[GCRoot] Assert preconditions to clarify behavior

This code isn't reachable if the GFI (GCFunctionInfo*) is null.  Clarify this by adding an assert and removing an always taken if.  

llvm-svn: 257724

1 files changed, 12 insertions, 8 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 45ae39af760..59811107a6c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5060,15 +5060,19 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
                              getValue(I.getArgOperand(0))));
     return nullptr;
   }
-  case Intrinsic::gcroot:
-    if (GFI) {
-      const Value *Alloca = I.getArgOperand(0)->stripPointerCasts();
-      const Constant *TypeMap = cast<Constant>(I.getArgOperand(1));
-
-      FrameIndexSDNode *FI = cast<FrameIndexSDNode>(getValue(Alloca).getNode());
-      GFI->addStackRoot(FI->getIndex(), TypeMap);
-    }
+  case Intrinsic::gcroot: {
+    MachineFunction &MF = DAG.getMachineFunction();
+    const Function *F = MF.getFunction();
+    assert(F->hasGC() &&
+           "only valid in functions with gc specified, enforced by Verifier");
+    assert(GFI && "implied by previous");
+    const Value *Alloca = I.getArgOperand(0)->stripPointerCasts();
+    const Constant *TypeMap = cast<Constant>(I.getArgOperand(1));
+
+    FrameIndexSDNode *FI = cast<FrameIndexSDNode>(getValue(Alloca).getNode());
+    GFI->addStackRoot(FI->getIndex(), TypeMap);
     return nullptr;
+  }
   case Intrinsic::gcread:
   case Intrinsic::gcwrite:
     llvm_unreachable("GC failed to lower gcread/gcwrite intrinsics!");