[ThinLTO] Auto-hide prevailing linkonce_odr only when all copies eligible

Summary:
We hit undefined references building with ThinLTO when one source file
contained explicit instantiations of a template method (weak_odr) but
there were also implicit instantiations in another file (linkonce_odr),
and the latter was the prevailing copy. In this case the symbol was
marked hidden when the prevailing linkonce_odr copy was promoted to
weak_odr. It led to unsats when the resulting shared library was linked
with other code that contained a reference (expecting to be resolved due
to the explicit instantiation).

Add a CanAutoHide flag to the GV summary to allow the thin link to
identify when all copies are eligible for auto-hiding (because they were
all originally linkonce_odr global unnamed addr), and only do the
auto-hide in that case.

Most of the changes here are due to plumbing the new flag through the
bitcode and llvm assembly, and resulting test changes. I augmented the
existing auto-hide test to check for this situation.

Reviewers: pcc

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59709

llvm-svn: 360466

1 files changed, 8 insertions, 4 deletions

diff --git a/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp b/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
index 68eb1ef90eb..5282c292263 100644
--- a/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
+++ b/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
@@ -391,7 +391,8 @@ static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
   bool NotEligibleForImport =
       NonRenamableLocal || HasInlineAsmMaybeReferencingInternal;
   GlobalValueSummary::GVFlags Flags(F.getLinkage(), NotEligibleForImport,
-                                    /* Live = */ false, F.isDSOLocal());
+                                    /* Live = */ false, F.isDSOLocal(),
+                                    F.hasLinkOnceODRLinkage() && F.hasGlobalUnnamedAddr());
   FunctionSummary::FFlags FunFlags{
       F.hasFnAttribute(Attribute::ReadNone),
       F.hasFnAttribute(Attribute::ReadOnly),
@@ -418,7 +419,8 @@ computeVariableSummary(ModuleSummaryIndex &Index, const GlobalVariable &V,
   bool HasBlockAddress = findRefEdges(Index, &V, RefEdges, Visited);
   bool NonRenamableLocal = isNonRenamableLocal(V);
   GlobalValueSummary::GVFlags Flags(V.getLinkage(), NonRenamableLocal,
-                                    /* Live = */ false, V.isDSOLocal());
+                                    /* Live = */ false, V.isDSOLocal(),
+                                    V.hasLinkOnceODRLinkage() && V.hasGlobalUnnamedAddr());
 
   // Don't mark variables we won't be able to internalize as read-only.
   GlobalVarSummary::GVarFlags VarFlags(
@@ -438,7 +440,8 @@ computeAliasSummary(ModuleSummaryIndex &Index, const GlobalAlias &A,
                     DenseSet<GlobalValue::GUID> &CantBePromoted) {
   bool NonRenamableLocal = isNonRenamableLocal(A);
   GlobalValueSummary::GVFlags Flags(A.getLinkage(), NonRenamableLocal,
-                                    /* Live = */ false, A.isDSOLocal());
+                                    /* Live = */ false, A.isDSOLocal(),
+                                    A.hasLinkOnceODRLinkage() && A.hasGlobalUnnamedAddr());
   auto AS = llvm::make_unique<AliasSummary>(Flags);
   auto *Aliasee = A.getBaseObject();
   auto AliaseeVI = Index.getValueInfo(Aliasee->getGUID());
@@ -513,7 +516,8 @@ ModuleSummaryIndex llvm::buildModuleSummaryIndex(
           GlobalValueSummary::GVFlags GVFlags(GlobalValue::InternalLinkage,
                                               /* NotEligibleToImport = */ true,
                                               /* Live = */ true,
-                                              /* Local */ GV->isDSOLocal());
+                                              /* Local */ GV->isDSOLocal(),
+                                              GV->hasLinkOnceODRLinkage() && GV->hasGlobalUnnamedAddr());
           CantBePromoted.insert(GV->getGUID());
           // Create the appropriate summary type.
           if (Function *F = dyn_cast<Function>(GV)) {