Benjamin Kramer 6cf07a80ff Teach SCEV's icmp simplification logic that a-b == 0 is equivalent to a == b. ...

This also required making recursive simplifications until
nothing changes or a hard limit (currently 3) is hit.

With the simplification in place indvars can canonicalize
loops of the form
for (unsigned i = 0; i < a-b; ++i)
into
for (unsigned i = 0; i != a-b; ++i)
which used to fail because SCEV created a weird umax expr
for the backedge taken count.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157701 91177308-0d34-0410-b5e6-96231b3b80d8

2012-05-30 18:32:23 +00:00

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