[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

Change-Id: I25c0597edb56b68b44f49fe2e765893e9643281a
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346436 91177308-0d34-0410-b5e6-96231b3b80d8

11 files changed, 69 insertions, 39 deletions

diff --git a/include/llvm/LTO/LTO.h b/include/llvm/LTO/LTO.h
index 7d6beab6b44..2a3bc9181af 100644
--- a/include/llvm/LTO/LTO.h
+++ b/include/llvm/LTO/LTO.h
@@ -40,13 +40,13 @@ class Module;
 class Target;
 class raw_pwrite_stream;
 
-/// Resolve Weak and LinkOnce values in the \p Index. Linkage changes recorded
-/// in the index and the ThinLTO backends must apply the changes to the Module
-/// via thinLTOResolveWeakForLinkerModule.
+/// Resolve linkage for prevailing symbols in the \p Index. Linkage changes
+/// recorded in the index and the ThinLTO backends must apply the changes to
+/// the module via thinLTOResolvePrevailingInModule.
 ///
 /// This is done for correctness (if value exported, ensure we always
 /// emit a copy), and compile-time optimization (allow drop of duplicates).
-void thinLTOResolveWeakForLinkerInIndex(
+void thinLTOResolvePrevailingInIndex(
     ModuleSummaryIndex &Index,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
         isPrevailing,
diff --git a/include/llvm/Transforms/IPO/FunctionImport.h b/include/llvm/Transforms/IPO/FunctionImport.h
index 5ad880574ef..113ef2e4c7b 100644
--- a/include/llvm/Transforms/IPO/FunctionImport.h
+++ b/include/llvm/Transforms/IPO/FunctionImport.h
@@ -201,10 +201,10 @@ std::error_code EmitImportsFiles(
     StringRef ModulePath, StringRef OutputFilename,
     const std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex);
 
-/// Resolve WeakForLinker values in \p TheModule based on the information
+/// Resolve prevailing symbol linkages in \p TheModule based on the information
 /// recorded in the summaries during global summary-based analysis.
-void thinLTOResolveWeakForLinkerModule(Module &TheModule,
-                                       const GVSummaryMapTy &DefinedGlobals);
+void thinLTOResolvePrevailingInModule(Module &TheModule,
+                                      const GVSummaryMapTy &DefinedGlobals);
 
 /// Internalize \p TheModule based on the information recorded in the summaries
 /// during global summary-based analysis.
diff --git a/lib/LTO/LTO.cpp b/lib/LTO/LTO.cpp
index 2726b6785ed..6b11f690ef3 100644
--- a/lib/LTO/LTO.cpp
+++ b/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,
diff --git a/lib/LTO/LTOBackend.cpp b/lib/LTO/LTOBackend.cpp
index 1f9d60a5bdf..926c419e34a 100644
--- a/lib/LTO/LTOBackend.cpp
+++ b/lib/LTO/LTOBackend.cpp
@@ -490,7 +490,7 @@ Error lto::thinBackend(Config &Conf, unsigned Task, AddStreamFn AddStream,
 
   dropDeadSymbols(Mod, DefinedGlobals, CombinedIndex);
 
-  thinLTOResolveWeakForLinkerModule(Mod, DefinedGlobals);
+  thinLTOResolvePrevailingInModule(Mod, DefinedGlobals);
 
   if (Conf.PostPromoteModuleHook && !Conf.PostPromoteModuleHook(Task, Mod))
     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
diff --git a/lib/LTO/ThinLTOCodeGenerator.cpp b/lib/LTO/ThinLTOCodeGenerator.cpp
index 9500b2ded70..8017527bf22 100644
--- a/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -457,8 +457,8 @@ ProcessThinLTOModule(Module &TheModule, ModuleSummaryIndex &Index,
   if (!SingleModule) {
     promoteModule(TheModule, Index);
 
-    // Apply summary-based LinkOnce/Weak resolution decisions.
-    thinLTOResolveWeakForLinkerModule(TheModule, DefinedGlobals);
+    // Apply summary-based prevailing-symbol resolution decisions.
+    thinLTOResolvePrevailingInModule(TheModule, DefinedGlobals);
 
     // Save temps: after promotion.
     saveTempBitcode(TheModule, SaveTempsDir, count, ".1.promoted.bc");
@@ -500,12 +500,12 @@ ProcessThinLTOModule(Module &TheModule, ModuleSummaryIndex &Index,
   return codegenModule(TheModule, TM);
 }
 
