In doing CCmode work I was confused how define_subst handles cases where the
same argument appears more than once. The attached clarifies this.
Ok for trunk?
paul
ChangeLog:
2018-07-08 Paul Koning <n...@arrl.net>
* doc/md.texi (define_subst): Document how multiple occurrences of
the same argument in the replacement pattern are handled.
Index: doc/md.texi
===================================================================
--- doc/md.texi (revision 262505)
+++ doc/md.texi (working copy)
@@ -10263,7 +10263,11 @@ the expression from the original pattern, which ma
@code{match_operand N} from the input pattern. As a consequence,
@code{match_dup} cannot be used to point to @code{match_operand}s from
the output pattern, it should always refer to a @code{match_operand}
-from the input pattern.
+from the input pattern. If a @code{match_dup N} occurs more than once
+in the output template, its first occurrence is replaced with the
+expression from the original pattern, and the subsequent expressions
+are replaced with @code{match_dup N}, i.e., a reference to the first
+expression.
In the output template one can refer to the expressions from the
original pattern and create new ones. For instance, some operands could
