[PATCH] InstCombine: Combine two icmps into one if the RHSs agree

[David Majnemer]

Hi nicholas, bkramer,

consider:
%cmp1 = icmp CC %V1, C
%cmp2 = icmp CC %V2, C
%and  = and %cmp1, %cmp2

we can transform this into:
%or  = or %V1, %V2
%cmp = icmp CC %or, C

This saves us an instruction and generates considerably nicer assembly
for X86, X86-64, arm, powerpc64 and aarch64.

http://reviews.llvm.org/D4744

Files:
  lib/Transforms/InstCombine/InstCombine.h
  lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  test/Transforms/InstCombine/2008-08-05-And.ll
  test/Transforms/InstCombine/or.ll
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