Clarify the meaning of the symbol_value instruction.

lib/codegen/meta-python/base/instructions.py

@@ -502,15 +502,15 @@ global_value = Instruction(
         'global_value', r"""
         Compute the value of global GV.
         """,
-        ins=GV, outs=addr)
+        ins=GV, outs=a)
 
 # A specialized form of global_value instructions that only handles
 # symbolic names.
 symbol_value = Instruction(
         'symbol_value', r"""
-        Compute the value of global GV, which is a symbolic address.
+        Compute the value of global GV, which is a symbolic value.
         """,
-        ins=GV, outs=addr)
+        ins=GV, outs=a)
 
 #
 # WebAssembly bounds-checked heap accesses.

lib/codegen/src/ir/globalvalue.rs

@@ -39,8 +39,13 @@ pub enum GlobalValueData {
         global_type: Type,
     },
 
-    /// Value is a symbolic address. Cranelift itself does not interpret this name;
-    /// it's used by embedders to link with other data structures.
+    /// Value is symbolic, meaning it's a name which will be resolved to an
+    /// actual value later (eg. by linking). Cranelift itself does not interpret
+    /// this name; it's used by embedders to link with other data structures.
+    ///
+    /// For now, symbolic values always have pointer type, and represent
+    /// addresses, however in the future they could be used to represent other
+    /// things as well.
     Symbol {
         /// The symbolic name.
         name: ExternalName,