[PATCH] D52049: [ThinLTOCodeGenerator] Avoid Rehash StringMap in ThreadPool

[Steven Wu via Phabricator via llvm-commits]

steven_wu created this revision.
steven_wu added reviewers: tejohnson, mehdi_amini, kromanova, pcc.
Herald added subscribers: dexonsmith, eraman, inglorion.

During threaded thinLTO, it is possible that the entry for current
module doesn't exist in StringMaps (like ExportLists, ResolvedODR,
etc.). Using operator[] might trigger a rehash for the StringMap, which
might happen on multiple threads at the same time.

rdar://problem/43846199


Repository:
  rL LLVM

https://reviews.llvm.org/D52049

Files:
  lib/LTO/ThinLTOCodeGenerator.cpp


Index: lib/LTO/ThinLTOCodeGenerator.cpp
===================================================================
--- lib/LTO/ThinLTOCodeGenerator.cpp
+++ lib/LTO/ThinLTOCodeGenerator.cpp
@@ -972,6 +972,15 @@
 
   // Parallel optimizer + codegen
   {
+    // Populate the StringMaps to avoid Rehashing in threads.
+    for (auto IndexCount : ModulesOrdering) {
+      auto &ModuleBuffer = Modules[IndexCount];
+      auto ModuleIdentifier = ModuleBuffer.getBufferIdentifier();
+      ExportLists.try_emplace(ModuleIdentifier);
+      ImportLists.try_emplace(ModuleIdentifier);
+      ResolvedODR.try_emplace(ModuleIdentifier);
+      ModuleToDefinedGVSummaries.try_emplace(ModuleIdentifier);
+    }
     ThreadPool Pool(ThreadCount);
     for (auto IndexCount : ModulesOrdering) {
       auto &ModuleBuffer = Modules[IndexCount];


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D52049.165335.patch
Type: text/x-patch
Size: 824 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180913/dbf049d0/attachment.bin>