[PATCH] D85603: IR: Add convergence control operand bundle and intrinsics

[Simon Moll via Phabricator via llvm-commits]

simoll added inline comments.


================
Comment at: llvm/docs/ConvergentOperations.rst:339-343
+1. Let U be a static controlled convergent operation other than
+   :ref:`llvm.experimental.convergence.loop <llvm.experimental.convergence.loop>`
+   whose convergence token is produced by an instruction D. Two threads
+   executing U execute the same dynamic instance of U if and only if they
+   obtained the token value from the same dynamic instance of D.
----------------
nhaehnle wrote:
> simoll wrote:
> > Should suffice to say that they two threads will execute the same instance if they see the same token value.
> > Above you stated that the token value represents the dynamic instance of the defining instruction.
> No, this is explicitly not sufficient. You can have:
> ```
>   %tok = call token @llvm.experimental.convergence.anchor()
>   br i1 %cc, label %then, label %next
> 
> then:
>   call void @convergent_op() [ "convergencectrl"(token %tok) ]
>   br label %next
> 
> next:
> ```
You mean control could deviate threads? But those threads won't even reach the convergent instruction and only among those that do those that have the same runtime token value will execute it as a pack.


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https://reviews.llvm.org/D85603