[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, 7 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 31531beea5e..1196dd0099b 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -897,8 +897,8 @@ bool llvm::convertToDeclaration(GlobalValue &GV) {
   return true;
 }
 
-/// Fixup WeakForLinker linkages in \p TheModule based on summary analysis.
-void llvm::thinLTOResolveWeakForLinkerModule(
+/// Fixup prevailing symbol linkages in \p TheModule based on summary analysis.
+void llvm::thinLTOResolvePrevailingInModule(
     Module &TheModule, const GVSummaryMapTy &DefinedGlobals) {
   auto updateLinkage = [&](GlobalValue &GV) {
     // See if the global summary analysis computed a new resolved linkage.
@@ -915,13 +915,15 @@ void llvm::thinLTOResolveWeakForLinkerModule(
     // as we need access to the resolution vectors for each input file in
     // order to find which symbols have been redefined.
     // We may consider reorganizing this code and moving the linkage recording
-    // somewhere else, e.g. in thinLTOResolveWeakForLinkerInIndex.
+    // somewhere else, e.g. in thinLTOResolvePrevailingInIndex.
     if (NewLinkage == GlobalValue::WeakAnyLinkage) {
       GV.setLinkage(NewLinkage);
       return;
     }
 
-    if (!GlobalValue::isWeakForLinker(GV.getLinkage()))
+    if (GlobalValue::isLocalLinkage(GV.getLinkage()) ||
+        // In case it was dead and already converted to declaration.
+        GV.isDeclaration())
       return;
     // Check for a non-prevailing def that has interposable linkage
     // (e.g. non-odr weak or linkonce). In that case we can't simply
@@ -932,7 +934,7 @@ void llvm::thinLTOResolveWeakForLinkerModule(
         GlobalValue::isInterposableLinkage(GV.getLinkage())) {
       if (!convertToDeclaration(GV))
         // FIXME: Change this to collect replaced GVs and later erase
-        // them from the parent module once thinLTOResolveWeakForLinkerGUID is
+        // them from the parent module once thinLTOResolvePrevailingGUID is
         // changed to enable this for aliases.
         llvm_unreachable("Expected GV to be converted");
     } else {