diff options
| author | Ludovic Courtès <ludo@gnu.org> | 2021-09-21 09:43:53 +0200 |
|---|---|---|
| committer | Ludovic Courtès <ludo@gnu.org> | 2021-09-21 15:15:52 +0200 |
| commit | baa0aa1348aa5fe526425efbf11707d8e02a2640 (patch) | |
| tree | 0af55bcc4cebb576b4f463456e0210ec1a885666 /guix/base32.scm | |
| parent | 39414b78d8a5b6fc9a4fdecb0551d822c1ffe49d (diff) | |
| download | guix-baa0aa1348aa5fe526425efbf11707d8e02a2640.tar guix-baa0aa1348aa5fe526425efbf11707d8e02a2640.tar.gz | |
base32: Work around (ash x N) miscompilation at '-O1' and below.
Fixes <https://issues.guix.gnu.org/50696>.
Reported by Marius Bakke <marius@gnu.org>.
* guix/base32.scm (bit-field): Introduce 'minus-start' syntax and use it.
Diffstat (limited to 'guix/base32.scm')
| -rw-r--r-- | guix/base32.scm | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/guix/base32.scm b/guix/base32.scm index d6c8a02243..8f097d4e77 100644 --- a/guix/base32.scm +++ b/guix/base32.scm @@ -53,7 +53,15 @@ (let* ((s (syntax->datum #'start)) (e (syntax->datum #'end)) (mask (- (expt 2 (- e s)) 1))) - #`(logand (ash n (- start)) #,mask)))))) + ;; The baseline compiler in Guile <= 3.0.7 miscompiles (ash x N) as + ;; (ash x (- N)) when N is a literal: <https://bugs.gnu.org/50696>. + ;; Here we take advantage of another bug in the baseline compiler, + ;; fixed in Guile commit 330c6ea83f492672578b62d0683acbb532d1a5d9: we + ;; introduce 'minus-start' such that it has a different source + ;; location, which in turn means that the baseline compiler pattern + ;; for (ash x N) doesn't match, thus avoiding the bug (!). + (with-syntax ((minus-start (datum->syntax #'start (- s)))) + #`(logand (ash n minus-start) #,mask))))))) (define bytevector-quintet-ref (let* ((ref bytevector-u8-ref) |