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From: Falk Hueffner <falk.hueffner@student.uni-tuebingen.de> To: gcc-gnats@gcc.gnu.org Subject: optimization/8883: Alpha: regalloc too eager to use FP regs on EV6 Date: Mon, 09 Dec 2002 14:46:00 -0000 [thread overview] Message-ID: <E18LWai-0004uk-00@juist> (raw) >Number: 8883 >Category: optimization >Synopsis: Alpha: regalloc too eager to use FP regs on EV6 >Confidential: no >Severity: serious >Priority: medium >Responsible: unassigned >State: open >Class: pessimizes-code >Submitter-Id: net >Arrival-Date: Mon Dec 09 14:46:00 PST 2002 >Closed-Date: >Last-Modified: >Originator: Falk Hueffner >Release: 3.3 20021102 (experimental) >Organization: >Environment: System: Linux juist 2.4.20-rc1 #1 Sun Nov 10 15:01:35 CET 2002 alpha unknown unknown GNU/Linux Architecture: alpha host: alphaev68-unknown-linux-gnu build: alphaev68-unknown-linux-gnu target: alphaev68-unknown-linux-gnu configured with: ../configure --disable-nls --enable-languages=c++ >Description: % cat med.c typedef unsigned long uint64_t; uint64_t median(uint64_t a, uint64_t b, uint64_t c) { return (a < b != b >= c) ? b : ((a < c != c > b) ? c : a); } % gcc -c -mcpu=ev6 -O3 med.c && objdump -d med.o 0000000000000000 <median>: 0: a4 03 12 42 cmpult a0,a2,t3 4: a1 03 32 42 cmpult a1,a2,t0 8: a3 07 51 42 cmpule a2,a1,t2 c: a6 07 30 42 cmpule a1,a0,t5 10: 05 08 81 44 xor t3,t0,t4 14: 02 08 c3 44 xor t5,t2,t1 18: 92 04 b0 44 cmoveq t4,a0,a2 1c: 8a 04 5f 52 itoft a2,$f10 20: 01 00 40 f4 bne t1,28 <median+0x28> 24: 8a 04 3f 52 itoft a1,$f10 28: 00 0e 5f 71 ftoit $f10,v0 2c: 01 80 fa 6b ret itoft has a latency of 4, and ftoi a latency of 3, so they should really only be used if it cannot be avoided. (Also, the branch can be replaced with a cmov, but that's probably more difficult to fix.) This problem does not occur with -mcpu=ev5, or with -fnew-ra. >How-To-Repeat: >Fix: >Release-Note: >Audit-Trail: >Unformatted:
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