[PATCH] Revert 221429 and fix bug in TargetLowering::SimplifyDemandedBits

[Gil Rapaport]

Hi Quentin,

I ran lnt w/ spec2006 and didn't witness any related performance degradations. However if you could also run it (for more coverage if you have other externals, and to double-check me) that would be great.

One thing I did notice is that this specific sext-in-reg may be optimized away if left alone: DAGCombiner checks whether the value was already sign extended and drops it (this actually happens in vselect-avx.ll). This suggests that at least on some conditions this X86 optimization is redundant all together, but this requires thorough checking beyond this bug fix.

Thanks,
Gil


http://reviews.llvm.org/D6949

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