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From: "amonakov at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/39794] [4.4/4.5 Regression] Miscompile with -O2 -funroll-loops Date: Fri, 17 Apr 2009 21:55:00 -0000 [thread overview] Message-ID: <20090417215520.15794.qmail@sourceware.org> (raw) In-Reply-To: <bug-39794-13999@http.gcc.gnu.org/bugzilla/> ------- Comment #2 from amonakov at gcc dot gnu dot org 2009-04-17 21:55 ------- I attempted to investigate the miscompilation on the 4.4 branch. The problem seems to appear in dse2 pass. Basically, after encountering 313 dx:DI=ax:DI+0x4 187 {[di:DI+dx:DI]=[di:DI+dx:DI]<<0x1;clobber flags:CC;} ... 191 [di:DI+dx:DI+0x4]=cx:SI 314 dx:DI=ax:DI+0x8 200 {[di:DI+dx:DI]=[di:DI+dx:DI]<<0x1;clobber flags:CC;} and upon considering insn 200, dse2 decides to delete insn 191 and protect insn 187 (both are wrong, 200 depends on 191 and 187 is irrelevant): **scanning insn=200 mem: (plus:DI (reg/v/f:DI 5 di [orig:63 a ] [63]) (reg:DI 1 dx [orig:84 ivtmp.36 ] [84])) expanding: r5 into: NULL expanding: r1 into: (plus:DI (value:DI) (const_int 8 [0x8])) expanding value DI into: r0 expanding: r0 into: NULL after cselib_expand address: (plus:DI (plus:DI (reg/v/f:DI 5 di [orig:63 a ] [63]) (reg:DI 0 ax [orig:76 ivtmp.36 ] [76])) (const_int 8 [0x8])) after canon_rtx address: (plus:DI (plus:DI (reg/v/f:DI 5 di [orig:63 a ] [63]) (reg:DI 0 ax [orig:76 ivtmp.36 ] [76])) (const_int 8 [0x8])) varying cselib base=67 offset = 8 processing cselib load mem:(mem:SI (plus:DI (reg/v/f:DI 5 di [orig:63 a ] [63]) (reg:DI 1 dx [orig:84 ivtmp.36 ] [84])) [2 S4 A32]) processing cselib load against insn 191 processing cselib load against insn 187 removing from active insn=187 has store mem: (plus:DI (reg/v/f:DI 5 di [orig:63 a ] [63]) (reg:DI 1 dx [orig:84 ivtmp.36 ] [84])) expanding: r5 into: NULL expanding: r1 into: (plus:DI (value:DI) (const_int 8 [0x8])) expanding value DI into: r0 expanding: r0 into: NULL after cselib_expand address: (plus:DI (plus:DI (reg/v/f:DI 5 di [orig:63 a ] [63]) (reg:DI 0 ax [orig:76 ivtmp.36 ] [76])) (const_int 8 [0x8])) after canon_rtx address: (plus:DI (plus:DI (reg/v/f:DI 5 di [orig:63 a ] [63]) (reg:DI 0 ax [orig:76 ivtmp.36 ] [76])) (const_int 8 [0x8])) varying cselib base=67 offset = 8 processing cselib store [8..12) trying store in insn=191 gid=-1[8..12) Locally deleting insn 191 deferring deletion of insn with uid = 191. mems_found = 1, cannot_delete = false I wonder how dse2 is supposed to notice that insn 314 changes DX. E.g. when checking rhs of insn 200 ([di+dx]) against lhs of insn 191 ([di+dx+4] for different dx) in check_mem_read_rtx it calls canon_true_dependence (from dse.c:2224) for [di+dx] and [di+dx+4] which returns false. However, these references clearly conflict. Maybe a stupid question, but shouldn't this canon_true_dependence call receive canonicalized MEMs from 'base' and 'store_info->cse_base'? -- amonakov at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |amonakov at gmail dot com, | |amonakov at gcc dot gnu dot | |org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39794
next prev parent reply other threads:[~2009-04-17 21:55 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2009-04-17 9:58 [Bug middle-end/39794] New: " abel at gcc dot gnu dot org 2009-04-17 10:27 ` [Bug middle-end/39794] [4.4/4.5 Regression] " amonakov at gcc dot gnu dot org 2009-04-17 10:35 ` rguenth at gcc dot gnu dot org 2009-04-17 11:43 ` jakub at gcc dot gnu dot org 2009-04-17 12:19 ` rguenth at gcc dot gnu dot org 2009-04-17 21:55 ` amonakov at gcc dot gnu dot org [this message] 2009-04-17 22:06 ` rguenth at gcc dot gnu dot org 2009-04-20 15:48 ` bonzini at gnu dot org 2009-04-20 17:46 ` jakub at gcc dot gnu dot org 2009-04-21 16:02 ` jakub at gcc dot gnu dot org 2009-04-21 17:23 ` jakub at gcc dot gnu dot org 2009-04-22 13:41 ` rguenth at gcc dot gnu dot org 2009-04-22 16:55 ` alexey dot zaytsev at gmail dot com 2009-04-22 16:58 ` alexey dot zaytsev at gmail dot com 2009-04-23 14:37 ` bonzini at gnu dot org 2009-04-24 6:58 ` [Bug rtl-optimization/39794] " jakub at gcc dot gnu dot org 2009-04-27 11:55 ` jakub at gcc dot gnu dot org 2009-04-27 12:49 ` jakub at gcc dot gnu dot org
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