mips-gcc : how to disable 8bit and 16bit memory accesses

[HEITZMANN Frédéric 218168]

Hi all,

I have been working on a MIPS-based platform, which incidently fails to read and write 8bit or 16bit integers, due to a very annoying HW bug.
In other words, any assembly instruction like lb, lbu, sb, lh ... turns to be a no-op.

A proper manual workaround is to rely on 32bits accesses with proper bit masks, but :
* I do not want to patch any existing code using char or short.
* I want to prevent gcc from optimizing code chunks like this one :
    int i = (*(int*)0x1234) & 0xFF;
into
    lb r0, 0x1237
(which it actually does, with -O2 or -Os).

I would like to tell gcc not to use lb, lbu ... but lw and sw with proper bit masks.
Incidently, I would like to optimize memory accesses when it is possible, e.g.
    char* a = (char*)0x1234;
    char c1 = *a;
    char c2 = *(a+1);
should generate only one read at 0x1234

=> Is it achievable by changing mips.md ?
=> If so, could someone give me a hint on how to do it ?
=> If not, where should I have a look ?

Thanks for your help,

--
Frederic Heitzmann