Use LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN instead of the "dso list".

There are two ways one could implement hiding of linkonce_odr symbols in LTO:
* LLVM tells the linker which symbols can be hidden if not used from native
  files.
* The linker tells LLVM which symbols are not used from other object files,
  but will be put in the dso symbol table if present.

GOLD's API is the second option. It was implemented almost 1:1 in llvm by
passing the list down to internalize.

LLVM already had partial support for the first option. It is also very similar
to how ld64 handles hiding these symbols when *not* doing LTO.

This patch then
* removes the APIs for the DSO list.
* marks LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN all linkonce_odr unnamed_addr
  global values and other linkonce_odr whose address is not used.
* makes the gold plugin responsible for handling the API mismatch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193800 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 28 insertions, 10 deletions

diff --git a/lib/LTO/LTOCodeGenerator.cpp b/lib/LTO/LTOCodeGenerator.cpp
index c55eccb..3c9a378 100644
--- a/lib/LTO/LTOCodeGenerator.cpp
+++ b/lib/LTO/LTOCodeGenerator.cpp
@@ -313,7 +313,6 @@ bool LTOCodeGenerator::determineTarget(std::string &errMsg) {
 void LTOCodeGenerator::
 applyRestriction(GlobalValue &GV,
                  std::vector<const char*> &MustPreserveList,
-                 std::vector<const char*> &DSOList,
                  SmallPtrSet<GlobalValue*, 8> &AsmUsed,
                  Mangler &Mangler) {
   SmallString<64> Buffer;
@@ -323,8 +322,6 @@ applyRestriction(GlobalValue &GV,
     return;
   if (MustPreserveSymbols.count(Buffer))
     MustPreserveList.push_back(GV.getName().data());
-  if (DSOSymbols.count(Buffer))
-    DSOList.push_back(GV.getName().data());
   if (AsmUndefinedRefs.count(Buffer))
     AsmUsed.insert(&GV);
 }
@@ -352,18 +349,17 @@ void LTOCodeGenerator::applyScopeRestrictions() {
   // mark which symbols can not be internalized
   Mangler Mangler(TargetMach);
   std::vector<const char*> MustPreserveList;
-  std::vector<const char*> DSOList;
   SmallPtrSet<GlobalValue*, 8> AsmUsed;
 
   for (Module::iterator f = mergedModule->begin(),
          e = mergedModule->end(); f != e; ++f)
-    applyRestriction(*f, MustPreserveList, DSOList, AsmUsed, Mangler);
+    applyRestriction(*f, MustPreserveList, AsmUsed, Mangler);
   for (Module::global_iterator v = mergedModule->global_begin(),
          e = mergedModule->global_end(); v !=  e; ++v)
-    applyRestriction(*v, MustPreserveList, DSOList, AsmUsed, Mangler);
+    applyRestriction(*v, MustPreserveList, AsmUsed, Mangler);
   for (Module::alias_iterator a = mergedModule->alias_begin(),
          e = mergedModule->alias_end(); a != e; ++a)
-    applyRestriction(*a, MustPreserveList, DSOList, AsmUsed, Mangler);
+    applyRestriction(*a, MustPreserveList, AsmUsed, Mangler);
 
   GlobalVariable *LLVMCompilerUsed =
     mergedModule->getGlobalVariable("llvm.compiler.used");
@@ -391,7 +387,7 @@ void LTOCodeGenerator::applyScopeRestrictions() {
     LLVMCompilerUsed->setSection("llvm.metadata");
   }
 
-  passes.add(createInternalizePass(MustPreserveList, DSOList));
+  passes.add(createInternalizePass(MustPreserveList));
 
   // apply scope restrictions
   passes.run(*mergedModule);
diff --git a/lib/LTO/LTOModule.cpp b/lib/LTO/LTOModule.cpp
index db9b9c9..91240aa 100644
--- a/lib/LTO/LTOModule.cpp
+++ b/lib/LTO/LTOModule.cpp
@@ -38,6 +38,7 @@
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/system_error.h"
 #include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Transforms/Utils/GlobalStatus.h"
 using namespace llvm;
 
 LTOModule::LTOModule(llvm::Module *m, llvm::TargetMachine *t)
@@ -162,6 +163,8 @@ LTOModule *LTOModule::makeLTOModule(MemoryBuffer *buffer,
 
   TargetMachine *target = march->createTargetMachine(TripleStr, CPU, FeatureStr,
                                                      options);
+  m->MaterializeAllPermanently();
+
   LTOModule *Ret = new LTOModule(m.take(), target);
   if (Ret->parseSymbols(errMsg)) {
     delete Ret;
@@ -333,6 +336,25 @@ void LTOModule::addDefinedFunctionSymbol(const Function *f) {
   addDefinedSymbol(f, true);
 }
 
+static bool canBeHidden(const GlobalValue *GV) {
+  GlobalValue::LinkageTypes L = GV->getLinkage();
+
+  if (L == GlobalValue::LinkOnceODRAutoHideLinkage)
+    return true;
+
+  if (L != GlobalValue::LinkOnceODRLinkage)
+    return false;
+
+  if (GV->hasUnnamedAddr())
+    return true;
+
+  GlobalStatus GS;
+  if (GlobalStatus::analyzeGlobal(GV, GS))
+    return false;
+
+  return !GS.IsCompared;
+}
+
 /// addDefinedSymbol - Add a defined symbol to the list.
 void LTOModule::addDefinedSymbol(const GlobalValue *def, bool isFunction) {
   // ignore all llvm.* symbols
@@ -372,12 +394,12 @@ void LTOModule::addDefinedSymbol(const GlobalValue *def, bool isFunction) {
     attr |= LTO_SYMBOL_SCOPE_HIDDEN;
   else if (def->hasProtectedVisibility())
     attr |= LTO_SYMBOL_SCOPE_PROTECTED;
+  else if (canBeHidden(def))
+    attr |= LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN;
   else if (def->hasExternalLinkage() || def->hasWeakLinkage() ||
            def->hasLinkOnceLinkage() || def->hasCommonLinkage() ||
            def->hasLinkerPrivateWeakLinkage())
     attr |= LTO_SYMBOL_SCOPE_DEFAULT;
-  else if (def->hasLinkOnceODRAutoHideLinkage())
-    attr |= LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN;
   else
     attr |= LTO_SYMBOL_SCOPE_INTERNAL;