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optimization/6080: incorrect loop optimizations
- From: anders dot blomdell at control dot lth dot se
- To: gcc-gnats at gcc dot gnu dot org
- Date: 28 Mar 2002 10:46:59 -0000
- Subject: optimization/6080: incorrect loop optimizations
- Reply-to: anders dot blomdell at control dot lth dot se
>Number: 6080
>Category: optimization
>Synopsis: incorrect loop optimizations
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Thu Mar 28 02:56:01 PST 2002
>Closed-Date:
>Last-Modified:
>Originator: Anders Blomdell <anders.blomdell@control.lth.se>
>Release: 3.0.4
>Organization:
>Environment:
System: Linux aljazari 2.4.13-KURT #2 Thu Nov 8 10:49:33 CET 2001 i686 unknown
Architecture: i686
<machine, os, target, libraries (multiple lines)>
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: m68k-unknown-elf
configured with: ../../../gcc-3.0.4/configure --prefix=/usr/local/packages/cross
/m68k-elf --target=m68k-elf --with-newlib : (reconfigured) ../../../gcc-3.0.4/co
nfigure --prefix=/usr/local/packages/cross/m68k-elf --target=m68k-elf --with-new
lib : (reconfigured) ../../../gcc-3.0.4/configure --with-gcc-version-trigger=/wo
rk/aljazari2/andersb/gnu/gcc-3.0.4/gcc/version.c --host=i686-pc-linux-gnu --pref
ix=/usr/local/packages/cross/m68k-elf --target=m68k-elf --with-newlib --enable-c
hecking=misc,tree,rtl,gc,gcac
>Description:
gcc -O5 makes incorrect loop optimizations on the following code:
// case A: h get called infinite times
static void ug0(unsigned int count)
{
while (count > 0) { ug0(0); h(); count--; }
}
void uf0() { ug0(1000); }
// case B: h gets called only once
static void sg0(int count)
{
while (count > 0) { sg0(0); h(); count--; }
}
void sf0() { sg0(1000); }
This is the m68k code that gets produced (ppc code exhibits same problem...)
80000128 <uf0>:
80000128: 4e56 0000 linkw %fp,#0
8000012c: 42a7 clrl %sp@-
8000012e: 6120 bsrs 80000150 <ug0>
80000130: 61ff ffff ffda bsrl 8000010c <h>
80000136: 588f addql #4,%sp
80000138: 60f2 bras 8000012c <uf0+0x4>
8000013a: 4e71 nop
8000013c <sf0>:
8000013c: 4e56 0000 linkw %fp,#0
80000140: 42a7 clrl %sp@-
80000142: 6130 bsrs 80000174 <sg0>
80000144: 61ff ffff ffc6 bsrl 8000010c <h>
8000014a: 588f addql #4,%sp
8000014c: 4e5e unlk %fp
8000014e: 4e75 rts
>How-To-Repeat:
Compile the testprogram with -O5
>Fix:
Turn off optimization
>Release-Note:
>Audit-Trail:
>Unformatted: