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* [Bug tree-optimization/19803] New: __builtin_expect doesnt modify branch prediction for power4 target @ 2005-02-07 15:28 anton at samba dot org 2005-02-07 17:21 ` [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 pinskia at gcc dot gnu dot org ` (5 more replies) 0 siblings, 6 replies; 7+ messages in thread From: anton at samba dot org @ 2005-02-07 15:28 UTC (permalink / raw) To: gcc-bugs gcc version 4.0.0 20050203 (experimental) The following code snippet shows how branch prediction isnt used even when specifying builtin_expect. flags used: -O2 -mcpu=power4 #if 1 #define likely(x) __builtin_expect(!!(x), 1) #else #define likely(x) x #endif int i; void foo(void) { while (likely(i--)) { bar(); } } ... b .L2 .p2align 4,,15 .L3: bl bar nop .L2: lwz 9,0(31) addi 9,9,-1 extsw 9,9 cmpwi 7,9,-1 stw 9,0(31) bne 7,.L3 -- Summary: __builtin_expect doesnt modify branch prediction for power4 target Product: gcc Version: 4.0.0 Status: UNCONFIRMED Severity: enhancement Priority: P2 Component: tree-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: anton at samba dot org CC: gcc-bugs at gcc dot gnu dot org GCC target triplet: powerpc64-unknown-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19803 ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 2005-02-07 15:28 [Bug tree-optimization/19803] New: __builtin_expect doesnt modify branch prediction for power4 target anton at samba dot org @ 2005-02-07 17:21 ` pinskia at gcc dot gnu dot org 2005-02-07 17:21 ` [Bug tree-optimization/19803] __builtin_expect doesnt modify branch prediction for power4 target amodra at bigpond dot net dot au ` (4 subsequent siblings) 5 siblings, 0 replies; 7+ messages in thread From: pinskia at gcc dot gnu dot org @ 2005-02-07 17:21 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From pinskia at gcc dot gnu dot org 2005-02-07 03:39 ------- (In reply to comment #1) > builtin_expect uses PROB_VERY_LIKELY. > > But powerpc64 only emits branch prediction hints when at 2% / 98%. See > rs6000.c:output_cbranch This is a target problem as mentioned above. Hmm, I thought there was a patch floating around to fix this but I could be wrong. Also note this changed back in 2002 for power4: <http://gcc.gnu.org/ml/gcc-patches/2002-08/msg00149.html> so in a way it could be considered a regression. It also effects power5 also (and ppc970). -- What |Removed |Added ---------------------------------------------------------------------------- CC| |pinskia at gcc dot gnu dot | |org Component|tree-optimization |target GCC target triplet|powerpc64-unknown-linux-gnu |powerpc*-*-* Summary|__builtin_expect doesnt |__builtin_expect does not |modify branch prediction for|modify branch prediction for |power4 target |power4/5 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19803 ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/19803] __builtin_expect doesnt modify branch prediction for power4 target 2005-02-07 15:28 [Bug tree-optimization/19803] New: __builtin_expect doesnt modify branch prediction for power4 target anton at samba dot org 2005-02-07 17:21 ` [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 pinskia at gcc dot gnu dot org @ 2005-02-07 17:21 ` amodra at bigpond dot net dot au 2005-02-07 17:25 ` [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 amodra at bigpond dot net dot au ` (3 subsequent siblings) 5 siblings, 0 replies; 7+ messages in thread From: amodra at bigpond dot net dot au @ 2005-02-07 17:21 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From amodra at bigpond dot net dot au 2005-02-07 03:28 ------- builtin_expect uses PROB_VERY_LIKELY. >From predict.c #define PROB_VERY_UNLIKELY (REG_BR_PROB_BASE / 10 - 1) #define PROB_EVEN (REG_BR_PROB_BASE / 2) #define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY) #define PROB_ALWAYS (REG_BR_PROB_BASE) In other words, builtin_expect is using 10% / 90% But powerpc64 only emits branch prediction hints when at 2% / 98%. See rs6000.c:output_cbranch -- What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Ever Confirmed| |1 Last reconfirmed|0000-00-00 00:00:00 |2005-02-07 03:28:18 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19803 ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 2005-02-07 15:28 [Bug tree-optimization/19803] New: __builtin_expect doesnt modify branch prediction for power4 target anton at samba dot org 2005-02-07 17:21 ` [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 pinskia at gcc dot gnu dot org 2005-02-07 17:21 ` [Bug tree-optimization/19803] __builtin_expect doesnt modify branch prediction for power4 target amodra at bigpond dot net dot au @ 2005-02-07 17:25 ` amodra at bigpond dot net dot au 2005-02-08 9:18 ` cvs-commit at gcc dot gnu dot org ` (2 subsequent siblings) 5 siblings, 0 replies; 7+ messages in thread From: amodra at bigpond dot net dot au @ 2005-02-07 17:25 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From amodra at bigpond dot net dot au 2005-02-07 04:47 ------- patch http://gcc.gnu.org/ml/gcc-patches/2005-02/msg00225.html -- What |Removed |Added ---------------------------------------------------------------------------- Severity|enhancement |normal Keywords| |patch http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19803 ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 2005-02-07 15:28 [Bug tree-optimization/19803] New: __builtin_expect doesnt modify branch prediction for power4 target anton at samba dot org ` (2 preceding siblings ...) 2005-02-07 17:25 ` [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 amodra at bigpond dot net dot au @ 2005-02-08 9:18 ` cvs-commit at gcc dot gnu dot org 2005-02-08 9:19 ` cvs-commit at gcc dot gnu dot org 2005-02-08 9:25 ` amodra at bigpond dot net dot au 5 siblings, 0 replies; 7+ messages in thread From: cvs-commit at gcc dot gnu dot org @ 2005-02-08 9:18 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From cvs-commit at gcc dot gnu dot org 2005-02-07 21:12 ------- Subject: Bug 19803 CVSROOT: /cvs/gcc Module name: gcc Changes by: amodra@gcc.gnu.org 2005-02-07 21:11:45 Modified files: gcc : ChangeLog predict.c Log message: PR target/19803 * predict.c (PROB_VERY_UNLIKELY): Use 1% instead of 10%. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.7414&r2=2.7415 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/predict.c.diff?cvsroot=gcc&r1=1.137&r2=1.138 -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19803 ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 2005-02-07 15:28 [Bug tree-optimization/19803] New: __builtin_expect doesnt modify branch prediction for power4 target anton at samba dot org ` (3 preceding siblings ...) 2005-02-08 9:18 ` cvs-commit at gcc dot gnu dot org @ 2005-02-08 9:19 ` cvs-commit at gcc dot gnu dot org 2005-02-08 9:25 ` amodra at bigpond dot net dot au 5 siblings, 0 replies; 7+ messages in thread From: cvs-commit at gcc dot gnu dot org @ 2005-02-08 9:19 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From cvs-commit at gcc dot gnu dot org 2005-02-07 21:18 ------- Subject: Bug 19803 CVSROOT: /cvs/gcc Module name: gcc Branch: gcc-3_4-branch Changes by: amodra@gcc.gnu.org 2005-02-07 21:18:33 Modified files: gcc : ChangeLog predict.c Log message: PR target/19803 * predict.c (PROB_VERY_UNLIKELY): Use 1% instead of 10%. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_4-branch&r1=2.2326.2.794&r2=2.2326.2.795 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/predict.c.diff?cvsroot=gcc&only_with_tag=gcc-3_4-branch&r1=1.98&r2=1.98.2.1 -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19803 ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 2005-02-07 15:28 [Bug tree-optimization/19803] New: __builtin_expect doesnt modify branch prediction for power4 target anton at samba dot org ` (4 preceding siblings ...) 2005-02-08 9:19 ` cvs-commit at gcc dot gnu dot org @ 2005-02-08 9:25 ` amodra at bigpond dot net dot au 5 siblings, 0 replies; 7+ messages in thread From: amodra at bigpond dot net dot au @ 2005-02-08 9:25 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From amodra at bigpond dot net dot au 2005-02-07 21:23 ------- Fixed. -- What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution| |FIXED Target Milestone|--- |4.0.0 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19803 ^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2005-02-07 21:24 UTC | newest] Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2005-02-07 15:28 [Bug tree-optimization/19803] New: __builtin_expect doesnt modify branch prediction for power4 target anton at samba dot org 2005-02-07 17:21 ` [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 pinskia at gcc dot gnu dot org 2005-02-07 17:21 ` [Bug tree-optimization/19803] __builtin_expect doesnt modify branch prediction for power4 target amodra at bigpond dot net dot au 2005-02-07 17:25 ` [Bug target/19803] __builtin_expect does not modify branch prediction for power4/5 amodra at bigpond dot net dot au 2005-02-08 9:18 ` cvs-commit at gcc dot gnu dot org 2005-02-08 9:19 ` cvs-commit at gcc dot gnu dot org 2005-02-08 9:25 ` amodra at bigpond dot net dot au
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