[PATCH] D130142: [Coroutines] Introduce @llvm.coro.tls.wrapper to block optimizations

[Yuanfang Chen via Phabricator via llvm-commits]

ychen added a comment.

In D130142#3667280 <https://reviews.llvm.org/D130142#3667280>, @ChuanqiXu wrote:

> In D130142#3666355 <https://reviews.llvm.org/D130142#3666355>, @ychen wrote:
>
>> John mentioned this test case,
>>
>>   thread_local int x = 0;
>>   void helper(int *x, int y);
>>   my_coro coroutine() {
>>     helper(&x, co_await something_suspending());
>>   }
>>
>> Is replacing the TLS variable with `llvm.coro.tls.wrapper` in CoroEarly too late to fix the issue?
>
> This example may be fine since C++ standard specifies that the order of evaluation of function arguments is unspecified: https://en.cppreference.com/w/cpp/language/eval_order.

That's my understanding as well. Sorry I should've changed it a little,

  thread_local int x = 0;
  void helper(int *x, int y);
  my_coro coroutine() {
    helper(&x, (&x, co_await something_suspending()));
  }

The comma operator should have the left-to-right evaluation order. Personally, I hope there is a workaround for Clang 15. I'm just trying to convince myself that this workaround solves both issues in principle (even with potential pessimization with the TLS variables). But this test case makes me hesitate.


Repository:
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  https://reviews.llvm.org/D130142/new/

https://reviews.llvm.org/D130142