[PATCH] D46340: AMDGPU/SI: Handle infinite loop for the structurizer to work with CFG with infinite loops.

[Changpeng Fang via Phabricator via llvm-commits]

cfang marked an inline comment as done.
cfang added a comment.

In https://reviews.llvm.org/D46340#1086444, @nhaehnle wrote:

> So this does not cover all possible cases of "irreducible" infinite loops, e.g. consider the case with basic blocks A and B where both end with a conditional branch that can go to either A or B. I.e., there are no unconditional branches in the loop.
>
> A more robust approach would be to also transform conditional branches like this:
>
>   br i1 %cc, label %A, label %B
>   
>
> becomes
>
>     br i1 true, label %DummyReturnBB, label %local_dummy
>   local_dummy:
>     br i1 %cc, label %A, label %b
>


Thank you so much for pointing out this case and providing the algorithm. Done as suggested.



================
Comment at: lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp:194
+        ConstantInt *BoolTrue = ConstantInt::getTrue(F.getContext());
+        BB->getInstList().pop_back(); // Remove the unconditional branch.
+        // Add a new conditional branch with a dummy edge to the return block.
----------------
nhaehnle wrote:
> Shouldn't this use eraseFromParent()?
Right. There are other places in the same file need to do the same thing using eraseFromParent(). Will do in a separate patch.


https://reviews.llvm.org/D46340