4.1 ld and the H8/300

For the H8/300, ld can perform these global optimizations when you specify the --relax command-line option.

relaxing address modes

ld finds all jsr and jmp instructions whose targets are within eight bits, and turns them into eight-bit program-counter relative bsr and bra instructions, respectively.

synthesizing instructions

ld finds all mov.b instructions which use the sixteen-bit absolute address form, but refer to the top page of memory, and changes them to use the eight-bit address form. (That is: the linker turns mov.b @ aa :16 into mov.b @ aa :8 whenever the address aa is in the top page of memory).

bit manipulation instructions

ld finds all bit manipulation instructions like band, bclr, biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor which use 32 bit and 16 bit absolute address form, but refer to the top page of memory, and changes them to use the 8 bit address form. (That is: the linker turns bset #xx:3, @ aa :32 into bset #xx:3, @ aa :8 whenever the address aa is in the top page of memory).

system control instructions

ld finds all ldc.w, stc.w instrcutions which use the 32 bit absolute address form, but refer to the top page of memory, and changes them to use 16 bit address form. (That is: the linker turns ldc.w @ aa :32,ccr into ldc.w @ aa :16,ccr whenever the address aa is in the top page of memory).