Verify ref metadata node is not placed on a declaration.

Author: mandlebug

llvm/lib/IR/Verifier.cpp

@@ -771,6 +771,9 @@ void Verifier::visitGlobalValue(const GlobalValue &GV) {
     }
 
     if (GO->hasMetadata(LLVMContext::MD_ref)) {
+      Check(!GO->isDeclaration(),
+            "ref metadata must not be placed on a declaration", GO);
+
       SmallVector<MDNode *> MDs;
       GO->getMetadata(LLVMContext::MD_ref, MDs);
       for (const MDNode *MD : MDs) {

llvm/test/Verifier/ref.ll

@@ -4,6 +4,7 @@
 @b = global i32 2, !ref !1
 @c = global i32 3, !ref !1, !ref !2
 @d = global i32 4, !ref !3
+@e = external global i32, !ref !1
 
 !0 = !{i32 1}
 !1 = !{ptr @b}
@@ -25,3 +26,6 @@
 ; CHECK: ref metadata must have one operand
 ; CHECK: ptr @d
 ; CHECK: !3 = !{ptr @c, ptr @a}
+
+; CHECK: ref metadata must not be placed on a declaration
+; CHECK: @e