[llvm] [PassInstrumentation] Make getPassNameForClassName return optional (PR #150029)

[Nikita Popov via llvm-commits]

================
@@ -165,7 +165,8 @@ class PassInstrumentationCallbacks {
   /// Add a class name to pass name mapping for use by pass instrumentation.
   LLVM_ABI void addClassToPassName(StringRef ClassName, StringRef PassName);
   /// Get the pass name for a given pass class name.
-  LLVM_ABI StringRef getPassNameForClassName(StringRef ClassName);
+  LLVM_ABI std::optional<StringRef>
----------------
nikic wrote:

Just going by the usages, I think it would make things a bit simpler. But no strong opinion, I'm okay with the std::optional as well.

https://github.com/llvm/llvm-project/pull/150029