[Bug tree-optimization/43001] New: Missed vectorization on ARM NEON

[steven at gcc dot gnu dot org]

Hello,

In late 2008 there was a post about a wrong-code bug on hardwarebug.org
(http://hardwarebug.org/2008/11/28/codesourcery-fails-again/#more-83). There
was this test case, and it was not vectorized correctly.

-----------------------

extern unsigned char dst[512] __attribute__((aligned(8)));
extern unsigned char src[512] __attribute__((aligned(8)));

void array_shift(void)
{
    int i;
    for (i = 0; i < 512; i++)
        dst[i] = src[i] >> 7;
}
-------------------


With GCC trunk of today, vectorization doesn't happen at all:
t.c:8: note: type of def: 3.
t.c:8: note: vect_is_simple_use: operand 7
t.c:8: note: vector/scalar shift/rotate found.
t.c:8: note: not worthwhile without SIMD support.
t.c:8: note: not vectorized: relevant stmt not supported: D.1963_4 = D.1962_3
>> 7;

t.c:8: note: bad operation or unsupported loop bound.
t.c:5: note: vectorized 0 loops in function.

Compiler is trunk r156595 for arm-elf.
Compiler options: "-mcpu=cortex-a8 -mfpu=neon -O3 -fdump-tree-vect-details"


-- 
           Summary: Missed vectorization on ARM NEON
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steven at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43001