[PATCH] D154565: [InstCombine] Fold icmps comparing uadd_sat with a constant

[Dhruv Chawla via Phabricator via llvm-commits]

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This patch is a continuation of D154206 <https://reviews.llvm.org/D154206>. It introduces a fold for the
operation "uadd_sat(X, C) pred C2" where "C" and "C2" are constants. The
fold is:

uadd_sat(X, C) pred C2

> (X >= ~C) || ((X + C) pred C2) -> when (UINT_MAX pred C2) is true
===================================================================

> (X < ~C)  && ((X + C) pred C2) -> when (UINT_MAX pred C2) is false
====================================================================

These expressions can generally be folded into a simpler expression. As
they can sometimes emit more than one instruction, they are limited to
cases where the "uadd_sat" has only one user.

Proofs: https://alive2.llvm.org/ce/z/wWeirP


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D154565

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/icmp-uadd-sat.ll
  llvm/test/Transforms/InstCombine/icmp-usub-sat.ll

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