[MC] Make ELFEntrySizeMap a DenseMap

llvm/include/llvm/MC/MCContext.h

@@ -391,29 +391,13 @@ class MCContext {
   /// Map of currently defined macros.
   StringMap<MCAsmMacro> MacroMap;
 
-  struct ELFEntrySizeKey {
-    std::string SectionName;
-    unsigned Flags;
-    unsigned EntrySize;
-
-    ELFEntrySizeKey(StringRef SectionName, unsigned Flags, unsigned EntrySize)
-        : SectionName(SectionName), Flags(Flags), EntrySize(EntrySize) {}
-
-    bool operator<(const ELFEntrySizeKey &Other) const {
-      if (SectionName != Other.SectionName)
-        return SectionName < Other.SectionName;
-      if (Flags != Other.Flags)
-        return Flags < Other.Flags;
-      return EntrySize < Other.EntrySize;
-    }
-  };
-
   // Symbols must be assigned to a section with a compatible entry size and
   // flags. This map is used to assign unique IDs to sections to distinguish
   // between sections with identical names but incompatible entry sizes and/or
   // flags. This can occur when a symbol is explicitly assigned to a section,
-  // e.g. via __attribute__((section("myname"))).
-  std::map<ELFEntrySizeKey, unsigned> ELFEntrySizeMap;
+  // e.g. via __attribute__((section("myname"))). The map key is the tuple
+  // (section name, flags, entry size).
+  DenseMap<std::tuple<StringRef, unsigned, unsigned>, unsigned> ELFEntrySizeMap;
 
   // This set is used to record the generic mergeable section names seen.
   // These are sections that are created as mergeable e.g. .debug_str. We need

llvm/lib/MC/MCContext.cpp

@@ -620,15 +620,20 @@ void MCContext::recordELFMergeableSectionInfo(StringRef SectionName,
                                               unsigned Flags, unsigned UniqueID,
                                               unsigned EntrySize) {
   bool IsMergeable = Flags & ELF::SHF_MERGE;
-  if (UniqueID == GenericSectionID)
+  if (UniqueID == GenericSectionID) {
     ELFSeenGenericMergeableSections.insert(SectionName);
+    // Minor performance optimization: avoid hash map lookup in
+    // isELFGenericMergeableSection, which will return true for SectionName.
+    IsMergeable = true;
+  }
 
   // For mergeable sections or non-mergeable sections with a generic mergeable
   // section name we enter their Unique ID into the ELFEntrySizeMap so that
   // compatible globals can be assigned to the same section.
+
   if (IsMergeable || isELFGenericMergeableSection(SectionName)) {
     ELFEntrySizeMap.insert(std::make_pair(
-        ELFEntrySizeKey{SectionName, Flags, EntrySize}, UniqueID));
+        std::make_tuple(SectionName, Flags, EntrySize), UniqueID));
   }
 }
 
@@ -645,8 +650,7 @@ bool MCContext::isELFGenericMergeableSection(StringRef SectionName) {
 std::optional<unsigned>
 MCContext::getELFUniqueIDForEntsize(StringRef SectionName, unsigned Flags,
                                     unsigned EntrySize) {
-  auto I = ELFEntrySizeMap.find(
-      MCContext::ELFEntrySizeKey{SectionName, Flags, EntrySize});
+  auto I = ELFEntrySizeMap.find(std::make_tuple(SectionName, Flags, EntrySize));
   return (I != ELFEntrySizeMap.end()) ? std::optional<unsigned>(I->second)
                                       : std::nullopt;
 }