public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "gjl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/49687] New: AVR: Missed optimization for widening MUL Date: Sat, 09 Jul 2011 09:36:00 -0000 [thread overview] Message-ID: <bug-49687-4@http.gcc.gnu.org/bugzilla/> (raw) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49687 Summary: AVR: Missed optimization for widening MUL Product: gcc Version: 4.6.1 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: target AssignedTo: unassigned@gcc.gnu.org ReportedBy: gjl@gcc.gnu.org Target: avr With avr-gcc 4.6.1 and -Os -mmcu=atmega88 -S -dp int mul8_55 (char x) { return x * 55; } gets compiled to mul8_55: ldi r25,lo8(55) ; 7 *movqi/2 [length = 1] muls r24,r25 ; 8 mulqihi3 [length = 3] movw r24,r0 clr r1 ret ; 26 return [length = 1] which is fine. If the constant is 126, however, the result is bloated and might be related to PR36467, i.e. MUL* is better than shift. mul8_126: clr r25 ; 7 extendqihi2/1 [length = 3] sbrc r24,7 com r25 movw r18,r24 ; 28 *movhi/1 [length = 1] lsl r18 ; 33 *ashlhi3_const/2 [length = 2] rol r19 lsr r25 ; 34 *ashlhi3_const/5 [length = 5] mov r25,r24 clr r24 ror r25 ror r24 sub r24,r18 ; 12 subhi3/1 [length = 2] sbc r25,r19 ret ; 31 return [length = 1] If the constant is 155, a MUL is invented, but a widening MUL would be smarter: mul8_155: mov r20,r24 ; 6 extendqihi2/2 [length = 4] clr r21 sbrc r20,7 com r21 ldi r18,lo8(155) ; 7 *movhi/4 [length = 2] ldi r19,hi8(155) mul r20,r18 ; 8 *mulhi3_enh [length = 7] movw r24,r0 mul r20,r19 add r25,r0 mul r21,r18 add r25,r0 clr r1 ret ; 26 return [length = 1]
next reply other threads:[~2011-07-09 9:36 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-07-09 9:36 gjl at gcc dot gnu.org [this message] 2011-07-09 9:37 ` [Bug target/49687] " gjl at gcc dot gnu.org 2011-07-09 9:39 ` gjl at gcc dot gnu.org 2011-07-14 18:43 ` eric.weddington at atmel dot com 2011-07-14 18:45 ` [Bug target/49687] [4.6 Regression][avr] " eric.weddington at atmel dot com 2011-07-20 17:25 ` gjl at gcc dot gnu.org 2011-07-28 8:03 ` gjl at gcc dot gnu.org 2011-07-29 11:28 ` gjl at gcc dot gnu.org 2011-07-29 11:50 ` gjl at gcc dot gnu.org 2011-08-11 7:51 ` gjl at gcc dot gnu.org 2011-08-11 21:45 ` gjl at gcc dot gnu.org 2011-09-09 18:09 ` gjl at gcc dot gnu.org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=bug-49687-4@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).