[IR] Cache llvm.module.flags metadata in Module

This metadata is queried quite often, so avoiding frequent lookups in
the hash map is beneficial. Therefore, cache the metadata node directly
in the module.

Pull Request: #103410

Author: aengelke

llvm/include/llvm/IR/Module.h

@@ -202,6 +202,9 @@ class LLVM_EXTERNAL_VISIBILITY Module {
                              ///< ID and FunctionType maps to the extension that
                              ///< is used to make the intrinsic name unique.
 
+  /// llvm.module.flags metadata
+  NamedMDNode *ModuleFlags = nullptr;
+
   friend class Constant;
 
 /// @}
@@ -528,7 +531,7 @@ class LLVM_EXTERNAL_VISIBILITY Module {
 
   /// Returns the NamedMDNode in the module that represents module-level flags.
   /// This method returns null if there are no module-level flags.
-  NamedMDNode *getModuleFlagsMetadata() const;
+  NamedMDNode *getModuleFlagsMetadata() const { return ModuleFlags; }
 
   /// Returns the NamedMDNode in the module that represents module-level flags.
   /// If module-level flags aren't found, it creates the named metadata that

llvm/lib/IR/Module.cpp

@@ -272,6 +272,8 @@ NamedMDNode *Module::getOrInsertNamedMetadata(StringRef Name) {
     NMD = new NamedMDNode(Name);
     NMD->setParent(this);
     insertNamedMDNode(NMD);
+    if (Name == "llvm.module.flags")
+      ModuleFlags = NMD;
   }
   return NMD;
 }
@@ -280,6 +282,8 @@ NamedMDNode *Module::getOrInsertNamedMetadata(StringRef Name) {
 /// delete it.
 void Module::eraseNamedMetadata(NamedMDNode *NMD) {
   NamedMDSymTab.erase(NMD->getName());
+  if (NMD == ModuleFlags)
+    ModuleFlags = nullptr;
   eraseNamedMDNode(NMD);
 }
 
@@ -323,17 +327,12 @@ Metadata *Module::getModuleFlag(StringRef Key) const {
   return nullptr;
 }
 
-/// getModuleFlagsMetadata - Returns the NamedMDNode in the module that
-/// represents module-level flags. This method returns null if there are no
-/// module-level flags.
-NamedMDNode *Module::getModuleFlagsMetadata() const {
-  return getNamedMetadata("llvm.module.flags");
-}
-
 /// getOrInsertModuleFlagsMetadata - Returns the NamedMDNode in the module that
 /// represents module-level flags. If module-level flags aren't found, it
 /// creates the named metadata that contains them.
 NamedMDNode *Module::getOrInsertModuleFlagsMetadata() {
+  if (ModuleFlags)
+    return ModuleFlags;
   return getOrInsertNamedMetadata("llvm.module.flags");
 }