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* [Bug c/67979] New: dead code elimination deleted the predicated branch within the function block.
@ 2015-10-15 19:30 feqin1023 at gmail dot com
2015-10-15 19:42 ` [Bug c/67979] " pinskia at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: feqin1023 at gmail dot com @ 2015-10-15 19:30 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67979
Bug ID: 67979
Summary: dead code elimination deleted the predicated branch
within the function block.
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: feqin1023 at gmail dot com
Target Milestone: ---
Created attachment 36518
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36518&action=edit
the source test dead code elimination.
if i have this input:
/*--------------------test.c----------------------------*/
void bar_i(int);
void foo(int *x) {
int y = *x; // dead code can be clean
if (!x)
return; // this branch ALSO will be clean
bar_i(y);
}
/*------------------------------------------------------*/
we call gcc like this:
gcc -O2 -S test.c
the the whole branch in function foo(int *) will be clean.
BUT, if foo(int *) is called like this:
foo(NULL);
gcc has CHANGED the original semantic even sometimes which
is error. but compiler can do this?
I also test Clang, Clang ALWAYS keep the branch in foo(int *).
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/67979] dead code elimination deleted the predicated branch within the function block.
2015-10-15 19:30 [Bug c/67979] New: dead code elimination deleted the predicated branch within the function block feqin1023 at gmail dot com
@ 2015-10-15 19:42 ` pinskia at gcc dot gnu.org
2015-10-15 20:09 ` feqin1023 at gmail dot com
2015-10-16 7:49 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2015-10-15 19:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67979
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The code is undefined if NULL is passed and that is why the branch is removed.
If you don't want this optimization then use -fno-delete-null-pointer-checks
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/67979] dead code elimination deleted the predicated branch within the function block.
2015-10-15 19:30 [Bug c/67979] New: dead code elimination deleted the predicated branch within the function block feqin1023 at gmail dot com
2015-10-15 19:42 ` [Bug c/67979] " pinskia at gcc dot gnu.org
@ 2015-10-15 20:09 ` feqin1023 at gmail dot com
2015-10-16 7:49 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: feqin1023 at gmail dot com @ 2015-10-15 20:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67979
zet <feqin1023 at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |CLOSED
Resolution|INVALID |FIXED
--- Comment #2 from zet <feqin1023 at gmail dot com> ---
(In reply to Andrew Pinski from comment #1)
> The code is undefined if NULL is passed and that is why the branch is
> removed. If you don't want this optimization then use
> -fno-delete-null-pointer-checks
Well, it's a feature.
Thx.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/67979] dead code elimination deleted the predicated branch within the function block.
2015-10-15 19:30 [Bug c/67979] New: dead code elimination deleted the predicated branch within the function block feqin1023 at gmail dot com
2015-10-15 19:42 ` [Bug c/67979] " pinskia at gcc dot gnu.org
2015-10-15 20:09 ` feqin1023 at gmail dot com
@ 2015-10-16 7:49 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: rguenth at gcc dot gnu.org @ 2015-10-16 7:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67979
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
*** Bug 67978 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2015-10-16 7:49 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2015-10-15 19:30 [Bug c/67979] New: dead code elimination deleted the predicated branch within the function block feqin1023 at gmail dot com
2015-10-15 19:42 ` [Bug c/67979] " pinskia at gcc dot gnu.org
2015-10-15 20:09 ` feqin1023 at gmail dot com
2015-10-16 7:49 ` rguenth at gcc dot gnu.org
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