[LoopUnroll] Avoid UB when converting from WeakVH to `Value *`

Calling `operator*` on a WeakVH with a null value yields a null
reference, which is UB. Avoid this by implicitly converting the WeakVH
to a `Value *` rather than dereferencing and then taking the address
for the type conversion.

Differential Revision: https://reviews.llvm.org/D73280

1 files changed, 4 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 4b94b37..bb0b6ed 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -207,10 +207,11 @@ void llvm::simplifyLoopAfterUnroll(Loop *L, bool SimplifyIVs, LoopInfo *LI,
 
     // Aggressively clean up dead instructions that simplifyLoopIVs already
     // identified. Any remaining should be cleaned up below.
-    while (!DeadInsts.empty())
-      if (Instruction *Inst =
-              dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
+    while (!DeadInsts.empty()) {
+      Value *V = DeadInsts.pop_back_val();
+      if (Instruction *Inst = dyn_cast_or_null<Instruction>(V))
         RecursivelyDeleteTriviallyDeadInstructions(Inst);
+    }
   }
 
   // At this point, the code is well formed.  We now do a quick sweep over the