[PATCH] D138814: [InstCombine] Combine a/lshr of add -> uadd.with.overflow

[Pierre van Houtryve via Phabricator via llvm-commits]

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Tries to perform

  (Xshr (add (zext a, i2^n), (zext b, i2^n)), 2^(n-1))
    -> (llvm.uadd.with.overflow a, b).overflow
  where
    - Xshr can be ashr or lshr
    - a and b has type i2^(n-1).

This seems to be a pattern that just comes from OpenCL front-ends, so adding DAG/GISel combines doesn't seem to be worth the complexity.

Original patch D107552 <https://reviews.llvm.org/D107552> by @abinavpp
Resolves issue raised on ROCm repo: https://github.com/RadeonOpenCompute/ROCm/issues/488


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D138814

Files:
  llvm/lib/Transforms/InstCombine/InstCombineInternal.h
  llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
  llvm/test/Transforms/InstCombine/shift-add.ll

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