Xtensa bccz out of range

[ma261065]

I notice that if I put the @micropython.native decorator on my code, I sometimes get a xtensa bccz out of range error.

It seems to only happen if the decorated function gets too long.

I haven't noticed the code failing in any way, so am unsure if this is something that I need to worry about (although it sounds bad)

[peterhinch]

I haven't studied the xtensa arch, but I gather that executable code is run from iram the quantity of which is limited. Consequently the size of a native code module is restricted.

[ma261065]

Thanks Peter. I wonder if it is the size of the iram that is the issue, or the fact that it's trying to emit a relative jump that is out of range.

Here is the code that generates the error in asmxtensa.c:

if (as->base.pass == MP_ASM_PASS_EMIT && !SIGNED_FIT12(rel)) {
    printf("ERROR: xtensa bccz out of range\n");

The SIGNED_FIT12 macro is defined as:

#define SIGNED_FIT12(x) ((((x) & 0xfffff800) == 0) || (((x) & 0xfffff800) == 0xfffff800))

So it looks like it is checking if a jump is within -2048 to +2047 bytes, and if it's larger than that the error is emitted. This would explain why the error happens as the function increases in size - eventually the jump target is more than 2048 bytes away.

In any case, I guess my question really is whether this is affecting my code or not. If it gets this error does it mean that it just doesn't emit native code for that function and I don't get the speed-up that I was aiming for, or does it change the relative jump to an absolute jump to work around it (and this is just a warning), or does it generate "faulty" code that could cause data corruption?