[llvm] [indvars] Missing variables at Og: (PR #69920)

[Stephen Tozer via llvm-commits]

================
@@ -607,6 +608,17 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
   llvm::SmallVector<DPValue *, 4> DeadDPValues;
 
   if (ExitBlock) {
+    if (ExitBlock->phis().empty()) {
+      // As the loop is deleted, replace the debug users with the preserved
+      // induction variable final value recorded by the 'indvar' pass.
+      Value *FinalValue = L->getDebugInductionVariableFinalValue();
+      SmallVector<WeakVH> &DbgUsers = L->getDebugInductionVariableDebugUsers();
+      for (WeakVH &DebugUser : DbgUsers)
+        if (DebugUser)
+          dyn_cast<DbgVariableIntrinsic>(DebugUser)->replaceVariableLocationOp(
----------------
SLTozer wrote:

```suggestion
          cast<DbgVariableIntrinsic>(DebugUser)->replaceVariableLocationOp(
```
This should just be a normal `cast` - the idea of `dyn_cast` is that it can return `nullptr` if the cast is unsuccessful, unlike `cast` which just asserts; if you aren't checking the result for `nullptr`, then there's no value in using `dyn_cast` over `cast`. I think in this case, you just want `cast`, since the check above already verifies that the value has not been deleted.

https://github.com/llvm/llvm-project/pull/69920