[all-commits] [llvm/llvm-project] 24cde2: [SCEV] Remove invariant requirement from isSCEVExp...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 24cde2f6023a765b66923f4a4ac033a91878b856
      https://github.com/llvm/llvm-project/commit/24cde2f6023a765b66923f4a4ac033a91878b856
  Author: Philip Reames <listmail at philipreames.com>
  Date:   2021-10-01 (Fri, 01 Oct 2021)

  Changed paths:
    M llvm/lib/Analysis/ScalarEvolution.cpp
    M llvm/test/Analysis/ScalarEvolution/flags-from-poison.ll

  Log Message:
  -----------
  [SCEV] Remove invariant requirement from isSCEVExprNeverPoison

This code is attempting to prove that I must execute if we enter the defining scope of the SCEV which will be created from I. In the case where it found a defining addrec scope, it had a rather odd restriction that all of the other operands must be loop invariant in that addrec's loop.

As near as I can tell here, we really only need a upper bound on the defining scope. If we can prove the stronger property, then we must also have proven the property on the exact defining scope as well.

In practice, the actual effect of this change is narrow. The compile time restriction at the top of the routine basically limits us to I being an arithmetic in some loop L with both an addrec operand in L, and a unknown operands in L. Possible to demonstrate, but the main value of the change is removing unneeded code.

Differential Revision: https://reviews.llvm.org/D110892