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* [Bug target/108371] New: gcc for x86_64 may sign/zero extent arguments unnecessarily
@ 2023-01-11 14:04 dhowells at redhat dot com
2023-01-11 14:28 ` [Bug target/108371] " rguenth at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: dhowells at redhat dot com @ 2023-01-11 14:04 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108371
Bug ID: 108371
Summary: gcc for x86_64 may sign/zero extent arguments
unnecessarily
Product: gcc
Version: 12.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: dhowells at redhat dot com
Target Milestone: ---
When compiling for x86_64, bool, char and short arguments that are passed
directly to an argument of exactly the same type on another function with no
modification, e.g.:
void __bio_release_pages(char mark_dirty);
void bio_release_pages(char mark_dirty)
{
__bio_release_pages(mark_dirty);
}
get sign/zero-extended unnecessarily. In the case of the above code, it
compiles to:
0: 40 0f be ff movsbl %dil,%edi
4: e9 00 00 00 00 jmp 9 <bio_release_pages+0x9>
with "gcc -Os -c test.c". Can the extension be optimised away? Granted, the
upper bits bits of RDI could contain rubbish on entry to bio_release_pages(),
so sanitisation is not unreasonable - but on the other hand,
__bio_release_pages() would surely have to assume the same and do the same
sanitisation?
The toolchain used is the Fedora 37 system compiler:
gcc-12.2.1-4.fc37.x86_64
binutils-2.38-25.fc37.x86_64
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug target/108371] gcc for x86_64 may sign/zero extent arguments unnecessarily
2023-01-11 14:04 [Bug target/108371] New: gcc for x86_64 may sign/zero extent arguments unnecessarily dhowells at redhat dot com
@ 2023-01-11 14:28 ` rguenth at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-01-11 14:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108371
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target| |x86_64-*-*
Status|UNCONFIRMED |NEW
Last reconfirmed| |2023-01-11
Keywords| |missed-optimization
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. This is the C frontend doing
;; Function bio_release_pages (null)
;; enabled by -tree-original
{
__bio_release_pages ((int) mark_dirty);
}
aka targetm.calls.promote_prototypes
^ permalink raw reply [flat|nested] 2+ messages in thread
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2023-01-11 14:04 [Bug target/108371] New: gcc for x86_64 may sign/zero extent arguments unnecessarily dhowells at redhat dot com
2023-01-11 14:28 ` [Bug target/108371] " rguenth at gcc dot gnu.org
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