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From: bjh21@netbsd.org To: gcc-gnats@gcc.gnu.org Subject: optimization/4733: Incorrect code when aliasing double and struct on ARM -O2 Date: Mon, 29 Oct 2001 09:26:00 -0000 [thread overview] Message-ID: <E15yG0g-00054n-00@wraith.csi.cam.ac.uk> (raw) >Number: 4733 >Category: optimization >Synopsis: Incorrect code when aliasing double and struct on ARM -O2 >Confidential: no >Severity: serious >Priority: medium >Responsible: unassigned >State: open >Class: wrong-code >Submitter-Id: net >Arrival-Date: Mon Oct 29 09:26:00 PST 2001 >Closed-Date: >Last-Modified: >Originator: Ben Harris >Release: 3.1 20011023 (experimental) >Organization: The NetBSD Project >Environment: System: Linux wraith 2.4.12 #13 Mon Oct 29 11:21:47 GMT 2001 i686 unknown Architecture: i686 host: i686-pc-linux-gnu build: i686-pc-linux-gnu target: arm-unknown-elf configured with: ./configure --target=arm-unknown-elf >Description: Compiling the code below with -O2 generates, at the start of the function: sub sp, sp, #8 mov r2, #2032 ldrh r3, [sp, #6] @ movhi add r2, r2, #15 and r3, r2, r3, lsr #4 cmp r3, r2 stmia sp, {r0-r1} As far as I can see, this allocates eight bytes of stack, loads from it (ldrh), messes around a bit and then stores the value it was expecting to load (stmia). Obviously the stmia shouldn't have been moved to after the ldrh. This problem also exists in GCC 3.0.1 and the NetBSD version of GCC 2.95.3 (where I first found it). >How-To-Repeat: use "./cc1 -O2" typedef unsigned int u_int; struct ieee_double { u_int dbl_fracl; u_int dbl_frach:20; u_int dbl_exp:11; u_int dbl_sign:1; }; int isinf (d) double d; { register struct ieee_double *p = (struct ieee_double *)(void *)&d; return (p->dbl_exp == 2047 && (p->dbl_frach == 0 && p->dbl_fracl == 0)); } >Fix: -fno-schedule-insns -fno-schedule-insns2 causes the problem to go away. >Release-Note: >Audit-Trail: >Unformatted:
next reply other threads:[~2001-10-29 9:26 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2001-10-29 9:26 bjh21 [this message] 2001-10-29 9:56 Richard Earnshaw 2001-10-29 10:16 Ben Harris 2002-02-04 13:29 toon
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