[SCEV] See through op.with.overflow intrinsics (re-apply)
Summary:
This change teaches SCEV to see reduce `(extractvalue
0 (op.with.overflow X Y))` into `op X Y` (with a no-wrap tag if
possible).
This was first checked in at r265912 but reverted in r265950 because it
exposed some issues around how SCEV handled post-inc add recurrences.
Those issues have now been fixed.
Reviewers: atrick, regehr
Subscribers: mcrosier, mzolotukhin, llvm-commits
Differential Revision: http://reviews.llvm.org/D18684
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@271152
91177308-0d34-0410-b5e6-
96231b3b80d8
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