[cfe-dev] Restrict for values that are not parameters

[Richard Smith]

On Fri, Mar 6, 2015 at 12:14 PM, Mark Schimmel <Mark.Schimmel at synopsys.com>
wrote:

>  I cannot get Clang to add noalias via a cast operation. This code does
> not produce any warnings, and I believe it’s legal, but the restrict
> qualifier is lost.  Am I incorrect about this code being legal?  Any idea
> why the qualifier is stripped?  (It is a contrived example. You could
> imagine address checking and two separate loops.)
>

We have no way to model this use of 'restrict' in our IR. Putting the
'restrict' on a function parameter should work. If you have an address
checks and two separate loops, you could try factoring the 'noalias' loop
out to a separate function.

 #define NOALIAS __restrict
>
> //#define NOALIAS __attribute__((noalias))
>
>
>
> void move(
>
>     int* velocity_x, int* velocity_y, int* velocity_z,
>
>     int* position_x,int* position_y,int* position_z,
>
>     int* acceleration_x, int* acceleration_y, int* acceleration_z,
>
>     int             time_step,
>
>     int            count,
>
>     int            stride )
>
> {
>
>     {
>
>         int* NOALIAS r_acceleration_x = (int* NOALIAS)acceleration_x;
>

The cast on the right-hand side does nothing; per C11 6.7.3/4, "The
properties associated with qualified types are meaningful only for
expressions that are lvalues."

         int* NOALIAS r_velocity_x     = (int* NOALIAS)velocity_x;
>
>         int* NOALIAS r_position_x     = (int* NOALIAS)position_x;
>
>         int* NOALIAS r_acceleration_y = (int* NOALIAS)acceleration_y;
>
>         int* NOALIAS r_velocity_y     = (int* NOALIAS)velocity_y;
>
>         int* NOALIAS r_position_y     = (int* NOALIAS)position_y;
>
>         int* NOALIAS r_acceleration_z = (int* NOALIAS)acceleration_z;
>
>         int* NOALIAS r_velocity_z     = (int* NOALIAS)velocity_z;
>
>         int* NOALIAS r_position_z     = (int* NOALIAS)position_z;
>
>
>
>         for (int i=0;i<count*stride;i+=stride)
>
>         {
>
>             r_velocity_x[i] += r_acceleration_x[i] * time_step;
>
>             r_velocity_y[i] += r_acceleration_y[i] * time_step;
>
>             r_velocity_z[i] += r_acceleration_z[i] * time_step;
>
>             r_position_x[i] += r_velocity_x[i]     * time_step;
>
>             r_position_y[i] += r_velocity_y[i]     * time_step;
>
>             r_position_z[i] += r_velocity_z[i]     * time_step;
>
>         }
>
>     }
>
> }
>
>
>
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>
>
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