[PATCH] D37131: [coroutines] Support coroutine-handle returning await-suspend (i.e symmetric control transfer)

[Gor Nishanov via Phabricator via cfe-commits]

GorNishanov created this revision.

If await_suspend returns a coroutine_handle, as in the example below:

  coroutine_handle<> await_suspend(coroutine_handle<> h) {
    coro.promise().waiter = h;
    return coro;
  }

suspensionExpression processing will resume the coroutine pointed at by that handle.
Related LLVM change https://reviews.llvm.org/rL311751 makes resume calls of this kind `musttail` at any optimization level.

This enables unlimited symmetric control transfer from coroutine to coroutine without blowing up the stack.


https://reviews.llvm.org/D37131

Files:
  lib/CodeGen/CGCoroutine.cpp
  lib/Sema/SemaCoroutine.cpp
  test/CodeGenCoroutines/coro-await.cpp

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