[llvm] [SandboxVectorizer][NFCI] Fix use of possibly-uninitialized scalar. (PR #122201)

[via llvm-commits]

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@@ -700,7 +700,7 @@ Context::CallbackID
 Context::registerCreateInstrCallback(CreateInstrCallback CB) {
   assert(CreateInstrCallbacks.size() <= MaxRegisteredCallbacks &&
          "CreateInstrCallbacks size limit exceeded");
-  CallbackID ID = NextCallbackID++;
+  CallbackID ID{NextCallbackID++};
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vporpo wrote:

same

https://github.com/llvm/llvm-project/pull/122201