[llvm] r316045 - [GlobalDCE] Use DenseMap instead of unordered_multimap for GVDependencies.

[Michael Zolotukhin via llvm-commits]

Author: mzolotukhin
Date: Tue Oct 17 16:47:06 2017
New Revision: 316045

URL: http://llvm.org/viewvc/llvm-project?rev=316045&view=rev
Log:
[GlobalDCE] Use DenseMap instead of unordered_multimap for GVDependencies.

Summary:
std::unordered_multimap happens to be very slow when the number of elements
grows large. On one of our internal applications we observed a 17x compile time
improvement from changing it to DenseMap.

Reviewers: mehdi_amini, serge-sans-paille, davide

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D38916

Modified:
    llvm/trunk/include/llvm/Transforms/IPO/GlobalDCE.h
    llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp

Modified: llvm/trunk/include/llvm/Transforms/IPO/GlobalDCE.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/IPO/GlobalDCE.h?rev=316045&r1=316044&r2=316045&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/IPO/GlobalDCE.h (original)
+++ llvm/trunk/include/llvm/Transforms/IPO/GlobalDCE.h Tue Oct 17 16:47:06 2017
@@ -35,7 +35,7 @@ private:
   SmallPtrSet<GlobalValue*, 32> AliveGlobals;
 
   /// Global -> Global that uses this global.
-  std::unordered_multimap<GlobalValue *, GlobalValue *> GVDependencies;
+  DenseMap<GlobalValue *, SmallPtrSet<GlobalValue *, 4>> GVDependencies;
 
   /// Constant -> Globals that use this global cache.
   std::unordered_map<Constant *, SmallPtrSet<GlobalValue *, 8>>

Modified: llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp?rev=316045&r1=316044&r2=316045&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp Tue Oct 17 16:47:06 2017
@@ -115,7 +115,7 @@ void GlobalDCEPass::UpdateGVDependencies
     ComputeDependencies(User, Deps);
   Deps.erase(&GV); // Remove self-reference.
   for (GlobalValue *GVU : Deps) {
-    GVDependencies.insert(std::make_pair(GVU, &GV));
+    GVDependencies[GVU].insert(&GV);
   }
 }
 
@@ -199,8 +199,8 @@ PreservedAnalyses GlobalDCEPass::run(Mod
                                            AliveGlobals.end()};
   while (!NewLiveGVs.empty()) {
     GlobalValue *LGV = NewLiveGVs.pop_back_val();
-    for (auto &&GVD : make_range(GVDependencies.equal_range(LGV)))
-      MarkLive(*GVD.second, &NewLiveGVs);
+    for (auto *GVD : GVDependencies[LGV])
+      MarkLive(*GVD, &NewLiveGVs);
   }
 
   // Now that all globals which are needed are in the AliveGlobals set, we loop