Improve dumping for rules, and documentation of same

Inspired by Trac #3703

compiler/simplCore/SimplCore.lhs

@@ -323,9 +323,9 @@ prepareRules hsc_env@(HscEnv { hsc_dflags = dflags, hsc_HPT = hpt })
 
 	; Err.dumpIfSet_dyn dflags Opt_D_dump_rules "Transformation rules"
 		(withPprStyle (mkUserStyle (mkPrintUnqualified dflags rdr_env) AllTheWay) $
-		 vcat [text "Local rules", pprRules simpl_rules,
+		 vcat [text "Local rules for local Ids", pprRules simpl_rules,
 		       blankLine,
-		       text "Imported rules", pprRuleBase hpt_rule_base])
+		       text "Local rules for imported Ids", pprRuleBase hpt_rule_base])
 
 	; return (hpt_rule_base, guts { mg_binds = binds_w_rules, 
 					mg_rules = rules_for_imps })

docs/users_guide/debugging.xml

@@ -120,8 +120,9 @@
                 <indexterm><primary><option>-ddump-rules</option></primary></indexterm>
 	      </term>
 	      <listitem>
-		<para>dumps all rewrite rules (including those generated
-	      by the specialisation pass)</para>
+		<para>dumps all rewrite rules specified in this module; 
+                      see <xref linkend="controlling-rules"/>.
+                </para>
 	      </listitem>
 	    </varlistentry>
 

docs/users_guide/glasgow_exts.xml

@@ -8605,8 +8605,8 @@ comparison.
 
 </sect2>
 
-<sect2>
-<title>Controlling what's going on</title>
+<sect2 id="controlling-rules">
+<title>Controlling what's going on in rewrite rules</title>
 
 <para>
 
@@ -8614,7 +8614,10 @@ comparison.
 <listitem>
 
 <para>
- Use <option>-ddump-rules</option> to see what transformation rules GHC is using.
+Use <option>-ddump-rules</option> to see the rules that are defined
+<emphasis>in this module</emphasis>.
+This includes rules generated by the specialisation pass, but excludes
+rules imported from other modules. 
 </para>
 </listitem>