[IR] Disallow llvm.global_ctors and llvm.global_dtors of the 2-field form in textual format

The 3-field form was introduced by D3499 in 2014 and the legacy 2-field
form was planned to be removed in LLVM 4.0

For the textual format, this patch migrates the existing 2-field form to
use the 3-field form and deletes the compatibility code.
test/Verifier/global-ctors-2.ll checks we have a friendly error message.

For bitcode, lib/IR/AutoUpgrade UpgradeGlobalVariables will upgrade the
2-field form (add i8* null as the third field).

Reviewed By: rnk, dexonsmith

Differential Revision: https://reviews.llvm.org/D61547

llvm-svn: 360742

2 files changed, 36 insertions, 10 deletions

diff --git a/llvm/lib/IR/AutoUpgrade.cpp b/llvm/lib/IR/AutoUpgrade.cpp
index c0fd3cd7cbd..e6a096a8855 100644
--- a/llvm/lib/IR/AutoUpgrade.cpp
+++ b/llvm/lib/IR/AutoUpgrade.cpp
@@ -805,9 +805,35 @@ bool llvm::UpgradeIntrinsicFunction(Function *F, Function *&NewFn) {
   return Upgraded;
 }
 
-bool llvm::UpgradeGlobalVariable(GlobalVariable *GV) {
-  // Nothing to do yet.
-  return false;
+GlobalVariable *llvm::UpgradeGlobalVariable(GlobalVariable *GV) {
+  if (!(GV->hasName() && (GV->getName() == "llvm.global_ctors" ||
+                          GV->getName() == "llvm.global_dtors")) ||
+      !GV->hasInitializer())
+    return nullptr;
+  ArrayType *ATy = dyn_cast<ArrayType>(GV->getValueType());
+  if (!ATy)
+    return nullptr;
+  StructType *STy = dyn_cast<StructType>(ATy->getElementType());
+  if (!STy || STy->getNumElements() != 2)
+    return nullptr;
+
+  LLVMContext &C = GV->getContext();
+  IRBuilder<> IRB(C);
+  auto EltTy = StructType::get(STy->getElementType(0), STy->getElementType(1),
+                               IRB.getInt8PtrTy());
+  Constant *Init = GV->getInitializer();
+  unsigned N = Init->getNumOperands();
+  std::vector<Constant *> NewCtors(N);
+  for (unsigned i = 0; i != N; ++i) {
+    auto Ctor = cast<Constant>(Init->getOperand(i));
+    NewCtors[i] = ConstantStruct::get(
+        EltTy, Ctor->getAggregateElement(0u), Ctor->getAggregateElement(1),
+        Constant::getNullValue(IRB.getInt8PtrTy()));
+  }
+  Constant *NewInit = ConstantArray::get(ArrayType::get(EltTy, N), NewCtors);
+
+  return new GlobalVariable(NewInit->getType(), false, GV->getLinkage(),
+                            NewInit, GV->getName());
 }
 
 // Handles upgrading SSE2/AVX2/AVX512BW PSLLDQ intrinsics by converting them
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 1ba64f33380..f7004cf4eae 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -641,18 +641,18 @@ void Verifier::visitGlobalVariable(const GlobalVariable &GV) {
       PointerType *FuncPtrTy =
           FunctionType::get(Type::getVoidTy(Context), false)->
           getPointerTo(DL.getProgramAddressSpace());
-      // FIXME: Reject the 2-field form in LLVM 4.0.
       Assert(STy &&
                  (STy->getNumElements() == 2 || STy->getNumElements() == 3) &&
                  STy->getTypeAtIndex(0u)->isIntegerTy(32) &&
                  STy->getTypeAtIndex(1) == FuncPtrTy,
              "wrong type for intrinsic global variable", &GV);
-      if (STy->getNumElements() == 3) {
-        Type *ETy = STy->getTypeAtIndex(2);
-        Assert(ETy->isPointerTy() &&
-                   cast<PointerType>(ETy)->getElementType()->isIntegerTy(8),
-               "wrong type for intrinsic global variable", &GV);
-      }
+      Assert(STy->getNumElements() == 3,
+             "the third field of the element type is mandatory, "
+             "specify i8* null to migrate from the obsoleted 2-field form");
+      Type *ETy = STy->getTypeAtIndex(2);
+      Assert(ETy->isPointerTy() &&
+                 cast<PointerType>(ETy)->getElementType()->isIntegerTy(8),
+             "wrong type for intrinsic global variable", &GV);
     }
   }