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[IndVars] Fix corner case with unreachable Phi inputs. PR40454

Authored by mkazantsev on Feb 11 2019, 4:02 AM.



Logic in getInsertPointForUses doesn't account for a corner case when Def only
comes to a Phi user from unreachable blocks. In this case, the incoming value may
be arbitrary (and not even available in the input block) and break the loop-related
invariants that are asserted below.

In fact, if we encounter this situation, no IR modification is needed. This Phi will be
simplified away with nearest cleanup.

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Event Timeline

mkazantsev created this revision.Feb 11 2019, 4:02 AM
spatel accepted this revision.Feb 11 2019, 12:50 PM

I'm not familiar with this code, but the change is strictly safer, so LGTM.
You may want to wait a bit before committing in case there are any other comments.

This revision is now accepted and ready to land.Feb 11 2019, 12:50 PM

Moved print after check.

This revision was automatically updated to reflect the committed changes.
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