[MIRParser][nfc] Factor out code parsing debug MD nodes

[fdeazeve]

Summary

This commit splits a function that both parses MD nodes from YAML into
DI{Expr,Loc,Variable} objects AND adds an entry to the MF variable table, so
that each of those jobs is done separately.

It will enable subsequent patches to reuse the MD node parsing code.

[fdeazeve]

Since this is a fairly straightforward NFC patch, I'll go ahead and merge it. Happy to address any concerns afterwards.

llvm/lib/CodeGen/MIRParser/MIRParser.cpp

public:
   bool initializeCallSiteInfo(PerFunctionMIParsingState &PFS,
                               const yaml::MachineFunction &YamlMF);
 
   bool parseCalleeSavedRegister(PerFunctionMIParsingState &PFS,
                                 std::vector<CalleeSavedInfo> &CSIInfo,
                                 const yaml::StringValue &RegisterSource,
                                 bool IsRestored, int FrameIdx);
 
+  struct VarExprLoc {
+    DILocalVariable *DIVar = nullptr;
+    DIExpression *DIExpr = nullptr;
+    DILocation *DILoc = nullptr;
+  };
+
+  std::optional<VarExprLoc> parseVarExprLoc(PerFunctionMIParsingState &PFS,
+                                            const yaml::StringValue &VarStr,
+                                            const yaml::StringValue &ExprStr,
+                                            const yaml::StringValue &LocStr);
   template <typename T>
   bool parseStackObjectsDebugInfo(PerFunctionMIParsingState &PFS,
                                   const T &Object,
                                   int FrameIdx);
 
   bool initializeConstantPool(PerFunctionMIParsingState &PFS,
                               MachineConstantPool &ConstantPool,
                               const yaml::MachineFunction &YamlMF);
static bool typecheckMDNode(T *&Result, MDNode *Node,
   Result = dyn_cast<T>(Node);
   if (!Result)
     return Parser.error(Source.SourceRange.Start,
                         "expected a reference to a '" + TypeString +
                             "' metadata node");
   return false;
 }
 
+std::optional<MIRParserImpl::VarExprLoc> MIRParserImpl::parseVarExprLoc(
+    PerFunctionMIParsingState &PFS, const yaml::StringValue &VarStr,
+    const yaml::StringValue &ExprStr, const yaml::StringValue &LocStr) {
+  MDNode *Var = nullptr;
+  MDNode *Expr = nullptr;
+  MDNode *Loc = nullptr;
+  if (parseMDNode(PFS, Var, VarStr) || parseMDNode(PFS, Expr, ExprStr) ||
+      parseMDNode(PFS, Loc, LocStr))
+    return std::nullopt;
+  DILocalVariable *DIVar = nullptr;
+  DIExpression *DIExpr = nullptr;
+  DILocation *DILoc = nullptr;
+  if (typecheckMDNode(DIVar, Var, VarStr, "DILocalVariable", *this) ||
+      typecheckMDNode(DIExpr, Expr, ExprStr, "DIExpression", *this) ||
+      typecheckMDNode(DILoc, Loc, LocStr, "DILocation", *this))
+    return std::nullopt;
+  return VarExprLoc{DIVar, DIExpr, DILoc};
+}
+
 template <typename T>
 bool MIRParserImpl::parseStackObjectsDebugInfo(PerFunctionMIParsingState &PFS,
                                                const T &Object, int FrameIdx) {
+  std::optional<VarExprLoc> MaybeInfo =
+      parseVarExprLoc(PFS, Object.DebugVar, Object.DebugExpr, Object.DebugLoc);
+  if (!MaybeInfo)
+    return true;
   // Debug information can only be attached to stack objects; Fixed stack
   // objects aren't supported.
-  MDNode *Var = nullptr, *Expr = nullptr, *Loc = nullptr;
-  if (parseMDNode(PFS, Var, Object.DebugVar) ||
-      parseMDNode(PFS, Expr, Object.DebugExpr) ||
-      parseMDNode(PFS, Loc, Object.DebugLoc))
-    return true;
-  if (!Var && !Expr && !Loc)
-    return false;
-  DILocalVariable *DIVar = nullptr;
-  DIExpression *DIExpr = nullptr;
-  DILocation *DILoc = nullptr;
-  if (typecheckMDNode(DIVar, Var, Object.DebugVar, "DILocalVariable", *this) ||
-      typecheckMDNode(DIExpr, Expr, Object.DebugExpr, "DIExpression", *this) ||
-      typecheckMDNode(DILoc, Loc, Object.DebugLoc, "DILocation", *this))
-    return true;
-  PFS.MF.setVariableDbgInfo(DIVar, DIExpr, FrameIdx, DILoc);
+  if (MaybeInfo->DIVar || MaybeInfo->DIExpr || MaybeInfo->DILoc)
+    PFS.MF.setVariableDbgInfo(MaybeInfo->DIVar, MaybeInfo->DIExpr, FrameIdx,
+                              MaybeInfo->DILoc);
   return false;
 }
 
 bool MIRParserImpl::parseMDNode(PerFunctionMIParsingState &PFS,
     MDNode *&Node, const yaml::StringValue &Source) {
   if (Source.Value.empty())
     return false;
   SMDiagnostic Error;