From d4ee3920c928f51e4c4d70b4fae97f4d99be2583 Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Wed, 24 Apr 2013 17:54:35 +0000
Subject: [PATCH] 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
---
 tools/lto/LTOCodeGenerator.cpp | 38 +++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/tools/lto/LTOCodeGenerator.cpp b/tools/lto/LTOCodeGenerator.cpp
index e7c83f94f53..5f5f76f35fe 100644
--- 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
-- 
2.34.1