[XRay] Lazily compute MachineLoopInfo instead of requiring it.
Summary:
Currently X-Ray Instrumentation pass has a dependency on MachineLoopInfo
(and thus on MachineDominatorTree as well) and we have to compute them
even if X-Ray is not used. This patch changes it to a lazy computation
to save compile time by avoiding these redundant computations.
Reviewers: dberris, kubamracek
Subscribers: llvm-commits, hiraditya
Differential Revision: https://reviews.llvm.org/D44666
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327999
91177308-0d34-0410-b5e6-
96231b3b80d8
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