> From: Hans-Peter Nilsson <[email protected]>
> Date: Wed, 19 Apr 2023 18:59:14 +0200
[...]
> So again: Approvers: pdf output reviewed. Ok to commit?
> -- >8 --
> I was a bit surprised when my newly-added define_peephole2 didn't
> match, but it was because it was expected to partially match the
> generated output of a previous define_peephole2, which matched and
> modified the last insn of a sequence to be matched. I had assumed
> that the algorithm backed-up the size of the match-buffer, thereby
> exposing newly created opportunities *with sufficient context* to all
> define_peephole2's. While things can change in that direction, let's
> start with documenting the current state.
>
> * doc/md.texi (define_peephole2): Document order of scanning.
> ---
> gcc/doc/md.texi | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
> index 07bf8bdebffb..300d104d58ab 100644
> --- a/gcc/doc/md.texi
> +++ b/gcc/doc/md.texi
> @@ -9362,6 +9362,15 @@ If the preparation falls through (invokes neither
> @code{DONE} nor
> @code{FAIL}), then the @code{define_peephole2} uses the replacement
> template.
>
> +Insns are scanned in forward order from beginning to end for each basic
> +block. Matches are attempted in order of @code{define_peephole2}
> +appearance in the @file{md} file. After a successful replacement,
> +scanning for further opportunities for @code{define_peephole2}, resumes
> +with the first generated replacement insn as the first insn to be
> +matched against all @code{define_peephole2}. For the example above,
> +after its successful replacement, the first insn that can be matched by
> +a @code{define_peephole2} is @code{(set (match_dup 4) (match_dup 1))}.
> +
> @end ifset
> @ifset INTERNALS
> @node Insn Attributes
> --
> 2.30.2
>
