[llvm] [MIR] Replace bespoke DIExpression parser (PR #96827)

[Orlando Cazalet-Hyams via llvm-commits]

================
@@ -224,3 +225,19 @@ Type *llvm::parseTypeAtBeginning(StringRef Asm, unsigned &Read,
     return nullptr;
   return Ty;
 }
+
+DIExpression *llvm::parseDIExpressionAtBeginning(StringRef Asm, unsigned &Read,
+                                                 SMDiagnostic &Err,
+                                                 const Module &M,
+                                                 const SlotMapping *Slots) {
+  SourceMgr SM;
+  std::unique_ptr<MemoryBuffer> Buf = MemoryBuffer::getMemBuffer(Asm);
+  SM.AddNewSourceBuffer(std::move(Buf), SMLoc());
+  MDNode *MD;
+  if (LLParser(Asm, SM, Err, const_cast<Module *>(&M), nullptr, M.getContext())
+          .parseDIExpressionAtBeginning(MD, Read, Slots))
+    return nullptr;
+  if (auto *Expr = dyn_cast<DIExpression>(MD))
+    return Expr;
+  return nullptr;
----------------
OCHyams wrote:

```suggestion
  return dyn_cast<DIExpression>(MD);
```

https://github.com/llvm/llvm-project/pull/96827