[sdcc-devel] iCode generator question

[Vangelis R. <vr...@ot...>]

 Hello all,
 I have a question about the iCode generator...
I try to compile the following source

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

volatile struct {
 unsigned RA0:1;
 unsigned RA1:1;
 unsigned RA2:1;
 unsigned RA3:1;
 unsigned RA4:1;
 unsigned RA5:1;
 unsigned RA6:1;
 unsigned RA7:1;
} TEST;

sfr at 0xf80 PORTA;
sfr at 0xf81 PORTB;

char a; //, c=0x1;

void main(void)
{
  char b;
  char c=0xc1;

 TEST.RA4 = (char)0x01;

 a = TEST.RA0;
 PORTB = TEST.RA0;
 b = PORTB;

 c += a | b;

 PORTB = c+0x25;
}
-------------------------------------

Its use, like many other major projects, is of now use, but it helps to
identify a problem.

Lets see the iCodes generated after the register allocation pass (the
.dumprassign file):

-------------------------------------
s7.c(l18:s1:k0:d0:s0)  _entry($2) :
s7.c(l18:s2:k1:d0:s0)  proc _main [k1 lr0:0 so:0]{ ia0 re0 rm0 nos0 ru0
dp0}{void function    ( ) }
s7.c(l23:s3:k3:d0:s0)  iTemp2 [k7 lr3:4 so:0]{ ia0 re0 rm1 nos0 ru0
dp0}{volatile-unsigned-bitfield {4,1} near* }[remat] = &[_TEST [k4 lr0:0
so:0]{ ia0 re0 rm0 nos0 ru0 dp0}{volatile-struct __00010000}]
s7.c(l23:s4:k5:d0:s0)  *(iTemp2 [k7 lr3:4 so:0]{ ia1 re0 rm1 nos0 ru0
dp0}{volatile-unsigned-bitfield {4,1} near* }[remat]) := 0x1
{literal-volatile-unsigned-bitfield {4,1}}

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

(note that I have deleted some lines from the beginning and the end of the
file to isolate the lines in request, but I attach the whole file for those
interested)

Lets isolate lines 3 and 4 and remove some useless stuff:

line 2: iTemp2 {volatile-unsigned-bitfield {4,1} near* }[remat] = &[_TEST
{volatile-struct __00010000}]
line 3: *(iTemp2 {volatile-unsigned-bitfield {4,1} near* }[remat]) := 0x1
{literal-volatile-unsigned-bitfield {4,1}}

I remind you that the line above represent the assignment: TEST.RA4 =
(char)0x01;

Question No1:
What does 'remat' means? And what is its use in the iCode generator? (i.e.
why it is used? what is its purpose?)


Question No2:
As far as I have understood the 8051 architecture has a bit space, so one
can acquire a pointer to a specific bit and assign a value to it. That's
what the currect iCode generator does.
But, there are other processors, like the PICs (and AVR I think) that do not
have this feature. On the other hand they have commands like SET_BIT and
CLEAR_BIT, that could be used for such purposes. The above implementation is
not suitable for these processors.
So is there a way to handle such a problem, or all the wight should be
thrown to the port code generator?
I would be nice if there was an option in the port structure that informs
the iCode generator to create a different iCode series that the above.

Thanks in advance,
Vangelis Rokas