#2913 struct access on pic14 produces dubious code

[Herbert Pötzl]

On pic14, the following 'simple' structure assignment ...

#define NO_BIT_DEFINES
#include <pic16f1459.h>

void main(void)
{
    OSCCONbits.SCS = 0b01;
}

... results in unpectedted instructions ...

        MOVLW   (_OSCCONbits + 0)
        ANDLW   0xfc
        IORLW   0x01
        BANKSEL _OSCCONbits
        MOVWF   (_OSCCONbits + 0)

... where it should produce a similar sequence to the pic16 version ...

        BANKSEL _OSCCONbits
        MOVF    _OSCCONbits, W
        ANDLW   0xfc
        IORLW   0x01
        MOVWF   _OSCCONbits

... naturally the resulting code does not work as expected.

Best,
Herbert

[Herbert Pötzl]

I narrowed the issue down to a change between 3.6.0 and 3.7.0 where a condition was modified with dramatic results ...

https://sourceforge.net/p/sdcc/code/9836/tree//trunk/sdcc/src/pic14/gen.c?diff=513f4d42271846342871488b:9835

Here the last hunk (and especially the || part with PO_IMMEDIATE seems to be the problem, because the following patch seems to 'fix' the issue: http://vserver.13thfloor.at/Stuff/SDCC/sdcc-pic14-immediate.diff

Note that IMHO all pic14 MCUs are affected and I'm really surprised that nobody noticed this problem which has been there for quite some while.

Hope this helps,
Herbert

[Philipp Klaus Krause]

Could you check if the bug is also present in the pic14 branch?

Philipp

[Herbert Pötzl]

https://sourceforge.net/p/sdcc/code/HEAD/tree/branches/pic14/sdcc/src/pic14/gen.c certainly shows the || PO_IMMEDIATE in line 7995.