[PATCH] D41267: [LTO] Write LTO output for empty RegularLTO.ModsWithSummaries

[Vitaly Buka via Phabricator via llvm-commits]

vitalybuka updated this revision to Diff 127058.
vitalybuka added a comment.

comment


https://reviews.llvm.org/D41267

Files:
  llvm/include/llvm/LTO/LTO.h
  llvm/lib/LTO/LTO.cpp
  llvm/test/ThinLTO/X86/Inputs/distributed_import.ll


Index: llvm/test/ThinLTO/X86/Inputs/distributed_import.ll
===================================================================
--- llvm/test/ThinLTO/X86/Inputs/distributed_import.ll
+++ llvm/test/ThinLTO/X86/Inputs/distributed_import.ll
@@ -1,3 +1,4 @@
+target triple = "x86_64-unknown-linux-gnu"
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 
 @G = internal global i32 7
Index: llvm/lib/LTO/LTO.cpp
===================================================================
--- llvm/lib/LTO/LTO.cpp
+++ llvm/lib/LTO/LTO.cpp
@@ -469,6 +469,9 @@
   if (Conf.ResolutionFile)
     writeToResolutionFile(*Conf.ResolutionFile, Input.get(), Res);
 
+  if (RegularLTO.EmptyModuleTargetTriple.empty())
+    RegularLTO.EmptyModuleTargetTriple = Input->getTargetTriple();
+
   const SymbolResolution *ResI = Res.begin();
   for (unsigned I = 0; I != Input->Mods.size(); ++I)
     if (Error Err = addModule(*Input, I, ResI, Res.end()))
@@ -737,7 +740,9 @@
 
 unsigned LTO::getMaxTasks() const {
   CalledGetMaxTasks = true;
-  return RegularLTO.ParallelCodeGenParallelismLevel + ThinLTO.ModuleMap.size();
+  // Reserve one for empty module.
+  return 1 + RegularLTO.ParallelCodeGenParallelismLevel +
+         ThinLTO.ModuleMap.size();
 }
 
 Error LTO::run(AddStreamFn AddStream, NativeObjectCache Cache) {
@@ -760,9 +765,21 @@
   bool HasRegularLTO = RegularLTO.CombinedModule != nullptr ||
                        !RegularLTO.ModsWithSummaries.empty();
   // Invoke regular LTO if there was a regular LTO module to start with.
-  if (HasRegularLTO)
+  if (HasRegularLTO) {
     if (auto E = runRegularLTO(AddStream))
       return E;
+  } else {
+    // Create empty output to have consistency and avoid workarounds on build
+    // system side for missing build rule output.
+    std::unique_ptr<Module> Mod =
+        make_unique<Module>("empty.o", RegularLTO.Ctx);
+    Mod->setTargetTriple(RegularLTO.EmptyModuleTargetTriple);
+    ModuleSummaryIndex EmptyIndex;
+    if (auto E =
+            backend(Conf, [&](size_t) { return AddStream(getMaxTasks() - 1); },
+                    1, std::move(Mod), EmptyIndex))
+      return E;
+  }
   return runThinLTO(AddStream, Cache, HasRegularLTO);
 }
 
Index: llvm/include/llvm/LTO/LTO.h
===================================================================
--- llvm/include/llvm/LTO/LTO.h
+++ llvm/include/llvm/LTO/LTO.h
@@ -292,6 +292,7 @@
       std::vector<GlobalValue *> Keep;
     };
     std::vector<AddedModule> ModsWithSummaries;
+    std::string EmptyModuleTargetTriple;
   } RegularLTO;
 
   struct ThinLTOState {


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