[llvm] Add missing return on nullptr check (PR #92125)

[Jon Roelofs via llvm-commits]

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@@ -3392,8 +3392,10 @@ static bool HandleUse(TreePattern &I, TreePatternNodePtr Pat,
   Record *Rec;
   if (Pat->isLeaf()) {
     DefInit *DI = dyn_cast<DefInit>(Pat->getLeafValue());
-    if (!DI)
+    if (!DI) {
       I.error("Input $" + Pat->getName() + " must be an identifier!");
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jroelofs wrote:

Mind adding a test that covers this error message? ubsan'd builds of llvm would have caught this if we had one.

https://github.com/llvm/llvm-project/pull/92125