Tim Northover 01b4aa9437 ARM: tell LLVM about zext properties of ldrexb/ldrexh ...

Implementing this via ComputeMaskedBits has two advantages:
  + It actually works. DAGISel doesn't deal with the chains properly
    in the previous pattern-based solution, so they never trigger.
  + The information can be used in other DAG combines, as well as the
    trivial "get rid of truncs". For example if the trunc is in a
    different basic block.

rdar://problem/16227836

llvm-svn: 205540

2014-04-03 15:10:35 +00:00

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