[Bug c/53124] New: Arm NEON narrowing right shift instructions impose incorrect operand bounds (intrinsic and asm)

ksebov at rim dot com gcc-bugzilla@gcc.gnu.org
Wed Apr 25 19:57:00 GMT 2012


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53124

             Bug #: 53124
           Summary: Arm NEON narrowing right shift instructions impose
                    incorrect operand bounds (intrinsic and asm)
    Classification: Unclassified
           Product: gcc
           Version: 4.4.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ksebov@rim.com


The following code produces "Constant out of range" compiler error, even though
it's supposed to allow any immediate up to (size(datatype) - 1), or 31 in this
case. See
http://infocenter.arm.com/help/topic/com.arm.doc.dui0489c/CIHGJIHA.html

Using inline assembly implementation doesn't work either resulting in "Error:
immediate out of range for narrowing operation". 

int16x4_t rshift8_and_saturate_uint12( int32x4_t arg )
{
    uint32x4_t saturated_at32 = vqshluq_n_s32( arg, 32-(8+12) );
#if 1
    return vshrn_n_s32( vreinterpretq_s32_u32( saturated_at32 ), 32-12 );
#else
    int16x4_t result;
    asm volatile( "VSHRN.I32 %P0, %q1, #20" : "=w"(result) :
"w"(saturated_at32));
    return result;
#endif
}

It appears similar to http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41196
although in this case the ssembler code will probably need to be fixed as well.

Also, by looking at /gcc/config/arm/neon.md it seems all V[Q]SHR[U]N are
affected.



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