[Bug c++/19263] New: [g++-3.4.3 regression]: wrong-code: explicit inicialization of v8qi miscompiled

["smelkov at mph1 dot phys dot spbu dot ru" <gcc-bugzilla at gcc dot gnu dot org>]

In the following code sample the line 
v8qi val8 = {v,v,v,v,v,v,v,v}; 
 
is miscompiled to smth like 
v8qi val8 = {0,0,0,0,0,0,0,0}; 
 
 
---v8qi-init.cpp--- 
typedef int v8qi __attribute__ ((mode(V8QI))); 
 
static unsigned char S[8]; 
 
void do_subs(unsigned char v) 
{ 
    v8qi  val8 = {v,v,v,v,v,v,v,v}; 
    v8qi* s = (v8qi*)&S[0]; 
 
    *s = __builtin_ia32_psubusb(*s, val8); 
} 
 
 
int main() 
{ 
    int i; 
 
    for (i=0;i<8;++i) 
        S[i] = 0x55; 
 
 
    do_subs(0x54); 
 
    for (i=0;i<8;++i) 
        if (S[i] != 0x01) 
            return 1; 
 
 
    return 0; 
} 
--- 
 
[kirr@tugrik gcc-v8qi-bug]$ g++ -v 
Reading specs from /usr/local/gcc-3.4.3-nocheck-native/lib/gcc/i686-pc-linux-gnu/3.4.3/specs 
Configured with: ../gcc-3.4.3/configure --prefix=/usr/local/gcc-3.4.3-nocheck-native 
--with-gnu-as --with-gnu-ld --enable-threads=posix --with-arch=pentium3 
--with-tune=pentium4 --enable-__cxa_atexit --enable-languages=c,c++,java,f77,ada 
--disable-checking --disable-nls 
Thread model: posix 
gcc version 3.4.3 
 
[kirr@tugrik gcc-v8qi-bug]$ g++ -g -Wall -march=i686 -mmmx v8qi-init.cpp  
[kirr@tugrik gcc-v8qi-bug]$ ./a.out  
[kirr@tugrik gcc-v8qi-bug]$ echo $? 
1 
 
--- 
with g++-3.4.2 it is ok, so it is a regression. 
please also note, that with gcc-3.4.3 it is also ok, so it is g++ specific (???) 
 
here are assembly parts: 
 
---g++-3.4.3--- 
void do_subs(unsigned char v) 
{ 
 8048374:       55                      push   %ebp 
 8048375:       89 e5                   mov    %esp,%ebp 
 8048377:       83 ec 18                sub    $0x18,%esp 
 804837a:       8b 45 08                mov    0x8(%ebp),%eax 
 804837d:       88 45 ff                mov    %al,0xffffffff(%ebp) 
    v8qi  val8 = {v,v,v,v,v,v,v,v}; 
 8048380:       0f ef c0                pxor   %mm0,%mm0 
 8048383:       0f 7f 45 f0             movq   %mm0,0xfffffff0(%ebp) 
    v8qi* s = (v8qi*)&S[0]; 
 8048387:       c7 45 ec f4 95 04 08    movl   $0x80495f4,0xffffffec(%ebp) 
  
    *s = __builtin_ia32_psubusb(*s, val8); 
 804838e:       8b 55 ec                mov    0xffffffec(%ebp),%edx 
 8048391:       8b 45 ec                mov    0xffffffec(%ebp),%eax 
 8048394:       0f 6f 00                movq   (%eax),%mm0 
 8048397:       0f d8 45 f0             psubusb 0xfffffff0(%ebp),%mm0 
 804839b:       0f 7f 02                movq   %mm0,(%edx) 
} 
 804839e:       c9                      leave   
 804839f:       c3                      ret 
--- 
 
note: pxor %mm0,%mm0 after "val8=..." 
 
---g++-3.4.2--- 
void do_subs(unsigned char v) 
{ 
 8048374:       55                      push   %ebp 
 8048375:       89 e5                   mov    %esp,%ebp 
 8048377:       83 ec 18                sub    $0x18,%esp 
 804837a:       8b 45 08                mov    0x8(%ebp),%eax 
 804837d:       88 45 ff                mov    %al,0xffffffff(%ebp) 
    v8qi  val8 = {v,v,v,v,v,v,v,v}; 
 8048380:       0f b6 45 ff             movzbl 0xffffffff(%ebp),%eax 
 8048384:       88 45 f0                mov    %al,0xfffffff0(%ebp) 
 8048387:       0f b6 45 ff             movzbl 0xffffffff(%ebp),%eax 
 804838b:       88 45 f1                mov    %al,0xfffffff1(%ebp) 
 804838e:       0f b6 45 ff             movzbl 0xffffffff(%ebp),%eax 
 8048392:       88 45 f2                mov    %al,0xfffffff2(%ebp) 
 8048395:       0f b6 45 ff             movzbl 0xffffffff(%ebp),%eax 
 8048399:       88 45 f3                mov    %al,0xfffffff3(%ebp) 
 804839c:       0f b6 45 ff             movzbl 0xffffffff(%ebp),%eax 
 80483a0:       88 45 f4                mov    %al,0xfffffff4(%ebp) 
 80483a3:       0f b6 45 ff             movzbl 0xffffffff(%ebp),%eax 
 80483a7:       88 45 f5                mov    %al,0xfffffff5(%ebp) 
 80483aa:       0f b6 45 ff             movzbl 0xffffffff(%ebp),%eax 
 80483ae:       88 45 f6                mov    %al,0xfffffff6(%ebp) 
 80483b1:       0f b6 45 ff             movzbl 0xffffffff(%ebp),%eax 
 80483b5:       88 45 f7                mov    %al,0xfffffff7(%ebp) 
    v8qi* s = (v8qi*)&S[0]; 
 80483b8:       c7 45 ec 24 96 04 08    movl   $0x8049624,0xffffffec(%ebp) 
 
    *s = __builtin_ia32_psubusb(*s, val8); 
 80483bf:       8b 55 ec                mov    0xffffffec(%ebp),%edx 
 80483c2:       8b 45 ec                mov    0xffffffec(%ebp),%eax 
 80483c5:       0f 6f 00                movq   (%eax),%mm0 
 80483c8:       0f d8 45 f0             psubusb 0xfffffff0(%ebp),%mm0 
 80483cc:       0f 7f 02                movq   %mm0,(%edx) 
} 
 80483cf:       c9                      leave 
 80483d0:       c3                      ret 
 80483d1:       90                      nop 
---

-- 
           Summary: [g++-3.4.3 regression]: wrong-code: explicit
                    inicialization of v8qi miscompiled
           Product: gcc
           Version: 3.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: smelkov at mph1 dot phys dot spbu dot ru
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19263