[llvm] [llvm] Fix possible null dereference in Transforms/Scalar (PR #157461)

[Nikita Popov via llvm-commits]

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@@ -521,7 +521,7 @@ struct MainSwitch {
 
     Instruction *SIUse = dyn_cast<Instruction>(SI->user_back());
     // The use of the select inst should be either a phi or another select.
-    if (!SIUse && !(isa<PHINode>(SIUse) || isa<SelectInst>(SIUse)))
+    if (SIUse && !(isa<PHINode>(SIUse) || isa<SelectInst>(SIUse)))
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nikic wrote:

I'm pretty sure this was supposed to be:
```suggestion
    if (!SIUse || !(isa<PHINode>(SIUse) || isa<SelectInst>(SIUse)))
```

https://github.com/llvm/llvm-project/pull/157461