[PATCH] D30890: Post-dom fix - connect virtual edges to last reverse-reachable BB

[Tobias Grosser via Phabricator via llvm-commits]

grosser added a comment.

Here an example that illustrates the difference between the original patch Daniel proposed in https://reviews.llvm.org/D29705 and the slightly modified one we prose her:

Daniel's patch
==============

Inorder PostDominator Tree:

  [1]  <<exit node>> {0,19}
    [2] %"4" {1,4}
      [3] %"3" {2,3}
    [2] %"1" {5,8}
      [3] %"0" {6,7}
    [2] %"6" {9,18}
      [3] %"12" {10,11}
      [3] %"5" {12,15}
        [4] %"2" {13,14}
      [3] %"11" {16,17}

F3141733: infinite_loop_2-with-daniels-patch.png <https://reviews.llvm.org/F3141733>

This patch
==========

  [1]  <<exit node>> {0,19}
    [2] %"4" {1,18}
      [3] %"3" {2,17}
        [4] %"1" {3,16}
          [5] %"0" {4,5}
          [5] %"6" {6,15}
            [6] %"12" {7,8}
            [6] %"5" {9,12}
              [7] %"2" {10,11}
            [6] %"11" {13,14}

F3141735: infinite_loop_2-with-patch.png <https://reviews.llvm.org/F3141735>

The main difference is that %1 still post-dominates %2 and all the other basic blocks in the reverse-unreachable region. This behavior only requires


https://reviews.llvm.org/D30890