Bug#1130962: m68k: Miscompilation at -O2

Camm Maguire <[email protected]>
Newsgroups gmane.linux.debian.devel.gcc
Message-ID <87y0jr53gh.fsf__42913.8201217697$1773667188$gmane$org@glory.maguirefamily.org> 
Package: gcc-15
X-Debbugs-Cc: [email protected]
Version: 15.2.0-13
Severity: important
Tags: upstream

Dear Maintainer,

At -O2 gcc miscompiles the following snippet of C code

	V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});

as the gdb transcript below demonstrates.  In particular, the starting
address of _y, which should be V2048, is offset by 4 bytes.  The
problem vanishes at -O1.

=============================================================================
(gdb) b 17163
Breakpoint 4 at 0x23b04f2: file pcl_gcl/gcl_pcl_dfun.c, line 17163.
(gdb) c
Continuing.

Breakpoint 4, LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun (V2046=0xe44078, 
    V2047=0x1888b10) at pcl_gcl/gcl_pcl_dfun.c:17163
17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b04f2 <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+514>:	moveal %a3@,%a0
(gdb) p/x fcall.valp
$35 = 0x0
(gdb) p V2048
$36 = -1073746348
(gdb) p/x V2048
$37 = 0xbfffee54
(gdb) p *(ul *)0xbfffee54@4
$38 = {0, 2027206421, 3221221104, 819826}
(gdb) p/x *(ul *)0xbfffee54@4
$39 = {0x0, 0x78d4b715, 0xbfffeef0, 0xc8272}
(gdb) p vs_top-vs_base
$40 = 3
(gdb) i reg a3
a3             0x79f114            0x79f114
(gdb) p vs_base
$41 = (object *) 0x79f114
(gdb) si
17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b04f4 <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+516>:	addql #8,%sp
(gdb) i reg sp
sp             0xbfffed30          0xbfffed30
(gdb) si
0x023b04f6	17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b04f6 <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+518>:	tstl %a4
(gdb) i reg a4
a4             0xbfffee54          0xbfffee54
(gdb) si
0x023b04f8	17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b04f8 <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+520>:	
    beqs 0x23b052c <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+572>
(gdb) si
0x023b04fa	17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b04fa <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+522>:	cmpl %d3,%d2
(gdb) i reg d3
d3             0x79f120            7991584
(gdb) i reg d2
d2             0x79f118            7991576
(gdb) p _x
$42 = <optimized out>
(gdb) p vs_top
$43 = (object *) 0x79f120
(gdb) si
0x023b04fc	17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b04fc <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+524>:	
    bccw 0x23b08de <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+1518>
(gdb) 
0x023b0500	17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b0500 <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+528>:	moveal %d2,%a1
(gdb) i reg d2
d2             0x79f118            7991576
(gdb) i reg a1
a1             0x4200000           0x4200000
(gdb) si
0x023b0502	17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b0502 <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+530>:	movel %a4,%d0
(gdb) i reg a4
a4             0xbfffee54          0xbfffee54
(gdb) i reg d0
d0             0x4355d20           70606112
(gdb) si
0x023b0504	17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b0504 <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+532>:	subql #4,%d0
(gdb) i reg d0
d0             0xbfffee54          -1073746348
(gdb) si
0x023b0506	17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b0506 <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+534>:	subl %a3,%d0
(gdb) i reg d0
d0             0xbfffee50          -1073746352
(gdb) i reg a3
a3             0x79f114            0x79f114
(gdb) si
0x023b0508	17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b0508 <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+536>:	
    movel %a1@+,%a1@(0,%d0:l)
(gdb) i reg d0
d0             0xbf85fd3c          -1081737924
(gdb) i reg a1
a1             0x79f118            0x79f118
(gdb) i reg d0
d0             0xbf85fd3c          -1081737924
(gdb) p *(ul *)0xbfffee54@4
$44 = {0, 2027206421, 3221221104, 819826}
(gdb) p/s *(ul *)0xbfffee54@4
$45 = {0, 2027206421, 3221221104, 819826}
(gdb) p/x *(ul *)0xbfffee54@4
$46 = {0x0, 0x78d4b715, 0xbfffeef0, 0xc8272}
(gdb) p *(ul *)0x79f118
$47 = 7704728
(gdb) p/x *(ul *)0x79f118
$48 = 0x759098
(gdb) si
0x023b050c	17163		V2083= ({register object _z=vs_base[0];register object *_x=vs_base+1,*_y=(object *)V2048;if (!_y) vs_top=base; else {for(;_x<vs_top;) *_y++=*_x++;if (_x>vs_top) _y--;vs_top=_y;}_z;});
1: x/i $pc
=> 0x23b050c <LI148__MAKE_FINAL_ACCESSOR_DFUN__pcl_dfun+540>:	cmpal %d3,%a1
(gdb) p/x *(ul *)0xbfffee54@4
$49 = {0x0, 0x759098, 0xbfffeef0, 0xc8272}
(gdb) q
=============================================================================

-- System Information:
Debian Release: forky/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: m68k

Kernel: Linux 6.12.48+deb13-amd64 (SMP w/8 CPU threads; PREEMPT)
Kernel taint flags: TAINT_WARN
Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: unable to detect

Versions of packages gcc-15 depends on:
ii  binutils               2.46-2
ii  cpp-15                 15.2.0-13
ii  gcc-15-base            15.2.0-13
ii  gcc-15-m68k-linux-gnu  15.2.0-13

Versions of packages gcc-15 recommends:
ii  libc6-dev  2.42-5

Versions of packages gcc-15 suggests:
pn  gcc-15-doc      <none>
pn  gcc-15-locales  <none>

-- no debconf information
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