On 25 July 2011 12:39, Richard Guenther <richard.guent...@gmail.com> wrote: > On Mon, Jul 25, 2011 at 11:10 AM, Ulrich Weigand <uweig...@de.ibm.com> wrote: >> Richard Guenther wrote: >>> On Sun, Jul 24, 2011 at 2:02 PM, Ira Rosen <ira.ro...@linaro.org> wrote: >>> > On 21 July 2011 15:19, Ira Rosen <ira.ro...@linaro.org> wrote: >>> >> I reproduced the failure. It occurs without Richard's >>> >> (http://gcc.gnu.org/ml/gcc-patches/2011-07/msg01022.html) and this >>> >> patches too. Obviously the vectorized loop is executed, but at the >>> >> moment I don't understand why. I'll have a better look on Sunday. >>> > >>> > Actually it doesn't choose the vectorized code. But the scalar version >>> > gets optimized in a harmful way for SPU, AFAIU. >>> > Here is the scalar loop after vrp2 >>> > >>> > <bb 8>: >>> > # ivtmp.42_50 = PHI <ivtmp.42_59(3), ivtmp.42_45(10)> >>> > D.4593_42 = (void *) ivtmp.53_32; >>> > D.4520_33 = MEM[base: D.4593_42, offset: 0B]; >>> > D.4521_34 = D.4520_33 + 1; >>> > MEM[symbol: a, index: ivtmp.42_50, offset: 0B] = D.4521_34; >>> > ivtmp.42_45 = ivtmp.42_50 + 4; >>> > if (ivtmp.42_45 != 16) >>> > goto <bb 10>; >>> > else >>> > goto <bb 5>; >>> > >>> > and the load is changed by dom2 to: >>> > >>> > <bb 4>: >>> > ... >>> > D.4520_33 = MEM[base: vect_pa.9_19, offset: 0B]; >>> > ... >>> > >>> > where vector(4) int * vect_pa.9; >>> > >>> > And the scalar loop has no rotate for that load: >>> >>> Hum. This smells like we are hiding sth from the tree optimizers? >> >> Well, the back-end assumes a pointer to vector type is always >> naturally aligned, and therefore the data it points to can be >> accessed via a simple load, with no extra rotate needed. > > I can't see any use of VECTOR_TYPE in config/spu/, and assuming > anything about alignment just because of the kind of the pointer > is bogus - the scalar code does a scalar read using that pointer. > So the backend better should look at the memory operation, not > at the pointer type. That said, I can't find any code that looks > suspicious in the spu backend. > >> It seems what happened here is that somehow, a pointer to int >> gets replaced by a pointer to vector, even though their alignment >> properties are different. > > No, they are not. They get replaced if they are value-equivalent > in which case they are also alignment-equivalent. But well, the > dump snippet wasn't complete and I don't feel like building a > SPU cross to verify myself.
I am attaching the complete file. Thanks, Ira > >> This vector pointer must originate somehow in the vectorizer, >> however, since the original C source does not contain any >> vector types at all ... > > That's for sure true, it must be the initial pointer we then increment > in the vectorized loop. > > Richard. > >> Bye, >> Ulrich >> >> -- >> Dr. Ulrich Weigand >> GNU Toolchain for Linux on System z and Cell BE >> ulrich.weig...@de.ibm.com >> >
my--pr49771.c.124t.dom2
Description: Binary data
#include <stdio.h>
#include <stdarg.h>
#define N 4
static int a[N];
__attribute__ ((noinline)) int
foo (void)
{
int j;
int i;
for (i = 0; i < N; i++)
for (j = 0; j < N; j++)
a[j] = a[i] + 1;
return a[0];
}
int
main (void)
{
int res, i;
for (i = 0; i < N; i++)
a[i] = 0;
res = foo ();
if (res != 31)
printf ("%d\n", res);
for (i = 0; i < N; i++)
printf ("%d ", a[i]);
printf ("\n");
return 0;
}
/* { dg-final { cleanup-tree-dump "vect" } } */
