[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336721 91177308-0d34-0410-b5e6-96231b3b80d8

6 files changed, 40 insertions, 16 deletions

diff --git a/include/llvm/Transforms/IPO/FunctionImport.h b/include/llvm/Transforms/IPO/FunctionImport.h
index 5fedde1126b..369a12e5e90 100644
--- a/include/llvm/Transforms/IPO/FunctionImport.h
+++ b/include/llvm/Transforms/IPO/FunctionImport.h
@@ -143,9 +143,9 @@ void gatherImportedSummariesForModule(
     std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex);
 
 /// Emit into \p OutputFilename the files module \p ModulePath will import from.
-std::error_code
-EmitImportsFiles(StringRef ModulePath, StringRef OutputFilename,
-                 const FunctionImporter::ImportMapTy &ModuleImports);
+std::error_code EmitImportsFiles(
+    StringRef ModulePath, StringRef OutputFilename,
+    const std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex);
 
 /// Resolve WeakForLinker values in \p TheModule based on the information
 /// recorded in the summaries during global summary-based analysis.
diff --git a/lib/LTO/LTO.cpp b/lib/LTO/LTO.cpp
index 6077b3b1ba4..34cca32e06e 100644
--- a/lib/LTO/LTO.cpp
+++ b/lib/LTO/LTO.cpp
@@ -1097,7 +1097,8 @@ public:
     WriteIndexToFile(CombinedIndex, OS, &ModuleToSummariesForIndex);
 
     if (ShouldEmitImportsFiles) {
-      EC = EmitImportsFiles(ModulePath, NewModulePath + ".imports", ImportList);
+      EC = EmitImportsFiles(ModulePath, NewModulePath + ".imports",
+                            ModuleToSummariesForIndex);
       if (EC)
         return errorCodeToError(EC);
     }
diff --git a/lib/LTO/ThinLTOCodeGenerator.cpp b/lib/LTO/ThinLTOCodeGenerator.cpp
index d7fac6a993f..90d0f9bdb88 100644
--- a/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/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");
 }
diff --git a/lib/Transforms/IPO/FunctionImport.cpp b/lib/Transforms/IPO/FunctionImport.cpp
index 38f4d981952..c2907937e70 100644
--- a/lib/Transforms/IPO/FunctionImport.cpp
+++ b/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();
 }
 
diff --git a/test/ThinLTO/X86/Inputs/emit_imports2.ll b/test/ThinLTO/X86/Inputs/emit_imports2.ll
new file mode 100644
index 00000000000..2136ec3471d
--- /dev/null
+++ b/test/ThinLTO/X86/Inputs/emit_imports2.ll
@@ -0,0 +1,7 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @h() {
+entry:
+  ret void
+}
diff --git a/test/ThinLTO/X86/emit_imports.ll b/test/ThinLTO/X86/emit_imports.ll
index fc025f416ae..41dc1482cb0 100644
--- a/test/ThinLTO/X86/emit_imports.ll
+++ b/test/ThinLTO/X86/emit_imports.ll
@@ -1,17 +1,19 @@
 ; RUN: opt -module-summary %s -o %t1.bc
 ; RUN: opt -module-summary %p/Inputs/emit_imports.ll -o %t2.bc
+; RUN: opt -module-summary %p/Inputs/emit_imports2.ll -o %t2b.bc
 ; Include a file with an empty module summary index, to ensure that the expected
 ; output files are created regardless, for a distributed build system.
 ; RUN: opt -module-summary %p/Inputs/empty.ll -o %t3.bc
 ; RUN: rm -f %t3.bc.imports
-; RUN: llvm-lto -thinlto-action=thinlink -o %t.index.bc %t1.bc %t2.bc %t3.bc
-; RUN: llvm-lto -thinlto-action=emitimports -thinlto-index %t.index.bc %t1.bc %t2.bc %t3.bc
+; RUN: llvm-lto -thinlto-action=thinlink -o %t.index.bc %t1.bc %t2.bc %t2b.bc %t3.bc
+; RUN: llvm-lto -thinlto-action=emitimports -thinlto-index %t.index.bc %t1.bc %t2.bc %t2b.bc %t3.bc
 
 ; The imports file for this module contains the bitcode file for
 ; Inputs/emit_imports.ll
-; RUN: cat %t1.bc.imports | count 1
+; RUN: cat %t1.bc.imports | count 2
 ; RUN: cat %t1.bc.imports | FileCheck %s --check-prefix=IMPORTS1
 ; IMPORTS1: emit_imports.ll.tmp2.bc
+; IMPORTS1: emit_imports.ll.tmp2b.bc
 
 ; The imports file for Input/emit_imports.ll is empty as it does not import anything.
 ; RUN: cat %t2.bc.imports | count 0
@@ -22,13 +24,15 @@
 ; RUN: rm -f %t1.thinlto.bc %t1.bc.imports
 ; RUN: rm -f %t2.thinlto.bc %t2.bc.imports
 ; RUN: rm -f %t3.bc.thinlto.bc %t3.bc.imports
-; RUN: llvm-lto2 run %t1.bc %t2.bc %t3.bc -o %t.o -save-temps \
+; RUN: llvm-lto2 run %t1.bc %t2.bc %t2b.bc %t3.bc -o %t.o -save-temps \
 ; RUN:     -thinlto-distributed-indexes \
 ; RUN:     -r=%t1.bc,g, \
+; RUN:     -r=%t1.bc,h, \
 ; RUN:     -r=%t1.bc,f,px \
-; RUN:     -r=%t2.bc,g,px
+; RUN:     -r=%t2.bc,g,px \
+; RUN:     -r=%t2b.bc,h,px
 
-; RUN: cat %t1.bc.imports | count 1
+; RUN: cat %t1.bc.imports | count 2
 ; RUN: cat %t1.bc.imports | FileCheck %s --check-prefix=IMPORTS1
 
 ; The imports file for Input/emit_imports.ll is empty as it does not import anything.
@@ -44,9 +48,11 @@ target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 declare void @g(...)
+declare void @h(...)
 
 define void @f() {
 entry:
   call void (...) @g()
+  call void (...) @h()
   ret void
 }