[all-commits] [llvm/llvm-project] 842b4c: [LoopDeletion] Exploit undef Phi inputs when symbo...

[Max Kazantsev via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 842b4c83cb751d5f371ba27881fc92fdbd38d850
      https://github.com/llvm/llvm-project/commit/842b4c83cb751d5f371ba27881fc92fdbd38d850
  Author: Max Kazantsev <mkazantsev at azul.com>
  Date:   2021-06-23 (Wed, 23 Jun 2021)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LoopDeletion.cpp
    M llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll

  Log Message:
  -----------
  [LoopDeletion] Exploit undef Phi inputs when symbolically executing 1st iteration

Follow-up on Roman's idea expressed in D103959.
- If a Phi has undefined inputs from live blocks:
   - and no other inputs, assume it is undef itself;
   - and exactly one non-undef input, we can assume that all undefs are equal to this input.

Differential Revision: https://reviews.llvm.org/D104618
Reviewed By: lebedev.ri, nikic