[all-commits] [llvm/llvm-project] d21660: [Coroutine] Split PHI Nodes in `cleanuppad` blocks...

[Daniel Paoliello via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: d2166076b882e38becf3657ea830ffd2b6a5695e
      https://github.com/llvm/llvm-project/commit/d2166076b882e38becf3657ea830ffd2b6a5695e
  Author: Daniel Paoliello <danpao at microsoft.com>
  Date:   2020-09-25 (Fri, 25 Sep 2020)

  Changed paths:
    M llvm/lib/Transforms/Coroutines/CoroFrame.cpp
    A llvm/test/Transforms/Coroutines/coro-catchswitch-cleanuppad.ll

  Log Message:
  -----------
  [Coroutine] Split PHI Nodes in `cleanuppad` blocks in a way that obeys EH pad rules

Issue Details:
In order to support coroutine splitting, any multi-value PHI node in a coroutine is split into multiple blocks with single-value PHI Nodes, which then allows a subsequent transform to generate `reload` instructions as required (i.e., to reload the value if required if the coroutine has been resumed). This causes issues with EH pads (`catchswitch` and `catchpad`) as all pads within a `catchswitch` must have the same unwind destination, but the coroutine splitting logic may modify them to each have a unique unwind destination if there is a PHI node in the unwind `cleanuppad` that is set from values in the `catchswitch` and `cleanuppad` blocks.

Fix Details:
During splitting, if such a PHI node is detected, then create a "dispatcher" `cleanuppad` as well as the blocks with single-value PHI Nodes: thus the "dispatcher" is the unwind destination and it will detect which predecessor called it and then branch to the appropriate single-value PHI node block, which will then branch back to the original `cleanuppad` block.

Reviewed By: GorNishanov, lxfind

Differential Revision: https://reviews.llvm.org/D88059