[llvm] [ThinLTO] optimize propagateAttributes performance (PR #132917)

[Zhaoxuan Jiang via llvm-commits]

https://github.com/nocchijiang created https://github.com/llvm/llvm-project/pull/132917

ModuleSummaryIndex::propagateAttributes() was observed to take about 25 minutes to complete on a ThinLTO project. Profiling revealed that the majority of this time was spent operating on the MarkedNonReadWriteOnly set.

By moving the storage to a per-GlobalValueSummaryInfo basis, the execution time is dramatically reduced to less than 10 seconds.

>From 44fa6fd075ebd0195427ca612ad69e38d3364f12 Mon Sep 17 00:00:00 2001
From: Zhaoxuan Jiang <jiangzhaoxuan94 at gmail.com>
Date: Tue, 25 Mar 2025 16:52:49 +0800
Subject: [PATCH] [ThinLTO] optimize propagateAttributes performance

ModuleSummaryIndex::propagateAttributes() was observed to take about 25
minutes to complete on a ThinLTO project. Profiling revealed that the
majority of this time was spent operating on the MarkedNonReadWriteOnly
set.

By moving the storage to a per-GlobalValueSummaryInfo basis, the
execution time is dramatically reduced to less than 10 seconds.
---
 llvm/include/llvm/IR/ModuleSummaryIndex.h |  2 ++
 llvm/lib/IR/ModuleSummaryIndex.cpp        | 12 +++++-------
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/llvm/include/llvm/IR/ModuleSummaryIndex.h b/llvm/include/llvm/IR/ModuleSummaryIndex.h
index 2650456c49841..5b59bf23f0dad 100644
--- a/llvm/include/llvm/IR/ModuleSummaryIndex.h
+++ b/llvm/include/llvm/IR/ModuleSummaryIndex.h
@@ -165,6 +165,8 @@ struct alignas(8) GlobalValueSummaryInfo {
   /// in the GlobalValueMap. Requires a vector in the case of multiple
   /// COMDAT values of the same name.
   GlobalValueSummaryList SummaryList;
+
+  mutable bool MarkedNonReadWriteOnly = false;
 };
 
 /// Map from global value GUID to corresponding summary structures. Use a
diff --git a/llvm/lib/IR/ModuleSummaryIndex.cpp b/llvm/lib/IR/ModuleSummaryIndex.cpp
index d9024b0a8673f..7206c12576855 100644
--- a/llvm/lib/IR/ModuleSummaryIndex.cpp
+++ b/llvm/lib/IR/ModuleSummaryIndex.cpp
@@ -199,9 +199,7 @@ bool ModuleSummaryIndex::isGUIDLive(GlobalValue::GUID GUID) const {
   return false;
 }
 
-static void
-propagateAttributesToRefs(GlobalValueSummary *S,
-                          DenseSet<ValueInfo> &MarkedNonReadWriteOnly) {
+static void propagateAttributesToRefs(GlobalValueSummary *S) {
   // If reference is not readonly or writeonly then referenced summary is not
   // read/writeonly either. Note that:
   // - All references from GlobalVarSummary are conservatively considered as
@@ -213,9 +211,10 @@ propagateAttributesToRefs(GlobalValueSummary *S,
   for (auto &VI : S->refs()) {
     assert(VI.getAccessSpecifier() == 0 || isa<FunctionSummary>(S));
     if (!VI.getAccessSpecifier()) {
-      if (!MarkedNonReadWriteOnly.insert(VI).second)
+      if (VI.getRef()->second.MarkedNonReadWriteOnly)
         continue;
-    } else if (MarkedNonReadWriteOnly.contains(VI))
+      VI.getRef()->second.MarkedNonReadWriteOnly = true;
+    } else if (VI.getRef()->second.MarkedNonReadWriteOnly)
       continue;
     for (auto &Ref : VI.getSummaryList())
       // If references to alias is not read/writeonly then aliasee
@@ -260,7 +259,6 @@ void ModuleSummaryIndex::propagateAttributes(
     const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
   if (!PropagateAttrs)
     return;
-  DenseSet<ValueInfo> MarkedNonReadWriteOnly;
   for (auto &P : *this) {
     bool IsDSOLocal = true;
     for (auto &S : P.second.SummaryList) {
@@ -299,7 +297,7 @@ void ModuleSummaryIndex::propagateAttributes(
           GVS->setReadOnly(false);
           GVS->setWriteOnly(false);
         }
-      propagateAttributesToRefs(S.get(), MarkedNonReadWriteOnly);
+      propagateAttributesToRefs(S.get());
 
       // If the flag from any summary is false, the GV is not DSOLocal.
       IsDSOLocal &= S->isDSOLocal();