[PATCH] D137936: [AArch64] Optimize cmp chain when the result is tested for [in]equality with 0

[Allen zhong via Phabricator via llvm-commits]

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- For case bcmp9, there is extras AND and EXTEND int the chain of OR/XOR, which prevent the transform, so we address it with following steps: a) Fold AND + any_extend -> zero_extend in Optimized type-legalized selection DAG b) extend the isOrXorChain to address the ZERO_EXTEND

- The key IR frag related: t37: i32,ch = load<(load (s8) from %ir.4), anyext from i8> t0, t11, undef:i64 t12: i64 = add t4, Constant:i64<8> t38: i32,ch = load<(load (s8) from %ir.5), anyext from i8> t0, t12, undef:i64 t39: i32 = xor t37, t38 t40: i64 = any_extend t39 t42: i64 = and t40, Constant:i64<255>


https://reviews.llvm.org/D137936

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
  llvm/test/CodeGen/AArch64/bcmp.ll

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