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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) -- links below jump to the message on this page -- 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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