Michael Zolotukhin 4b4709686d [LoopSimplify] Rebuild LCSSA for the inner loop after separating nested loops.
Summary:
This hopefully fixes PR28825. The problem now was that a value from the
original loop was used in a subloop, which became a sibling after separation.
While a subloop doesn't need an lcssa phi node, a sibling does, and that's
where we broke LCSSA. The most natural way to fix this now is to simply call
formLCSSA on the original loop: it'll do what we've been doing before plus
it'll cover situations described above.

I think we don't need to run formLCSSARecursively here, and we have an assert
to verify this (I've tried testing it on LLVM testsuite + SPECs). I'd be happy
to be corrected here though.

I also changed a run line in the test from '-lcssa -loop-unroll' to
'-lcssa -loop-simplify -indvars', because it exercises LCSSA
preservation to the same extent, but also makes less unrelated
transformation on the CFG, which makes it easier to verify.

Reviewers: chandlerc, sanjoy, silvas

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D23288

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278173 91177308-0d34-0410-b5e6-96231b3b80d8
2016-08-09 22:44:56 +00:00
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