[PATCH] D22025: AMDGPU/SI: Do not insert EndCf in an unreachable block

[Matt Arsenault via llvm-commits]

arsenm added inline comments.

================
Comment at: test/CodeGen/AMDGPU/si-annotate-cf-unreachable.ll:30-34
@@ +29,7 @@
+
+bb4:                                              ; preds = %bb3
+  unreachable
+
+bb5:                                              ; preds = %bb3, %bb1
+  unreachable
+}
----------------
cfang wrote:
> arsenm wrote:
> > There should still be another copy of this function with blocks with code (like a volatile store) before the unreachable
> The issue is: for an unreachable block, if we insert EndCf, we will hit "Instruction does not dominate all uses!" assert!
> 
> The "fix" here is actually just a workaround: if there is no instruction before unreachable, we don't insert EndCf.
> 
> If as you suggested there are instructions before unreachable, we will have to insert endCF, and the problem is still there.
> 
> This is a special case in control flow that both "else" and "then" is unreachable. Maybe we need to insert endCF on 
> both paths. 
> 
You check at the insertion point if it is unreachable, not that the block ends in unreachable. That's what I want the other test for, to make sure it doesn't crash in that case. I think what you might really want to be doing is checking for no successors


https://reviews.llvm.org/D22025