[clang] [NFC][Clang][CodeGen] Improve performance for vtable metadata generation (PR #67066)

[Matheus Izvekov via cfe-commits]

https://github.com/mizvekov updated https://github.com/llvm/llvm-project/pull/67066

>From 44d43a8e7fa5b19671bc3f56f934dfb63a632aa4 Mon Sep 17 00:00:00 2001
From: Matheus Izvekov <mizvekov at gmail.com>
Date: Thu, 21 Sep 2023 22:57:27 +0200
Subject: [PATCH] [NFC][Clang][CodeGen] Improve performance for vtable metadata
 generation

Mangle each AddressPoint once, instead of once per comparison.
---
 clang/lib/CodeGen/CGVTables.cpp | 54 ++++++++++++++-------------------
 1 file changed, 22 insertions(+), 32 deletions(-)

diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index d782da2103b4c79..5ec38e0397bf4f7 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -24,6 +24,7 @@
 #include "llvm/Transforms/Utils/Cloning.h"
 #include <algorithm>
 #include <cstdio>
+#include <utility>
 
 using namespace clang;
 using namespace CodeGen;
@@ -1308,44 +1309,33 @@ void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
 
   CharUnits ComponentWidth = GetTargetTypeStoreSize(getVTableComponentType());
 
-  typedef std::pair<const CXXRecordDecl *, unsigned> AddressPoint;
+  struct AddressPoint {
+    const CXXRecordDecl *Base;
+    size_t Offset;
+    std::string TypeName;
+    bool operator<(const AddressPoint &RHS) const {
+      int D = TypeName.compare(RHS.TypeName);
+      return D < 0 || (D == 0 && Offset < RHS.Offset);
+    }
+  };
   std::vector<AddressPoint> AddressPoints;
-  for (auto &&AP : VTLayout.getAddressPoints())
-    AddressPoints.push_back(std::make_pair(
-        AP.first.getBase(), VTLayout.getVTableOffset(AP.second.VTableIndex) +
-                                AP.second.AddressPointIndex));
-
-  // Sort the address points for determinism.
-  // FIXME: It's more efficient to mangle the types before sorting.
-  llvm::sort(AddressPoints, [this](const AddressPoint &AP1,
-                                   const AddressPoint &AP2) {
-    if (&AP1 == &AP2)
-      return false;
-
-    std::string S1;
-    llvm::raw_string_ostream O1(S1);
-    getCXXABI().getMangleContext().mangleCanonicalTypeName(
-        QualType(AP1.first->getTypeForDecl(), 0), O1);
-    O1.flush();
-
-    std::string S2;
-    llvm::raw_string_ostream O2(S2);
+  for (auto &&AP : VTLayout.getAddressPoints()) {
+    AddressPoint N{AP.first.getBase(),
+                   VTLayout.getVTableOffset(AP.second.VTableIndex) +
+                       AP.second.AddressPointIndex};
+    llvm::raw_string_ostream Stream(N.TypeName);
     getCXXABI().getMangleContext().mangleCanonicalTypeName(
-        QualType(AP2.first->getTypeForDecl(), 0), O2);
-    O2.flush();
-
-    if (S1 < S2)
-      return true;
-    if (S1 != S2)
-      return false;
+        QualType(N.Base->getTypeForDecl(), 0), Stream);
+    AddressPoints.push_back(std::move(N));
+  }
 
-    return AP1.second < AP2.second;
-  });
+  // Sort the address points for determinism.
+  llvm::sort(AddressPoints);
 
   ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();
   for (auto AP : AddressPoints) {
     // Create type metadata for the address point.
-    AddVTableTypeMetadata(VTable, ComponentWidth * AP.second, AP.first);
+    AddVTableTypeMetadata(VTable, ComponentWidth * AP.Offset, AP.Base);
 
     // The class associated with each address point could also potentially be
     // used for indirect calls via a member function pointer, so we need to
@@ -1357,7 +1347,7 @@ void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
       llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(
           Context.getMemberPointerType(
               Comps[I].getFunctionDecl()->getType(),
-              Context.getRecordType(AP.first).getTypePtr()));
+              Context.getRecordType(AP.Base).getTypePtr()));
       VTable->addTypeMetadata((ComponentWidth * I).getQuantity(), MD);
     }
   }