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| author | Hans-Peter Nilsson <hp@axis.com> | 2023-04-18 19:37:21 +0200 |
|---|---|---|
| committer | Hans-Peter Nilsson <hp@bitrange.com> | 2023-05-06 01:10:37 +0200 |
| commit | 07527e3eabb00ada0e7c9e083084e4e56d97f34f (patch) | |
| tree | 12b8a30b840cb9ff276061fdd3b11dafc6c47403 /gcc | |
| parent | 185da7c2014ba41f38dd62cc719873ebf020b076 (diff) | |
| download | gcc-07527e3eabb00ada0e7c9e083084e4e56d97f34f.zip gcc-07527e3eabb00ada0e7c9e083084e4e56d97f34f.tar.gz gcc-07527e3eabb00ada0e7c9e083084e4e56d97f34f.tar.bz2 | |
doc: Document order of define_peephole2 scanning
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.
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/doc/md.texi | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi index cc4a93a..37e5377 100644 --- a/gcc/doc/md.texi +++ b/gcc/doc/md.texi @@ -9371,6 +9371,15 @@ 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 |