[all-commits] [llvm/llvm-project] 7ae5d0: Fix a stack overflow in ScalarEvolution.

[Johannes Reifferscheid via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 7ae5d00afaf39fae78e411cb44f665e1dc52b356
      https://github.com/llvm/llvm-project/commit/7ae5d00afaf39fae78e411cb44f665e1dc52b356
  Author: Johannes Reifferscheid <jreiffers at google.com>
  Date:   2022-08-03 (Wed, 03 Aug 2022)

  Changed paths:
    M llvm/lib/Analysis/ScalarEvolution.cpp

  Log Message:
  -----------
  Fix a stack overflow in ScalarEvolution.

Unfortunately, this overflow is extremely hard to reproduce reliably (in fact, I was unable to do so). The issue is that:

- getOperandsToCreate sometimes skips creating an SCEV for the LHS
- then, createSCEV is called for the BinaryOp
- ... which calls getNoWrapFlagsFromUB
- ... which under certain circumstances calls isSCEVExprNeverPoison
- ... which under certain circumstances requires the SCEVs of all operands

For certain deep dependency trees, this causes a stack overflow.

Reviewed By: bkramer, fhahn

Differential Revision: https://reviews.llvm.org/D129745