For the H8/300, ld can perform these global optimizations when you specify the ‘--relax’ command-line option.
jsr and jmp instructions whose
targets are within eight bits, and turns them into eight-bit
program-counter relative bsr and bra instructions,
respectively.
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).
ld finds all mov instructions which use the register
indirect with 32-bit displacement addressing mode, but use a small
displacement inside 16-bit displacement range, and changes them to use
the 16-bit displacement form. (That is: the linker turns ‘mov.b
@d:32,ERx’ into ‘mov.b @d:16,ERx’
whenever the displacement d is in the 16 bit signed integer
range. Only implemented in ELF-format ld).
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).
ldc.w, stc.w instructions 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).