Size optimizations for Assembly

Question

What other optimizations, like the one presented here http://stackoverflow.com/questions/147173/x86-assembly-testl-eax-against-eax can one apply in order to reduce code size?

I am interested especially in one-line optimizations like using test eax, eax instead of cmp eax, 0.

Thanks.

Answer 1

Moving some constants into registers can be done more efficiently without using mov. For instance, to move zero into rax:

xor eax, eax

Or to set rax to one:

xor eax, eax
inc eax

eax (rather than rax) can be used since the upper half of rax is implicitly cleared (thanks for the comment)

Answer 2

I found another one:

add eax, 1

replaced with

inc eax

Answer 3

Moving constant signed bytes (-128 to 127) to registers can be used with push and pop to save a couple of bytes.

6A09         push byte 9     ; Push byte 9 on stack
58           pop eax         ; Pop into 32-bit eax

That's three bytes in comparsion to the mov five byte equivalent

B809000000   mov eax, 9