[Attributor][FIX] Avoid dangling value pointers during code modification

When we replace instructions with unreachable we delete instructions. We
now avoid dangling pointers to those deleted instructions in the
`ToBeChangedToUnreachableInsts` set. Other modification collections
might need to be updated in the future as well.

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index 13fcf6aa724..b3b9e1e185a 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -5668,8 +5668,9 @@ ChangeStatus Attributor::run(Module &M) {
         }
       }
     }
-    for (Instruction *I : ToBeChangedToUnreachableInsts)
-      changeToUnreachable(I, /* UseLLVMTrap */ false);
+    for (auto &V : ToBeChangedToUnreachableInsts)
+      if (Instruction *I = dyn_cast_or_null<Instruction>(V))
+        changeToUnreachable(I, /* UseLLVMTrap */ false);
     for (Instruction *I : TerminatorsToFold)
       ConstantFoldTerminator(I->getParent());