[LTO] Drop non-prevailing definitions only if linkage is not local or appending

Summary:
This fixes PR 37422

In ELF, non-weak symbols can also be non-prevailing.  In this particular
PR, the __llvm_profile_* symbols are non-prevailing but weren't getting
dropped - causing multiply-defined errors with lld.

Also add a test, strong_non_prevailing.ll, to ensure that multiple
copies of a strong symbol are dropped.

To fix the test regressions exposed by this fix,
- do not mark prevailing copies for symbols with 'appending' linkage.
There's no one prevailing copy for such symbols.
- fix the prevailing version in dead-strip-fulllto.ll
- explicitly pass exported symbols to llvm-lto in fumcimport.ll and
funcimport_var.ll

Reviewers: tejohnson, pcc

Subscribers: mehdi_amini, inglorion, eraman, steven_wu, dexonsmith,
dang, srhines, llvm-commits

Differential Revision: https://reviews.llvm.org/D54125

llvm-svn: 346436

1 files changed, 16 insertions, 10 deletions

diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 2726b67..6b11f69 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -282,7 +282,7 @@ static void computeCacheKey(
   Key = toHex(Hasher.result());
 }
 
-static void thinLTOResolveWeakForLinkerGUID(
+static void thinLTOResolvePrevailingGUID(
     GlobalValueSummaryList &GVSummaryList, GlobalValue::GUID GUID,
     DenseSet<GlobalValueSummary *> &GlobalInvolvedWithAlias,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
@@ -291,7 +291,10 @@ static void thinLTOResolveWeakForLinkerGUID(
         recordNewLinkage) {
   for (auto &S : GVSummaryList) {
     GlobalValue::LinkageTypes OriginalLinkage = S->linkage();
-    if (!GlobalValue::isWeakForLinker(OriginalLinkage))
+    // Ignore local and appending linkage values since the linker
+    // doesn't resolve them.
+    if (GlobalValue::isLocalLinkage(OriginalLinkage) ||
+        GlobalValue::isAppendingLinkage(S->linkage()))
       continue;
     // We need to emit only one of these. The prevailing module will keep it,
     // but turned into a weak, while the others will drop it when possible.
@@ -315,13 +318,13 @@ static void thinLTOResolveWeakForLinkerGUID(
   }
 }
 
-// Resolve Weak and LinkOnce values in the \p Index.
+/// Resolve linkage for prevailing symbols in the \p Index.
 //
 // We'd like to drop these functions if they are no longer referenced in the
 // current module. However there is a chance that another module is still
 // referencing them because of the import. We make sure we always emit at least
 // one copy.
-void llvm::thinLTOResolveWeakForLinkerInIndex(
+void llvm::thinLTOResolvePrevailingInIndex(
     ModuleSummaryIndex &Index,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
         isPrevailing,
@@ -337,9 +340,9 @@ void llvm::thinLTOResolveWeakForLinkerInIndex(
         GlobalInvolvedWithAlias.insert(&AS->getAliasee());
 
   for (auto &I : Index)
-    thinLTOResolveWeakForLinkerGUID(I.second.SummaryList, I.first,
-                                    GlobalInvolvedWithAlias, isPrevailing,
-                                    recordNewLinkage);
+    thinLTOResolvePrevailingGUID(I.second.SummaryList, I.first,
+                                 GlobalInvolvedWithAlias, isPrevailing,
+                                 recordNewLinkage);
 }
 
 static void thinLTOInternalizeAndPromoteGUID(
@@ -350,7 +353,10 @@ static void thinLTOInternalizeAndPromoteGUID(
       if (GlobalValue::isLocalLinkage(S->linkage()))
         S->setLinkage(GlobalValue::ExternalLinkage);
     } else if (EnableLTOInternalization &&
-               !GlobalValue::isLocalLinkage(S->linkage()))
+               // Ignore local and appending linkage values since the linker
+               // doesn't resolve them.
+               !GlobalValue::isLocalLinkage(S->linkage()) &&
+               !GlobalValue::isAppendingLinkage(S->linkage()))
       S->setLinkage(GlobalValue::InternalLinkage);
   }
 }
@@ -1205,8 +1211,8 @@ Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache) {
                               GlobalValue::LinkageTypes NewLinkage) {
     ResolvedODR[ModuleIdentifier][GUID] = NewLinkage;
   };
-  thinLTOResolveWeakForLinkerInIndex(ThinLTO.CombinedIndex, isPrevailing,
-                                     recordNewLinkage);
+  thinLTOResolvePrevailingInIndex(ThinLTO.CombinedIndex, isPrevailing,
+                                  recordNewLinkage);
 
   std::unique_ptr<ThinBackendProc> BackendProc =
       ThinLTO.Backend(Conf, ThinLTO.CombinedIndex, ModuleToDefinedGVSummaries,