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* [Bug middle-end/23669] New: fold does convert (-a)/10 into a/-10. @ 2005-09-01 2:04 pinskia at gcc dot gnu dot org 2005-09-01 2:38 ` [Bug middle-end/23669] " pinskia at gcc dot gnu dot org ` (3 more replies) 0 siblings, 4 replies; 5+ messages in thread From: pinskia at gcc dot gnu dot org @ 2005-09-01 2:04 UTC (permalink / raw) To: gcc-bugs Another idea from LLVM. The following two functions should be the same asm: int f(int a) { return (-a)/10; } int f1(int a) { return a/-10; } ---- We currently get on PPC: _f: lis r0,0x6666 neg r3,r3 ori r0,r0,26215 mulhw r0,r3,r0 srawi r3,r3,31 srawi r0,r0,2 subf r3,r3,r0 blr _f1: lis r0,0x6666 ori r0,r0,26215 mulhw r0,r3,r0 srawi r3,r3,31 srawi r0,r0,2 subf r3,r0,r3 blr As you can see f1 has one less instruction which should be better. -- Summary: fold does convert (-a)/10 into a/-10. Product: gcc Version: 4.1.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P2 Component: middle-end AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: pinskia at gcc dot gnu dot org CC: gcc-bugs at gcc dot gnu dot org OtherBugsDependingO 19987 nThis: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23669 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/23669] fold does convert (-a)/10 into a/-10. 2005-09-01 2:04 [Bug middle-end/23669] New: fold does convert (-a)/10 into a/-10 pinskia at gcc dot gnu dot org @ 2005-09-01 2:38 ` pinskia at gcc dot gnu dot org 2005-09-17 2:12 ` pinskia at gcc dot gnu dot org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu dot org @ 2005-09-01 2:38 UTC (permalink / raw) To: gcc-bugs -- What |Removed |Added ---------------------------------------------------------------------------- Severity|normal |enhancement http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23669 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/23669] fold does convert (-a)/10 into a/-10. 2005-09-01 2:04 [Bug middle-end/23669] New: fold does convert (-a)/10 into a/-10 pinskia at gcc dot gnu dot org 2005-09-01 2:38 ` [Bug middle-end/23669] " pinskia at gcc dot gnu dot org @ 2005-09-17 2:12 ` pinskia at gcc dot gnu dot org 2005-10-01 17:25 ` mrnobo1024 at yahoo dot com 2005-10-01 17:34 ` [Bug middle-end/23669] fold does convert (-a)/10 into a/-10 with -fno-wrapv pinskia at gcc dot gnu dot org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu dot org @ 2005-09-17 2:12 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From pinskia at gcc dot gnu dot org 2005-09-17 02:12 ------- Confirmed. -- What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Ever Confirmed| |1 Last reconfirmed|0000-00-00 00:00:00 |2005-09-17 02:12:00 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23669 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/23669] fold does convert (-a)/10 into a/-10. 2005-09-01 2:04 [Bug middle-end/23669] New: fold does convert (-a)/10 into a/-10 pinskia at gcc dot gnu dot org 2005-09-01 2:38 ` [Bug middle-end/23669] " pinskia at gcc dot gnu dot org 2005-09-17 2:12 ` pinskia at gcc dot gnu dot org @ 2005-10-01 17:25 ` mrnobo1024 at yahoo dot com 2005-10-01 17:34 ` [Bug middle-end/23669] fold does convert (-a)/10 into a/-10 with -fno-wrapv pinskia at gcc dot gnu dot org 3 siblings, 0 replies; 5+ messages in thread From: mrnobo1024 at yahoo dot com @ 2005-10-01 17:25 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From mrnobo1024 at yahoo dot com 2005-10-01 17:25 ------- Those expressions are only the same for floating point types. f(-2147483648) == -214748364 f1(-2147483648) == 214748364 -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23669 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/23669] fold does convert (-a)/10 into a/-10 with -fno-wrapv 2005-09-01 2:04 [Bug middle-end/23669] New: fold does convert (-a)/10 into a/-10 pinskia at gcc dot gnu dot org ` (2 preceding siblings ...) 2005-10-01 17:25 ` mrnobo1024 at yahoo dot com @ 2005-10-01 17:34 ` pinskia at gcc dot gnu dot org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu dot org @ 2005-10-01 17:34 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From pinskia at gcc dot gnu dot org 2005-10-01 17:34 ------- (In reply to comment #2) > Those expressions are only the same for floating point types. But -a for INT_MIN is undefined for signed type since it is an overflow. So the conversion is only valid for -fno-wrapv which is default for C, C++, Ada, and fortran. -- What |Removed |Added ---------------------------------------------------------------------------- Summary|fold does convert (-a)/10 |fold does convert (-a)/10 |into a/-10. |into a/-10 with -fno-wrapv http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23669 ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2005-10-01 17:34 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2005-09-01 2:04 [Bug middle-end/23669] New: fold does convert (-a)/10 into a/-10 pinskia at gcc dot gnu dot org 2005-09-01 2:38 ` [Bug middle-end/23669] " pinskia at gcc dot gnu dot org 2005-09-17 2:12 ` pinskia at gcc dot gnu dot org 2005-10-01 17:25 ` mrnobo1024 at yahoo dot com 2005-10-01 17:34 ` [Bug middle-end/23669] fold does convert (-a)/10 into a/-10 with -fno-wrapv pinskia at gcc dot gnu dot org
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