IRMover: Proper fix of performance regression of llvm#146020 (llvm#157218)

In llvm#157045 I didn't realize that IRMover object is
one for entire LTO, but IRLinker is created per
module. We need one chache for combined module.

I timed "IRLinker::linkNamedMDNodes" code on one
of our internal binaries, not very large, but
above average.

Before llvm#146020: 0.4859s
After llvm#146020: 624.4686s
After llvm#157045: 322.3493s
After this patch: 0.5574s

Author: vitalybuka

llvm/include/llvm/Linker/IRMover.h

@@ -10,6 +10,7 @@
 #define LLVM_LINKER_IRMOVER_H
 
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/FunctionExtras.h"
 #include "llvm/Support/Compiler.h"
@@ -19,6 +20,8 @@ namespace llvm {
 class Error;
 class GlobalValue;
 class Metadata;
+class MDNode;
+class NamedMDNode;
 class Module;
 class StructType;
 class TrackingMDRef;
@@ -67,6 +70,8 @@ class IRMover {
   using LazyCallback =
       llvm::unique_function<void(GlobalValue &GV, ValueAdder Add)>;
 
+  using NamedMDNodesT = DenseMap<const NamedMDNode *, DenseSet<const MDNode *>>;
+
   /// Move in the provide values in \p ValuesToLink from \p Src.
   ///
   /// - \p AddLazyFor is a call back that the IRMover will call when a global
@@ -86,6 +91,7 @@ class IRMover {
   Module &Composite;
   IdentifiedStructTypeSet IdentifiedStructTypes;
   MDMapT SharedMDs; ///< A Metadata map to use for all calls to \a move().
+  NamedMDNodesT NamedMDNodes; ///< Cache for IRMover::linkNamedMDNodes().
 };
 
 } // End llvm namespace

llvm/lib/Linker/IRMover.cpp

@@ -293,7 +293,7 @@ class IRLinker {
   std::unique_ptr<Module> SrcM;
 
   // Lookup table to optimize IRMover::linkNamedMDNodes().
-  DenseMap<StringRef, DenseSet<MDNode *>> NamedMDNodes;
+  IRMover::NamedMDNodesT &NamedMDNodes;
 
   /// See IRMover::move().
   IRMover::LazyCallback AddLazyFor;
@@ -440,10 +440,12 @@ class IRLinker {
   IRLinker(Module &DstM, MDMapT &SharedMDs,
            IRMover::IdentifiedStructTypeSet &Set, std::unique_ptr<Module> SrcM,
            ArrayRef<GlobalValue *> ValuesToLink,
-           IRMover::LazyCallback AddLazyFor, bool IsPerformingImport)
-      : DstM(DstM), SrcM(std::move(SrcM)), AddLazyFor(std::move(AddLazyFor)),
-        TypeMap(Set), GValMaterializer(*this), LValMaterializer(*this),
-        SharedMDs(SharedMDs), IsPerformingImport(IsPerformingImport),
+           IRMover::LazyCallback AddLazyFor, bool IsPerformingImport,
+           IRMover::NamedMDNodesT &NamedMDNodes)
+      : DstM(DstM), SrcM(std::move(SrcM)), NamedMDNodes(NamedMDNodes),
+        AddLazyFor(std::move(AddLazyFor)), TypeMap(Set),
+        GValMaterializer(*this), LValMaterializer(*this), SharedMDs(SharedMDs),
+        IsPerformingImport(IsPerformingImport),
         Mapper(ValueMap, RF_ReuseAndMutateDistinctMDs | RF_IgnoreMissingLocals,
                &TypeMap, &GValMaterializer),
         IndirectSymbolMCID(Mapper.registerAlternateMappingContext(
@@ -1138,7 +1140,7 @@ void IRLinker::linkNamedMDNodes() {
 
     NamedMDNode *DestNMD = DstM.getOrInsertNamedMetadata(NMD.getName());
 
-    auto &Inserted = NamedMDNodes[DestNMD->getName()];
+    auto &Inserted = NamedMDNodes[DestNMD];
     if (Inserted.empty()) {
       // Must be the first module, copy everything from DestNMD.
       Inserted.insert(DestNMD->operands().begin(), DestNMD->operands().end());
@@ -1683,6 +1685,6 @@ Error IRMover::move(std::unique_ptr<Module> Src,
                     LazyCallback AddLazyFor, bool IsPerformingImport) {
   IRLinker TheIRLinker(Composite, SharedMDs, IdentifiedStructTypes,
                        std::move(Src), ValuesToLink, std::move(AddLazyFor),
-                       IsPerformingImport);
+                       IsPerformingImport, NamedMDNodes);
   return TheIRLinker.run();
 }