LTO: Do summary-based prevailing symbol resolution at --lto-O0.

Prevailing symbol resolution is necessary for correctness. Without
this we can end up dropping a referenced linkonce symbol from the link.

Differential Revision: https://reviews.llvm.org/D33570

llvm-svn: 303939

2 files changed, 23 insertions, 13 deletions

diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index c69f3855a19..780f3b713ff 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -1002,10 +1002,6 @@ Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache,
         ExportedGUIDs.insert(GUID);
     }
 
-    auto isPrevailing = [&](GlobalValue::GUID GUID,
-                            const GlobalValueSummary *S) {
-      return ThinLTO.PrevailingModuleForGUID[GUID] == S->modulePath();
-    };
     auto isExported = [&](StringRef ModuleIdentifier, GlobalValue::GUID GUID) {
       const auto &ExportList = ExportLists.find(ModuleIdentifier);
       return (ExportList != ExportLists.end() &&
@@ -1013,17 +1009,20 @@ Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache,
              ExportedGUIDs.count(GUID);
     };
     thinLTOInternalizeAndPromoteInIndex(ThinLTO.CombinedIndex, isExported);
-
-    auto recordNewLinkage = [&](StringRef ModuleIdentifier,
-                                GlobalValue::GUID GUID,
-                                GlobalValue::LinkageTypes NewLinkage) {
-      ResolvedODR[ModuleIdentifier][GUID] = NewLinkage;
-    };
-
-    thinLTOResolveWeakForLinkerInIndex(ThinLTO.CombinedIndex, isPrevailing,
-                                       recordNewLinkage);
   }
 
+  auto isPrevailing = [&](GlobalValue::GUID GUID,
+                          const GlobalValueSummary *S) {
+    return ThinLTO.PrevailingModuleForGUID[GUID] == S->modulePath();
+  };
+  auto recordNewLinkage = [&](StringRef ModuleIdentifier,
+                              GlobalValue::GUID GUID,
+                              GlobalValue::LinkageTypes NewLinkage) {
+    ResolvedODR[ModuleIdentifier][GUID] = NewLinkage;
+  };
+  thinLTOResolveWeakForLinkerInIndex(ThinLTO.CombinedIndex, isPrevailing,
+                                     recordNewLinkage);
+
   std::unique_ptr<ThinBackendProc> BackendProc =
       ThinLTO.Backend(Conf, ThinLTO.CombinedIndex, ModuleToDefinedGVSummaries,
                       AddStream, Cache);
diff --git a/llvm/test/LTO/Resolution/X86/linkonce.ll b/llvm/test/LTO/Resolution/X86/linkonce.ll
new file mode 100644
index 00000000000..33d2df740a4
--- /dev/null
+++ b/llvm/test/LTO/Resolution/X86/linkonce.ll
@@ -0,0 +1,11 @@
+; RUN: opt -module-summary -o %t %s
+; RUN: llvm-lto2 run %t -O0 -r %t,foo,px -o %t2
+; RUN: llvm-nm %t2.0 | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: W foo
+define linkonce_odr void @foo() {
+  ret void
+}