Re: [PATCH v2] doc: md.texi (Insn Splitting): Tweak wording for readability.

[Hans-Peter Nilsson <hp@axis.com>]

> From: Hans-Peter Nilsson <hp@axis.com>
> CC: <gcc-patches@gcc.gnu.org>, <hubicka@ucw.cz>
> Date: Tue, 14 Mar 2023 17:04:43 +0100

Ping on contents (formatting is approved):

> I needed to check what was allowed in a define_split, but
> had problems understanding what was meant by "Splitting of
> jump instruction into sequence that over by another jump
> instruction".
> 
> 	* doc/md.texi (Insn Splitting): Tweak wording for readability.
> 
> Co-Authored-By: Sandra Loosemore <sandra@codesourcery.com>
> ---
>  gcc/doc/md.texi | 30 +++++++++++++++---------------
>  1 file changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
> index 8e3113599fdc..134b227b9a93 100644
> --- a/gcc/doc/md.texi
> +++ b/gcc/doc/md.texi
> @@ -8756,21 +8756,21 @@ insns that don't.  Instead, write two separate @code{define_split}
>  definitions, one for the insns that are valid and one for the insns that
>  are not valid.
>  
> -The splitter is allowed to split jump instructions into sequence of
> -jumps or create new jumps in while splitting non-jump instructions.  As
> -the control flow graph and branch prediction information needs to be updated,
> -several restriction apply.
> -
> -Splitting of jump instruction into sequence that over by another jump
> -instruction is always valid, as compiler expect identical behavior of new
> -jump.  When new sequence contains multiple jump instructions or new labels,
> -more assistance is needed.  Splitter is required to create only unconditional
> -jumps, or simple conditional jump instructions.  Additionally it must attach a
> -@code{REG_BR_PROB} note to each conditional jump.  A global variable
> -@code{split_branch_probability} holds the probability of the original branch in case
> -it was a simple conditional jump, @minus{}1 otherwise.  To simplify
> -recomputing of edge frequencies, the new sequence is required to have only
> -forward jumps to the newly created labels.
> +The splitter is allowed to split jump instructions into a sequence of jumps or
> +create new jumps while splitting non-jump instructions.  As the control flow
> +graph and branch prediction information needs to be updated after the splitter
> +runs, several restrictions apply.
> +
> +Splitting of a jump instruction into a sequence that has another jump
> +instruction to the same label is always valid, as the compiler expects
> +identical behavior of the new jump.  When the new sequence contains multiple
> +jump instructions or new labels, more assistance is needed.  The splitter is
> +permitted to create only unconditional jumps, or simple conditional jump
> +instructions.  Additionally it must attach a @code{REG_BR_PROB} note to each
> +conditional jump.  A global variable @code{split_branch_probability} holds the
> +probability of the original branch in case it was a simple conditional jump,
> +@minus{}1 otherwise.  To simplify recomputing of edge frequencies, the new
> +sequence is permitted to have only forward jumps to the newly-created labels.
>  
>  @findex define_insn_and_split
>  For the common case where the pattern of a define_split exactly matches the
> -- 
> 2.30.2
> 
> brgds, H-P
>