[LTO][ThinLTO] Use the linker resolutions to mark global values as dso_local.

Now that we have a way to mark GlobalValues as local we can use the symbol
resolutions that the linker plugin provides as part of lto/thinlto link
step to refine the compilers view on what symbols will end up being local.

Differential Revision: https://reviews.llvm.org/D35702

llvm-svn: 317374

1 files changed, 16 insertions, 5 deletions

diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 017dd20..9c73779 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -630,6 +630,9 @@ LTO::addRegularLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
           NonPrevailingComdats.insert(GV->getComdat());
         cast<GlobalObject>(GV)->setComdat(nullptr);
       }
+
+      // Set the 'local' flag based on the linker resolution for this symbol.
+      GV->setDSOLocal(Res.FinalDefinitionInLinkageUnit);
     }
     // Common resolution: collect the maximum size/alignment over all commons.
     // We also record if we see an instance of a common as prevailing, so that
@@ -643,7 +646,6 @@ LTO::addRegularLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
       CommonRes.Prevailing |= Res.Prevailing;
     }
 
-    // FIXME: use proposed local attribute for FinalDefinitionInLinkageUnit.
   }
   if (!M.getComdatSymbolTable().empty())
     for (GlobalValue &GV : M.global_values())
@@ -698,10 +700,10 @@ Error LTO::addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
     assert(ResI != ResE);
     SymbolResolution Res = *ResI++;
 
-    if (Res.Prevailing) {
-      if (!Sym.getIRName().empty()) {
-        auto GUID = GlobalValue::getGUID(GlobalValue::getGlobalIdentifier(
-            Sym.getIRName(), GlobalValue::ExternalLinkage, ""));
+    if (!Sym.getIRName().empty()) {
+      auto GUID = GlobalValue::getGUID(GlobalValue::getGlobalIdentifier(
+          Sym.getIRName(), GlobalValue::ExternalLinkage, ""));
+      if (Res.Prevailing) {
         ThinLTO.PrevailingModuleForGUID[GUID] = BM.getModuleIdentifier();
 
         // For linker redefined symbols (via --wrap or --defsym) we want to
@@ -713,6 +715,15 @@ Error LTO::addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
                   GUID, BM.getModuleIdentifier()))
             S->setLinkage(GlobalValue::WeakAnyLinkage);
       }
+
+      // If the linker resolved the symbol to a local definition then mark it
+      // as local in the summary for the module we are adding.
+      if (Res.FinalDefinitionInLinkageUnit) {
+        if (auto S = ThinLTO.CombinedIndex.findSummaryInModule(
+                GUID, BM.getModuleIdentifier())) {
+          S->setDSOLocal(true);
+        }
+      }
     }
   }