David Majnemer a252138942 InstCombine: Don't miscompile (x lshr C1) udiv C2 ...

We have a transform that changes:
  (x lshr C1) udiv C2
into:
  x udiv (C2 << C1)

However, it is unsafe to do so if C2 << C1 discards any of C2's bits.

This fixes PR21255.

llvm-svn: 219634

2014-10-13 21:48:30 +00:00

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