[all-commits] [llvm/llvm-project] 99d258: [ScalarEvolution] Handle <= and >= in non infinite...

[William Moses via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 99d2582164c4bc8f10c3e3c20dd3690243ad49ba
      https://github.com/llvm/llvm-project/commit/99d2582164c4bc8f10c3e3c20dd3690243ad49ba
  Author: William S. Moses <gh at wsmoses.com>
  Date:   2022-01-28 (Fri, 28 Jan 2022)

  Changed paths:
    M llvm/include/llvm/Analysis/ScalarEvolution.h
    M llvm/lib/Analysis/ScalarEvolution.cpp
    A llvm/test/Analysis/ScalarEvolution/finite-trip-count.ll

  Log Message:
  -----------
  [ScalarEvolution] Handle <= and >= in non infinite loops

Extend scalar evolution to handle >= and <= if a loop is known to be finite and the induction variable guards the condition. Specifically, with these assumptions lhs <= rhs is equivalent to lhs < rhs + 1 and lhs >= rhs to lhs > rhs -1.

In the case of lhs <= rhs, this is true since the only case these are not equivalent
is when rhs == unsigned/signed intmax, which would have resulted in an infinite loop.

In the case of lhs >= rhs, this is true since the only case these are not equivalent
is when rhs == unsigned/signed intmin, which would again have resulted in an infinite loop.

Reviewed By: lebedev.ri

Differential Revision: https://reviews.llvm.org/D118090