William "Chops" Westfield wrote:

> On May 27, 2011, at 2:47 PM, Gerhard Fiedler wrote:
>=20
>>> PORTB |=3D 2 had better compile to a single BSF instruction when
>>> possible (for example), or you go yell at the compiler vendor.)
>>=20
>> [compiler documentation] should in enough detail address everything
>> that is not standard C -- for example, how it handles bits, ports,
>> stack, variable banks, recursion, pointers etc.=20
>>=20
>> Don't go yell at the vendor before having read the docs... :)
>=20
> Current philosophy seems to be that a compiler should produce good =20
> code from STANDARD C constructs, without having to resort to non-=20
> standard bit-set macros. avr-gcc had deprecated sbi/cbi "functions" in =20
> favor of "just use var |=3D/&=3D~ bit", for example.

This is probably true, and it is a good thing. However, it is still in
"implementation-defined" land (that is, outside of what is specified in
the C language standard), and if you want to know what your compiler
does here, you have to consult the documentation.=20

For example, PORTB |=3D 2; resulting in a BSF instruction on a PIC is
expected, but with PORTB |=3D 3; things are not so clear anymore.

> After all, part of the point of using a C compiler is portability.
> Non-standard architecture-specific features should be avoided
> whenever possible.

Yes, but so should be architecture-specific expectations -- unless they
are founded in documentation or otherwise acquired knowledge of the
specific compiler :)

Gerhard
--=20
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