Require members of llvm.used to be named.

The effect of llvm.used is to introduce an invisible reference, so this seems
a reasonable restriction. It will be used to provide an easy ordering of
the entries in llvm.used.

llvm-svn: 183743

llvm/docs/LangRef.rst

@@ -2932,8 +2932,8 @@ The '``llvm.used``' Global Variable
 
 The ``@llvm.used`` global is an array which has
 :ref:`appending linkage <linkage_appending>`. This array contains a list of
-pointers to global variables, functions and aliases which may optionally have a
-pointer cast formed of bitcast or getelementptr. For example, a legal
+pointers to named global variables, functions and aliases which may optionally
+have a pointer cast formed of bitcast or getelementptr. For example, a legal
 use of it is:
 
 .. code-block:: llvm
@@ -2948,11 +2948,11 @@ use of it is:
 
 If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler,
 and linker are required to treat the symbol as if there is a reference to the
-symbol that it cannot see. For example, if a variable has internal linkage and
-no references other than that from the ``@llvm.used`` list, it cannot be
-deleted. This is commonly used to represent references from inline asms and
-other things the compiler cannot "see", and corresponds to
-"``attribute((used))``" in GNU C.
+symbol that it cannot see (which is why they have to be named). For example, if
+a variable has internal linkage and no references other than that from the
+``@llvm.used`` list, it cannot be deleted. This is commonly used to represent
+references from inline asms and other things the compiler cannot "see", and
+corresponds to "``attribute((used))``" in GNU C.
 
 On some targets, the code generator must emit a directive to the
 assembler or object file to prevent the assembler and linker from

llvm/lib/IR/Verifier.cpp

@@ -467,6 +467,7 @@ void Verifier::visitGlobalVariable(GlobalVariable &GV) {
           Assert1(
               isa<GlobalVariable>(V) || isa<Function>(V) || isa<GlobalAlias>(V),
               "invalid llvm.used member", V);
+          Assert1(V->hasName(), "members of llvm.used must be named", V);
         }
       }
     }