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In searching for a fix for the underlying code-quality bug highlighted by r246937 (that SDAG simplification can lead to us generating an ISD::OR node with a constant zero LHS), I ran across this: We generically canonicalize commutative binary-operation nodes in SDAG getNode so that, if only one operand is a constant, it will be on the RHS. However, we were doing this only after a bunch of constant-based simplification checks that all assume this canonical form (that any constant will be on the RHS). Moving the operand-swapping canonicalization prior to these checks seems like the right thing to do (and, as it turns out, causes SDAG to completely fold away the computation in test/CodeGen/ARM/2012-11-14-subs_carry.ll, just like InstCombine would do). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246938 91177308-0d34-0410-b5e6-96231b3b80d8
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