[TESTCASE] Minimized testcase for AltiVec segfault

[Daniel Egger <degger at fhm dot edu>]

Hija,

the attached testcase will segfault on powerpc-linux when compiled with
-O0.

egger@sonja:~$ /opt/gcc/bin/gcc -da -maltivec -save-temps -O0 -mregnames
test2.c -o test2 -Wall
test2.c: In function `do_something':
test2.c:7: warning: unused variable `zeros'
egger@sonja:~$ ./test2 
Segmentation fault

Works with -O2:
egger@sonja:~$ /opt/gcc/bin/gcc -da -maltivec -save-temps -O2 -mregnames
test2.c -o test2 -Wall
test2.c: In function `do_something':
test2.c:7: warning: unused variable `zeros'
egger@sonja:~$ ./test2 
egger@sonja:~$ 

do_something:
        stwu %r1,-96(%r1)
        stw %r31,92(%r1)
        mr %r31,%r1
        stw %r3,8(%r31)
        lis %r9,.LC0@ha
        la %r9,.LC0@l(%r9)
        lvx %v0,0,%r9
        li %r0,32
        stvx %v0,%r31,%r0
        li %r0,32
        lvx %v0,%r31,%r0
        li %r0,16
        stvx %v0,%r31,%r0
        lwz %r0,8(%r31)
        stw %r0,48(%r31)
        lwz %r9,48(%r31)
        lvx %v0,0,%r9       <--- This is an offending line.
        li %r0,56
        stvx %v0,%r31,%r0
        lwz %r9,48(%r31)
        li %r0,56
        lvx %v0,%r31,%r0
        stvx %v0,0,%r9      <--- This is an offending line.
        lwz %r11,0(%r1)
        lwz %r31,-4(%r11)
        mr %r1,%r11
        blr

One problem with this marked lines is that there is no direct vector
load or vector store with the second argument being 0 to directly
address the memory at the pointer in the third argument which gcc seem
to assume exists.

Even worse for the store is that %r9 points to 0 and %r0 is 56 (while
it is probably assumed to be ignored) which means that address
generation is wrong anyway even if the syntax was right.

-- 
Servus,
       Daniel
#include <altivec.h>
#include <malloc.h>

void
do_something (signed short *mem)
{
  const vector signed short zeros = (vector signed short) {0,0,0,0,0,0,0};
  vector signed short *vec;
  vector signed short v1[1];

  vec = (vector signed short *) mem;
  
  v1[0] = vec[0];
  vec[0] = v1[0];
}

int
main (void)
{
  void *mem = memalign (128, 16);
  
  if (mem)
  {
    do_something (mem);
    free (mem);
  }
 
  return 0;
}