Well, it turns out that I can't use define_split for AND, since GCC requires exactly two RTL expressions after the split. Unfortunately, I need three split expressions for AND. What ends up happening in that case is that the entire split pattern is ignored, and errors are emitted during compilation.

What I ended up doing was to use the ANDHI3 pattern for these AND expressions, and use unnamed patterns for ANDI and AND with an inverted operand. As a named pattern, I can demand scratch registers. The unnamed patterns are only invoked if they match exactly, so they can't use scratches. This seems to work pretty well. Here's the output for "int and_mem_mem() {return(memb_a & memb_b);}":

and_mem_mem
movb @memb_b, r1
movb @memb_a, r2
inv r2
szcb r2, r1
sra r1, 8
b *r11

The instruction order is slightly different than I expected, but this is perfectly fine. The word AND forms have been modifified to match the changes I made to the byte forms.

With this out of the way, I can make a new set of patches and update the documentation. It looks like people are getting interested in using the compiler for their own projects, and I need to make sure all the information they might need is correct and available.