[PATCH] D140509: [DAGCombiner] Pre-promote (zext (abs X)) to (abs (sext X)) when X has an illegal type.

[Craig Topper via Phabricator via llvm-commits]

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Type legalization will insert a sign extend anyway. By doing it
early we can remove the zext. ComputeNumSignBits can't spot it
after type legalization because type legalization may expand
the abs to sra+xor+sub.

If the zext result type is larger than the type to be promoted to
we'll promote to a legal type and then zext the rest of the way.
If the legal type is larger than the destination type we can promote
and then truncate.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140509

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/RISCV/iabs.ll

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