[DTLTO][LLVM] Store the Target Triple for ThinLTO modules.

This will be used for supplying a `-target=<triple>` option to clang for
DTLTO.

Note that If DTLTO is changed to use an optimisation tool that does not
require an explicit triple to be passed then the triple handling can be
removed entirely.

Author: bd1976bris

llvm/include/llvm/LTO/LTO.h

@@ -228,7 +228,8 @@ class ThinBackendProc {
       const FunctionImporter::ImportMapTy &ImportList,
       const FunctionImporter::ExportSetTy &ExportList,
       const std::map<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR,
-      MapVector<StringRef, BitcodeModule> &ModuleMap) = 0;
+      MapVector<StringRef, BitcodeModule> &ModuleMap,
+      DenseMap<StringRef, std::string> &ModuleTriples) = 0;
   Error wait() {
     BackendThreadPool.wait();
     if (Err)
@@ -426,6 +427,7 @@ class LTO {
     // The bitcode modules to compile, if specified by the LTO Config.
     std::optional<ModuleMapType> ModulesToCompile;
     DenseMap<GlobalValue::GUID, StringRef> PrevailingModuleForGUID;
+    DenseMap<StringRef, std::string> ModuleTriples;
   } ThinLTO;
 
   // The global resolution for a particular (mangled) symbol name. This is in
@@ -517,7 +519,8 @@ class LTO {
                        bool LivenessFromIndex);
 
   Error addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
-                   const SymbolResolution *&ResI, const SymbolResolution *ResE);
+                   const SymbolResolution *&ResI, const SymbolResolution *ResE,
+                   StringRef Triple);
 
   Error runRegularLTO(AddStreamFn AddStream);
   Error runThinLTO(AddStreamFn AddStream, FileCache Cache,

llvm/lib/LTO/LTO.cpp

@@ -783,7 +783,7 @@ Error LTO::addModule(InputFile &Input, unsigned ModI,
                        LTOInfo->HasSummary);
 
   if (IsThinLTO)
-    return addThinLTO(BM, ModSyms, ResI, ResE);
+    return addThinLTO(BM, ModSyms, ResI, ResE, Input.getTargetTriple());
 
   RegularLTO.EmptyCombinedModule = false;
   Expected<RegularLTOState::AddedModule> ModOrErr =
@@ -1030,7 +1030,7 @@ Error LTO::linkRegularLTO(RegularLTOState::AddedModule Mod,
 // Add a ThinLTO module to the link.
 Error LTO::addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
                       const SymbolResolution *&ResI,
-                      const SymbolResolution *ResE) {
+                      const SymbolResolution *ResE, StringRef Triple) {
   const SymbolResolution *ResITmp = ResI;
   for (const InputFile::Symbol &Sym : Syms) {
     assert(ResITmp != ResE);
@@ -1090,6 +1090,8 @@ Error LTO::addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
         "Expected at most one ThinLTO module per bitcode file",
         inconvertibleErrorCode());
 
+  ThinLTO.ModuleTriples.insert({BM.getModuleIdentifier(), Triple.str()});
+
   if (!Conf.ThinLTOModulesToCompile.empty()) {
     if (!ThinLTO.ModulesToCompile)
       ThinLTO.ModulesToCompile = ModuleMapType();
@@ -1496,7 +1498,8 @@ class InProcessThinBackend : public ThinBackendProc {
       const FunctionImporter::ImportMapTy &ImportList,
       const FunctionImporter::ExportSetTy &ExportList,
       const std::map<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR,
-      MapVector<StringRef, BitcodeModule> &ModuleMap) override {
+      MapVector<StringRef, BitcodeModule> &ModuleMap,
+      DenseMap<StringRef, std::string> & /*ModuleTriples*/) override {
     StringRef ModulePath = BM.getModuleIdentifier();
     assert(ModuleToDefinedGVSummaries.count(ModulePath));
     const GVSummaryMapTy &DefinedGlobals =
@@ -1776,7 +1779,8 @@ class WriteIndexesThinBackend : public ThinBackendProc {
       const FunctionImporter::ImportMapTy &ImportList,
       const FunctionImporter::ExportSetTy &ExportList,
       const std::map<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR,
-      MapVector<StringRef, BitcodeModule> &ModuleMap) override {
+      MapVector<StringRef, BitcodeModule> &ModuleMap,
+      DenseMap<StringRef, std::string> & /*ModuleTriples*/) override {
     StringRef ModulePath = BM.getModuleIdentifier();
 
     // The contents of this file may be used as input to a native link, and must
@@ -2013,7 +2017,7 @@ Error LTO::runThinLTO(AddStreamFn AddStream, FileCache Cache,
       return BackendProcess->start(
           RegularLTO.ParallelCodeGenParallelismLevel + I, Mod.second,
           ImportLists[Mod.first], ExportLists[Mod.first],
-          ResolvedODR[Mod.first], ThinLTO.ModuleMap);
+          ResolvedODR[Mod.first], ThinLTO.ModuleMap, ThinLTO.ModuleTriples);
     };
 
     if (BackendProcess->getThreadCount() == 1 ||