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* [Bug other/17103] New: Opportunity to replace multiply with shift/add sequence @ 2004-08-19 14:59 gcc-bugzilla at gcc dot gnu dot org 2004-08-19 15:34 ` [Bug middle-end/17103] " pinskia at gcc dot gnu dot org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: gcc-bugzilla at gcc dot gnu dot org @ 2004-08-19 14:59 UTC (permalink / raw) To: gcc-bugs Description: A non-optimal code sequence is illustraded. Duplicate using gcc 3.5 and command line: gcc -O3 -m32 -c test.c Testcase: long foo(long x) { return (x * 258); } Assembly: Currently, gcc 3.5 generates the following: foo: mulli 3,3,258 blr It would be more efficient to use a shift/add sequence: foo: or 0,3,3 rlwinm 3,3,8 add 0,0,0 add 3,3,0 blr -- Summary: Opportunity to replace multiply with shift/add sequence Product: gcc Version: 3.5.0 Status: UNCONFIRMED Severity: enhancement Priority: P1 Component: other AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: steinmtz at us dot ibm dot com CC: gcc-bugs at gcc dot gnu dot org,steinmtz at us dot ibm dot com GCC build triplet: powerpc64-linux GCC host triplet: powerpc64-linux GCC target triplet: powerpc64-linux http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17103 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/17103] Opportunity to replace multiply with shift/add sequence 2004-08-19 14:59 [Bug other/17103] New: Opportunity to replace multiply with shift/add sequence gcc-bugzilla at gcc dot gnu dot org @ 2004-08-19 15:34 ` pinskia at gcc dot gnu dot org 2004-08-19 15:46 ` [Bug target/17103] " falk at debian dot org 2004-09-12 20:37 ` dje at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu dot org @ 2004-08-19 15:34 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From pinskia at gcc dot gnu dot org 2004-08-19 15:34 ------- Confirmed. -- What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Component|other |middle-end Ever Confirmed| |1 Keywords| |missed-optimization Last reconfirmed|0000-00-00 00:00:00 |2004-08-19 15:34:29 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17103 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/17103] Opportunity to replace multiply with shift/add sequence 2004-08-19 14:59 [Bug other/17103] New: Opportunity to replace multiply with shift/add sequence gcc-bugzilla at gcc dot gnu dot org 2004-08-19 15:34 ` [Bug middle-end/17103] " pinskia at gcc dot gnu dot org @ 2004-08-19 15:46 ` falk at debian dot org 2004-09-12 20:37 ` dje at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: falk at debian dot org @ 2004-08-19 15:46 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From falk at debian dot org 2004-08-19 15:46 ------- This works on Alpha, so I guess it is something target specific, like imprecise insn costs. -- What |Removed |Added ---------------------------------------------------------------------------- Component|middle-end |target http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17103 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/17103] Opportunity to replace multiply with shift/add sequence 2004-08-19 14:59 [Bug other/17103] New: Opportunity to replace multiply with shift/add sequence gcc-bugzilla at gcc dot gnu dot org 2004-08-19 15:34 ` [Bug middle-end/17103] " pinskia at gcc dot gnu dot org 2004-08-19 15:46 ` [Bug target/17103] " falk at debian dot org @ 2004-09-12 20:37 ` dje at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: dje at gcc dot gnu dot org @ 2004-09-12 20:37 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From dje at gcc dot gnu dot org 2004-09-12 20:37 ------- On POWER4, the default processor, the latency of mulli relative to shifts and adds makes mulli a better choice than synthesizing the multiply by constant. When tuning for other PowerPC processors, such as POWER3, the synthesized sequence is generated. -- What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution| |INVALID http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17103 ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2004-09-12 20:37 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2004-08-19 14:59 [Bug other/17103] New: Opportunity to replace multiply with shift/add sequence gcc-bugzilla at gcc dot gnu dot org 2004-08-19 15:34 ` [Bug middle-end/17103] " pinskia at gcc dot gnu dot org 2004-08-19 15:46 ` [Bug target/17103] " falk at debian dot org 2004-09-12 20:37 ` dje at gcc dot gnu dot org
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