From 7a18d752e7061c81f83f97969ecf5cd46379d51e Mon Sep 17 00:00:00 2001 From: Richard Biener Date: Fri, 7 Oct 2016 11:26:15 +0000 Subject: [PATCH] bitmap.h: Document constraints on bitmap modification while iterating over it. 2016-10-07 Richard Biener * bitmap.h: Document constraints on bitmap modification while iterating over it. From-SVN: r240860 --- gcc/ChangeLog | 5 +++++ gcc/bitmap.h | 12 ++++++++++++ 2 files changed, 17 insertions(+) diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 56e5fd9a1b5..15315eb39eb 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,8 @@ +2016-10-07 Richard Biener + + * bitmap.h: Document constraints on bitmap modification while + iterating over it. + 2016-10-07 Richard Biener * bitmap.c (bitmap_elem_to_freelist): Set indx to -1. diff --git a/gcc/bitmap.h b/gcc/bitmap.h index e4e80d6ce5d..1b2c8e0c13c 100644 --- a/gcc/bitmap.h +++ b/gcc/bitmap.h @@ -755,6 +755,18 @@ bmp_iter_and_compl (bitmap_iterator *bi, unsigned *bit_no) } } +/* If you are modifying a bitmap you are currently iterating over you + have to ensure to + - never remove the current bit; + - if you set or clear a bit before the current bit this operation + will not affect the set of bits you are visiting during the iteration; + - if you set or clear a bit after the current bit it is unspecified + whether that affects the set of bits you are visiting during the + iteration. + If you want to remove the current bit you can delay this to the next + iteration (and after the iteration in case the last iteration is + affected). */ + /* Loop over all bits set in BITMAP, starting with MIN and setting BITNUM to the bit number. ITER is a bitmap iterator. BITNUM should be treated as a read-only variable as it contains loop -- 2.30.2