.root implementations I'm aware of (all three of them), there was exactly one use of this mechanism, and that was to implement a performance improvement that should have been applied to the default lowering.
Having this function is requiring a dependency on a CodeGen class (MachineFunction), in a class which is otherwise completely independent of CodeGen. I could solve this differently, but given that I see absolutely no value in preserving this mechanism, I going to just get rid of it.
Note: Tis is the first time I'm intentionally breaking previously supported gc.root functionality. Given 3.6 has branched, I believe this is a good time to do this.
Differential Revision: http://reviews.llvm.org/D7004
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226305 91177308-0d34-0410-b5e6-96231b3b80d8
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