[PATCH] D122915: [AArch64] UBFM fold in the MIPeepholeOpt.

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

It looks like the lsr+bfi is coming out of tryBitfieldInsertOpFromOr in AArch64ISelDAGToDAG.cpp.  I see two possible alternatives:

1. Enhance tryBitfieldInsertOpFromOr to detect when it's shifting a shift.
2. Form the BFM op as a DAGCombine, instead of waiting for isel.

This MI peephole seems unlikely to be useful outside of this one case, so I think I'd prefer to fix the existing logic.


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  https://reviews.llvm.org/D122915/new/

https://reviews.llvm.org/D122915