Chris Lattner e0e4cc7fd5 Teach instcombine's sext elimination logic to be more aggressive.
Previously, instcombine would only promote an expression tree to
the larger type if doing so eliminated two casts.  This is because
a need to manually do the sign extend after the promoted expression
tree with two shifts.  Now, we keep track of whether the result of
the computation is going to be properly sign extended already.  If
so, we can unconditionally promote the expression, which allows us
to zap more sext's.

This implements rdar://6598839 (aka gcc pr38751)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92815 91177308-0d34-0410-b5e6-96231b3b80d8
2010-01-06 01:56:21 +00:00
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2009-12-23 20:13:44 +00:00
2010-01-05 17:55:26 +00:00