[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, 9 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 38f4d981952..c2907937e70 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -707,15 +707,19 @@ void llvm::gatherImportedSummariesForModule(
 }
 
 /// Emit the files \p ModulePath will import from into \p OutputFilename.
-std::error_code
-llvm::EmitImportsFiles(StringRef ModulePath, StringRef OutputFilename,
-                       const FunctionImporter::ImportMapTy &ModuleImports) {
+std::error_code llvm::EmitImportsFiles(
+    StringRef ModulePath, StringRef OutputFilename,
+    const std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex) {
   std::error_code EC;
   raw_fd_ostream ImportsOS(OutputFilename, EC, sys::fs::OpenFlags::F_None);
   if (EC)
     return EC;
-  for (auto &ILI : ModuleImports)
-    ImportsOS << ILI.first() << "\n";
+  for (auto &ILI : ModuleToSummariesForIndex)
+    // The ModuleToSummariesForIndex map includes an entry for the current
+    // Module (needed for writing out the index files). We don't want to
+    // include it in the imports file, however, so filter it out.
+    if (ILI.first != ModulePath)
+      ImportsOS << ILI.first << "\n";
   return std::error_code();
 }