-/// Resolve LinkOnce/Weak symbols. Record resolutions in the \p ResolvedODR map
+/// Resolve prevailing symbols. Record resolutions in the \p ResolvedODR map
 /// for caching, and in the \p Index for application during the ThinLTO
 /// backends. This is needed for correctness for exported symbols (ensure
 /// at least one copy kept) and a compile-time optimization (to drop duplicate
 /// copies when possible).
-static void resolveWeakForLinkerInIndex(
+static void resolvePrevailingInIndex(
     ModuleSummaryIndex &Index,
     StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>>
         &ResolvedODR) {
@@ -527,7 +527,7 @@ static void resolveWeakForLinkerInIndex(
     ResolvedODR[ModuleIdentifier][GUID] = NewLinkage;
   };
 
-  thinLTOResolveWeakForLinkerInIndex(Index, isPrevailing, recordNewLinkage);
+  thinLTOResolvePrevailingInIndex(Index, isPrevailing, recordNewLinkage);
 }
 
 // Initialize the TargetMachine builder for a given Triple
@@ -675,11 +675,11 @@ void ThinLTOCodeGenerator::promote(Module &TheModule,
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
                            ExportLists);
 
-  // Resolve LinkOnce/Weak symbols.
+  // Resolve prevailing symbols
   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;
-  resolveWeakForLinkerInIndex(Index, ResolvedODR);
+  resolvePrevailingInIndex(Index, ResolvedODR);
 
-  thinLTOResolveWeakForLinkerModule(
+  thinLTOResolvePrevailingInModule(
       TheModule, ModuleToDefinedGVSummaries[ModuleIdentifier]);
 
   // Promote the exported values in the index, so that they are promoted
@@ -942,9 +942,9 @@ void ThinLTOCodeGenerator::run() {
   // on the index, and nuke this map.
   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;
 
-  // Resolve LinkOnce/Weak symbols, this has to be computed early because it
+  // Resolve prevailing symbols, this has to be computed early because it
   // impacts the caching.
-  resolveWeakForLinkerInIndex(*Index, ResolvedODR);
+  resolvePrevailingInIndex(*Index, ResolvedODR);
 
   // Use global summary-based analysis to identify symbols that can be
   // internalized (because they aren't exported or preserved as per callback).
diff --git a/lib/Transforms/IPO/FunctionImport.cpp b/lib/Transforms/IPO/FunctionImport.cpp
index 31531beea5e..1196dd0099b 100644
--- a/lib/Transforms/IPO/FunctionImport.cpp
+++ b/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 {
diff --git a/test/LTO/Resolution/X86/dead-strip-fulllto.ll b/test/LTO/Resolution/X86/dead-strip-fulllto.ll
index 773b4385378..11a8981aceb 100644
--- a/test/LTO/Resolution/X86/dead-strip-fulllto.ll
+++ b/test/LTO/Resolution/X86/dead-strip-fulllto.ll
@@ -1,14 +1,14 @@
 ; RUN: opt -module-summary -o %t %s
 ; RUN: opt -module-summary -o %t2 %S/Inputs/dead-strip-fulllto.ll
 
-; RUN: llvm-lto2 run %t -r %t,main,px -r %t,live1,p -r %t,live2,p -r %t,dead2,p \
-; RUN:               %t2 -r %t2,live1, -r %t2,live2, -r %t2,dead1,p -r %t2,dead2, -r %t2,odr, \
+; RUN: llvm-lto2 run %t -r %t,main,px -r %t,live1, -r %t,live2,p -r %t,dead2,p \
+; RUN:               %t2 -r %t2,live1,p -r %t2,live2, -r %t2,dead1,p -r %t2,dead2, -r %t2,odr, \
 ; RUN: -save-temps -o %t3
 ; RUN: llvm-nm %t3.0 | FileCheck --check-prefix=FULL %s
 ; RUN: llvm-nm %t3.1 | FileCheck --check-prefix=THIN %s
 
