[clang-tools-extra] Clean up strange uses of getAnalysisIfAvailable (PR #65729)

[Jay Foad via cfe-commits]

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@@ -3280,7 +3280,7 @@ class llvm::gvn::GVNLegacyPass : public FunctionPass {
     if (skipFunction(F))
       return false;
 
-    auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
+    auto &LIWP = getAnalysis<LoopInfoWrapperPass>();
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jayfoad wrote:

I prefer not to leave it as is - I think either we should get the analysis with `getAnalysis` or we should remove the `addRequired`, so that they are consistent with each other.

https://github.com/llvm/llvm-project/pull/65729