[llvm] [LowerSwitch] Don't let pass manager handle the dependency (PR #68662)

[Arthur Eubanks via llvm-commits]

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@@ -192,6 +191,9 @@ BasicBlock *AMDGPUUnifyDivergentExitNodesImpl::unifyReturnBlockSet(
 bool AMDGPUUnifyDivergentExitNodesImpl::run(Function &F, DominatorTree *DT,
                                             const PostDominatorTree &PDT,
                                             const UniformityInfo &UA) {
+  for (auto &BB : F)
+    assert(hasOnlySimpleTerminator(&BB));
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aeubanks wrote:

should be something like `assert(hasOnlySimpleTerminator(&BB) && "Need to run lower-switch");` so people know what to do if the assert fires

https://github.com/llvm/llvm-project/pull/68662