Don't produce an empty llvm.compiler.used in LTO.

LTO was always creating an empty llvm.compiler.used. With this patch we
now first check if there is anything to be added first.

Unfortunately, there is no good way to test libLTO in isolation as it needs gold
or ld64, but there are bots doing LTO builds that found this problem.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180202 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/tools/lto/LTOCodeGenerator.cpp b/tools/lto/LTOCodeGenerator.cpp
index e7c83f94f5366bf6a06a5840cbb92c47cff7f51f..5f5f76f35fe89864af35570b57b784eac2781e17 100644 (file)
--- a/tools/lto/LTOCodeGenerator.cpp
+++ b/tools/lto/LTOCodeGenerator.cpp
@@ -287,9 +287,7 @@ static void findUsedValues(GlobalVariable *LLVMUsed,
                            SmallPtrSet<GlobalValue*, 8> &UsedValues) {
   if (LLVMUsed == 0) return;
 
-  ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
-  if (Inits == 0) return;
-
+  ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
   for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
     if (GlobalValue *GV =
         dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
@@ -326,24 +324,26 @@ void LTOCodeGenerator::applyScopeRestrictions() {
   if (LLVMCompilerUsed)
     LLVMCompilerUsed->eraseFromParent();
 
-  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);
+  if (!asmUsed.empty()) {
+    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");
   }
 
-  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