-; RUN: llvm-lto2 run %t -r %t,main,px -r %t,live1,p -r %t,live2,p -r %t,dead2,p \
-; RUN:               %t2 -r %t2,live1, -r %t2,live2, -r %t2,dead1,p -r %t2,dead2, -r %t2,odr, \
+; RUN: llvm-lto2 run %t -r %t,main,px -r %t,live1, -r %t,live2,p -r %t,dead2,p \
+; RUN:               %t2 -r %t2,live1,p -r %t2,live2, -r %t2,dead1,p -r %t2,dead2, -r %t2,odr, \
 ; RUN: -save-temps -o %t3 -O0
 ; RUN: llvm-nm %t3.0 | FileCheck --check-prefix=FULL %s
 ; RUN: llvm-nm %t3.1 | FileCheck --check-prefix=THIN %s
diff --git a/test/ThinLTO/X86/Inputs/strong_non_prevailing.ll b/test/ThinLTO/X86/Inputs/strong_non_prevailing.ll
new file mode 100644
index 00000000000..5473f817f13
--- /dev/null
+++ b/test/ThinLTO/X86/Inputs/strong_non_prevailing.ll
@@ -0,0 +1,6 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+$__llvm_profile_filename = comdat any
+
+@__llvm_profile_filename = constant [19 x i8] c"default_%m.profraw\00", comdat
diff --git a/test/ThinLTO/X86/funcimport.ll b/test/ThinLTO/X86/funcimport.ll
index 1e8784d7cac..fa1bdbf9f11 100644
--- a/test/ThinLTO/X86/funcimport.ll
+++ b/test/ThinLTO/X86/funcimport.ll
@@ -40,7 +40,7 @@
 ; CODEGEN: T _main
 
 ; Verify that all run together
-; RUN: llvm-lto -thinlto-action=run %t2.bc  %t.bc
+; RUN: llvm-lto -thinlto-action=run %t2.bc  %t.bc  -exported-symbol=_main
 ; RUN: llvm-nm -o - < %t.bc.thinlto.o | FileCheck %s --check-prefix=ALL
 ; RUN: llvm-nm -o - < %t2.bc.thinlto.o | FileCheck %s --check-prefix=ALL2
 ; ALL: T _callfuncptr
diff --git a/test/ThinLTO/X86/strong_non_prevailing.ll b/test/ThinLTO/X86/strong_non_prevailing.ll
new file mode 100644
index 00000000000..f96e23adc3d
--- /dev/null
+++ b/test/ThinLTO/X86/strong_non_prevailing.ll
@@ -0,0 +1,16 @@
+; RUN: opt -module-summary %s -o %t.bc
+; RUN: opt -module-summary %p/Inputs/strong_non_prevailing.ll -o %t2.bc
+
+; RUN: llvm-lto -thinlto-action=run %t.bc %t2.bc -exported-symbol=__llvm_profile_filename
+; RUN: llvm-nm -o - < %t.bc.thinlto.o | FileCheck %s --check-prefix=EXPORTED
+; RUN: llvm-nm -o - < %t2.bc.thinlto.o 2>&1 | FileCheck %s --check-prefix=NOT_EXPORTED
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+$__llvm_profile_filename = comdat any
+
+@__llvm_profile_filename = constant [19 x i8] c"default_%m.profraw\00", comdat
+
+; EXPORTED: N __llvm_profile_filename
+; NOT_EXPORTED-NOT: N __llvm_profile_filename
diff --git a/test/Transforms/FunctionImport/funcimport_var.ll b/test/Transforms/FunctionImport/funcimport_var.ll
index a93cabba69a..edd874e6297 100644
--- a/test/Transforms/FunctionImport/funcimport_var.ll
+++ b/test/Transforms/FunctionImport/funcimport_var.ll
@@ -4,7 +4,7 @@
 ; RUN: opt -module-summary %p/Inputs/funcimport_var2.ll -o %t2.bc
 ; RUN: llvm-lto -thinlto -thinlto-action=thinlink -o %t3 %t.bc %t2.bc
 ; RUN: llvm-lto -thinlto -thinlto-action=import -thinlto-index=%t3 %t.bc %t2.bc
-; RUN: llvm-lto -thinlto -thinlto-action=run %t.bc %t2.bc
+; RUN: llvm-lto -thinlto -thinlto-action=run %t.bc %t2.bc -exported-symbol=_Z4LinkPKcS0_
 ; RUN: llvm-nm %t.bc.thinlto.o | FileCheck %s
 ; RUN: llvm-lto2 run %t.bc %t2.bc -o %t.out \
 ; RUN:   -r %t.bc,_Z4LinkPKcS0_,plx \