Help for target with BITS_PER_UNIT = 16

[Mohamed Shafi <shafitvm@gmail.com>]

Hello all,

I am trying to port GCC 4.5.1 for a processor that has the following
addressing capability:

The data memory address space of 64K bytes is represented by a total
of 15 bits, with each address selecting a 16-bit element. When using
the address register, the LSB of address reg (AD) points to a 16-bit
field in data memory. If a data memory line is 128 bits there are 8,
16-bit elements per data memory line. We use little endian addressing,
so
if AD=0, bits [15:0] of data memory line address 0 would be selected.
If AD=1, bits [31:16] of data memory line address 0 would be selected.
If AD=9, bits [31:16] of data memory line address 1 would be selected.

So if i have the following program

short arr[5] = {11,12,13,14,15};

int foo ()
{
    short a = arr[0] + arr[3];
    return a;
}

Assume that short is 16bits and short address is 2byte aligned.Then I
expect the following code to get generated:

mov a0,#arr       // Load the address

mov a1, a0        // Copy the address
add a1, 1          // Increment the location by 1 so that the address
points to arr[1]
ld.16 g0, (a1)    // Load the value 12 into g0

mov a1, a0        // Copy the address
add a1, 3          // Increment the location by 3 so that the address
points to arr[3]
ld.16 g1, (a1)    // Load the value 14 into g0

add g1, g1, g0  // Add 12 and 14

For the following code:

short arr[5] = {11,12,13,14,15};

int foo ()
{
short a,b;

a = (short) (&arr[3] - &arr[1]); // a is 2 after this operation
b = (short) ((char*)&arr[3] - (char*)&arr[1]);  // b is 4 after this operation

return a;
}

My question is should i set the macro BITS_PER_UNIT = 16 to get a code
generated like this? From IRC chat i realize that  BITS_PER_UNIT != 8
is seriously rotten. If that is the case how can i proceed to port
this target?

Regards,
Shafi