From 59b4a555c3f1c3dba376da1c4886a9ea18ad208d Mon Sep 17 00:00:00 2001 From: Hans-Peter Nilsson Date: Tue, 14 Mar 2023 02:06:34 +0100 Subject: [PATCH] doc: md.texi (Insn Splitting): Tweak wording for readability. 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 --- 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 edfa51e867a8..970af5e34710 100644 --- a/gcc/doc/md.texi +++ b/gcc/doc/md.texi @@ -8767,21 +8767,21 @@ 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 -- 2.47.2