[ThinLTO] Use std::map to get determistic imports files

Summary:
I noticed that the .imports files emitted for distributed ThinLTO
backends do not have consistent ordering. This is because StringMap
iteration order is not guaranteed to be deterministic. Since we already
have a std::map with this information, used when emitting the individual
index files (ModuleToSummariesForIndex), use it for the imports files as
well.

This issue is likely causing some unnecessary rebuilds of the ThinLTO
backends in our distributed build system as the imports files are inputs
to those backends.

Reviewers: pcc, steven_wu, mehdi_amini

Subscribers: mehdi_amini, inglorion, eraman, steven_wu, dexonsmith, llvm-commits

Differential Revision: https://reviews.llvm.org/D48783

llvm-svn: 336721

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index d7fac6a993f..90d0f9bdb88 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -758,8 +758,14 @@ void ThinLTOCodeGenerator::emitImports(StringRef ModulePath,
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
                            ExportLists);
 
+  std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
+  llvm::gatherImportedSummariesForModule(ModulePath, ModuleToDefinedGVSummaries,
+                                         ImportLists[ModulePath],
+                                         ModuleToSummariesForIndex);
+
   std::error_code EC;
-  if ((EC = EmitImportsFiles(ModulePath, OutputName, ImportLists[ModulePath])))
+  if ((EC =
+           EmitImportsFiles(ModulePath, OutputName, ModuleToSummariesForIndex)))
     report_fatal_error(Twine("Failed to open ") + OutputName +
                        " to save imports lists\n");
 }