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* [Bug tree-optimization/102676] New: Failure to optimize out malloc/nothrow allocation that's only used for bool checking @ 2021-10-10 3:07 gabravier at gmail dot com 2021-10-10 6:26 ` [Bug tree-optimization/102676] " schwab@linux-m68k.org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: gabravier at gmail dot com @ 2021-10-10 3:07 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102676 Bug ID: 102676 Summary: Failure to optimize out malloc/nothrow allocation that's only used for bool checking Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: gabravier at gmail dot com Target Milestone: --- #include <new> #include <stdlib.h> bool f() { return new(std::nothrow) int; } bool g() { return malloc(1); } Both these functions can be optimized to `return true;`. This optimization is done by LLVM, but not by GCC. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/102676] Failure to optimize out malloc/nothrow allocation that's only used for bool checking 2021-10-10 3:07 [Bug tree-optimization/102676] New: Failure to optimize out malloc/nothrow allocation that's only used for bool checking gabravier at gmail dot com @ 2021-10-10 6:26 ` schwab@linux-m68k.org 2021-10-10 13:50 ` gabravier at gmail dot com 2021-10-11 9:07 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: schwab@linux-m68k.org @ 2021-10-10 6:26 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102676 --- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> --- Why is malloc(1) always true? ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/102676] Failure to optimize out malloc/nothrow allocation that's only used for bool checking 2021-10-10 3:07 [Bug tree-optimization/102676] New: Failure to optimize out malloc/nothrow allocation that's only used for bool checking gabravier at gmail dot com 2021-10-10 6:26 ` [Bug tree-optimization/102676] " schwab@linux-m68k.org @ 2021-10-10 13:50 ` gabravier at gmail dot com 2021-10-11 9:07 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: gabravier at gmail dot com @ 2021-10-10 13:50 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102676 --- Comment #2 from Gabriel Ravier <gabravier at gmail dot com> --- Well, I think the assumption LLVM is making is that the allocation, being unused, can just be eliminated and considered to have always succeeded. I don't see how that would contradict the standard, although I suppose some would consider it a bad thing to do for the compiler (although in that case you might as well rule out all optimizations that elide allocations). ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/102676] Failure to optimize out malloc/nothrow allocation that's only used for bool checking 2021-10-10 3:07 [Bug tree-optimization/102676] New: Failure to optimize out malloc/nothrow allocation that's only used for bool checking gabravier at gmail dot com 2021-10-10 6:26 ` [Bug tree-optimization/102676] " schwab@linux-m68k.org 2021-10-10 13:50 ` gabravier at gmail dot com @ 2021-10-11 9:07 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu.org @ 2021-10-11 9:07 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102676 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Last reconfirmed| |2021-10-11 Ever confirmed|0 |1 Status|UNCONFIRMED |NEW --- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- We don't eliminate a malloc that's just used in a conditional, I think there's a related bugreport with p = malloc (n) if (!p) abort (); free (p); or sth like that where we fail to elide the allocation. Note in this case failing allocation _would_ have a side-effect. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-10-11 9:07 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-10-10 3:07 [Bug tree-optimization/102676] New: Failure to optimize out malloc/nothrow allocation that's only used for bool checking gabravier at gmail dot com 2021-10-10 6:26 ` [Bug tree-optimization/102676] " schwab@linux-m68k.org 2021-10-10 13:50 ` gabravier at gmail dot com 2021-10-11 9:07 ` rguenth at gcc dot gnu.org
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