> On Jul 6, 2018, at 12:20 PM, Richard Sandiford <richard.sandif...@arm.com>
> wrote:
>
> Double empty line.
>
> OK otherwise, thanks. (Think this counts as a gen* patch.)
>
> Richard
Thanks. Committed as shown below.
paul
ChangeLog:
2018-07-06 Paul Koning <n...@arrl.net>
* doc/md.texi (define_split): Document DONE and FAIL.
(define_peephole2): Ditto.
Index: doc/md.texi
===================================================================
--- doc/md.texi (revision 262478)
+++ doc/md.texi (working copy)
@@ -8060,6 +8060,30 @@ those in @code{define_expand}, however, these stat
generate any new pseudo-registers. Once reload has completed, they also
must not allocate any space in the stack frame.
+There are two special macros defined for use in the preparation statements:
+@code{DONE} and @code{FAIL}. Use them with a following semicolon,
+as a statement.
+
+@table @code
+
+@findex DONE
+@item DONE
+Use the @code{DONE} macro to end RTL generation for the splitter. The
+only RTL insns generated as replacement for the matched input insn will
+be those already emitted by explicit calls to @code{emit_insn} within
+the preparation statements; the replacement pattern is not used.
+
+@findex FAIL
+@item FAIL
+Make the @code{define_split} fail on this occasion. When a @code{define_split}
+fails, it means that the splitter was not truly available for the inputs
+it was given, and the input insn will not be split.
+@end table
+
+If the preparation falls through (invokes neither @code{DONE} nor
+@code{FAIL}), then the @code{define_split} uses the replacement
+template.
+
Patterns are matched against @var{insn-pattern} in two different
circumstances. If an insn needs to be split for delay slot scheduling
or insn scheduling, the insn is already known to be valid, which means
@@ -8615,6 +8639,33 @@ so here's a silly made-up example:
"")
@end smallexample
+There are two special macros defined for use in the preparation statements:
+@code{DONE} and @code{FAIL}. Use them with a following semicolon,
+as a statement.
+
+@table @code
+
+@findex DONE
+@item DONE
+Use the @code{DONE} macro to end RTL generation for the peephole. The
+only RTL insns generated as replacement for the matched input insn will
+be those already emitted by explicit calls to @code{emit_insn} within
+the preparation statements; the replacement pattern is not used.
+
+@findex FAIL
+@item FAIL
+Make the @code{define_peephole2} fail on this occasion. When a
@code{define_peephole2}
+fails, it means that the replacement was not truly available for the
+particular inputs it was given. In that case, GCC may still apply a
+later @code{define_peephole2} that also matches the given insn pattern.
+(Note that this is different from @code{define_split}, where @code{FAIL}
+prevents the input insn from being split at all.)
+@end table
+
+If the preparation falls through (invokes neither @code{DONE} nor
+@code{FAIL}), then the @code{define_peephole2} uses the replacement
+template.
+
@noindent
If we had not added the @code{(match_dup 4)} in the middle of the input
sequence, it might have been the case that the register we chose at the
