Add a special streamer to libLTO that just records symbols definitions and

uses.

The result produced by the streamer is used to give the linker more accurate
information and to add to llvm.compiler.used. The second improvement removes
the need for the user to add __attribute__((used)) to functions only used in
inline asm. The first one lets us build firefox with LTO on Darwin :-)

llvm-svn: 126830

1 files changed, 75 insertions, 33 deletions

diff --git a/llvm/tools/lto/LTOCodeGenerator.cpp b/llvm/tools/lto/LTOCodeGenerator.cpp
index f72fdb0fca9..6739e067674 100644
--- a/llvm/tools/lto/LTOCodeGenerator.cpp
+++ b/llvm/tools/lto/LTOCodeGenerator.cpp
@@ -75,7 +75,6 @@ LTOCodeGenerator::LTOCodeGenerator()
 {
     InitializeAllTargets();
     InitializeAllAsmPrinters();
-    InitializeAllAsmParsers();
 }
 
 LTOCodeGenerator::~LTOCodeGenerator()
@@ -88,7 +87,13 @@ LTOCodeGenerator::~LTOCodeGenerator()
 
 bool LTOCodeGenerator::addModule(LTOModule* mod, std::string& errMsg)
 {
-    return _linker.LinkInModule(mod->getLLVVMModule(), &errMsg);
+  bool ret = _linker.LinkInModule(mod->getLLVVMModule(), &errMsg);
+
+  const std::vector<const char*> &undefs = mod->getAsmUndefinedRefs();
+  for (int i = 0, e = undefs.size(); i != e; ++i)
+    _asmUndefinedRefs[undefs[i]] = 1;
+
+  return ret;
 }
     
 
@@ -249,6 +254,34 @@ bool LTOCodeGenerator::determineTarget(std::string& errMsg)
     return false;
 }
 
+void LTOCodeGenerator::applyRestriction(GlobalValue &GV,
+                                     std::vector<const char*> &mustPreserveList,
+                                        SmallPtrSet<GlobalValue*, 8> &asmUsed,
+                                        Mangler &mangler) {
+  SmallString<64> Buffer;
+  mangler.getNameWithPrefix(Buffer, &GV, false);
+
+  if (GV.isDeclaration())
+    return;
+  if (_mustPreserveSymbols.count(Buffer))
+    mustPreserveList.push_back(GV.getName().data());
+  if (_asmUndefinedRefs.count(Buffer))
+    asmUsed.insert(&GV);
+}
+
+static void findUsedValues(GlobalVariable *LLVMUsed,
+                           SmallPtrSet<GlobalValue*, 8> &UsedValues) {
+  if (LLVMUsed == 0) return;
+
+  ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
+  if (Inits == 0) return;
+
+  for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
+    if (GlobalValue *GV = 
+          dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
+      UsedValues.insert(GV);
+}
+
 void LTOCodeGenerator::applyScopeRestrictions() {
   if (_scopeRestrictionsDone) return;
   Module *mergedModule = _linker.getModule();
@@ -258,38 +291,47 @@ void LTOCodeGenerator::applyScopeRestrictions() {
   passes.add(createVerifierPass());
 
   // mark which symbols can not be internalized 
-  if (!_mustPreserveSymbols.empty()) {
-    MCContext Context(*_target->getMCAsmInfo(), NULL);
-    Mangler mangler(Context, *_target->getTargetData());
-    std::vector<const char*> mustPreserveList;
-    SmallString<64> Buffer;
-    for (Module::iterator f = mergedModule->begin(),
-         e = mergedModule->end(); f != e; ++f) {
-      Buffer.clear();
-      mangler.getNameWithPrefix(Buffer, f, false);
-      if (!f->isDeclaration() &&
-          _mustPreserveSymbols.count(Buffer))
-        mustPreserveList.push_back(f->getName().data());
-    }
-    for (Module::global_iterator v = mergedModule->global_begin(), 
-         e = mergedModule->global_end(); v !=  e; ++v) {
-      Buffer.clear();
-      mangler.getNameWithPrefix(Buffer, v, false);
-      if (!v->isDeclaration() &&
-          _mustPreserveSymbols.count(Buffer))
-        mustPreserveList.push_back(v->getName().data());
-    }
-    for (Module::alias_iterator a = mergedModule->alias_begin(),
-         e = mergedModule->alias_end(); a != e; ++a) {
-      Buffer.clear();
-      mangler.getNameWithPrefix(Buffer, a, false);
-      if (!a->isDeclaration() &&
-          _mustPreserveSymbols.count(Buffer))
-        mustPreserveList.push_back(a->getName().data());
-    }
-    passes.add(createInternalizePass(mustPreserveList));
+  MCContext Context(*_target->getMCAsmInfo(), NULL);
+  Mangler mangler(Context, *_target->getTargetData());
+  std::vector<const char*> mustPreserveList;
+  SmallPtrSet<GlobalValue*, 8> asmUsed;
+
+  for (Module::iterator f = mergedModule->begin(),
+         e = mergedModule->end(); f != e; ++f)
+    applyRestriction(*f, mustPreserveList, asmUsed, mangler);
+  for (Module::global_iterator v = mergedModule->global_begin(), 
+         e = mergedModule->global_end(); v !=  e; ++v)
+    applyRestriction(*v, mustPreserveList, asmUsed, mangler);
+  for (Module::alias_iterator a = mergedModule->alias_begin(),
+         e = mergedModule->alias_end(); a != e; ++a)
+    applyRestriction(*a, mustPreserveList, asmUsed, mangler);
+
+  GlobalVariable *LLVMCompilerUsed =
+    mergedModule->getGlobalVariable("llvm.compiler.used");
+  findUsedValues(LLVMCompilerUsed, asmUsed);
+  if (LLVMCompilerUsed)
+    LLVMCompilerUsed->eraseFromParent();
+
+  const llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(_context);
+  std::vector<Constant*> asmUsed2;
+  for (SmallPtrSet<GlobalValue*, 16>::const_iterator i = asmUsed.begin(),
+         e = asmUsed.end(); i !=e; ++i) {
+    GlobalValue *GV = *i;
+    Constant *c = ConstantExpr::getBitCast(GV, i8PTy);
+    asmUsed2.push_back(c);
   }
-  
+
+  llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, asmUsed2.size());
+  LLVMCompilerUsed =
+    new llvm::GlobalVariable(*mergedModule, ATy, false,
+                             llvm::GlobalValue::AppendingLinkage,
+                             llvm::ConstantArray::get(ATy, asmUsed2),
+                             "llvm.compiler.used");
+
+  LLVMCompilerUsed->setSection("llvm.metadata");
+
+  passes.add(createInternalizePass(mustPreserveList));
+
   // apply scope restrictions
   passes.run(*mergedModule);