The impact of patches 4-9 of the patch set on the example from the bug report for ARM Thumb-2 -Os is a further size reduction of 7%, from 58 to 54 bytes.
This size reduction is illustrated in this diff of the assembly (left, without patches, size 58. right, with patches, size 54): ... push {r3, r4, r5, r6, r7, push {r3, r4, r5, r6, r7, mov r7, r1 mov r7, r1 mov r6, r2 mov r6, r2 movs r1, #0 movs r1, #0 movs r2, #1 movs r2, #1 mov r5, r0 mov r5, r0 bl lseek bl lseek movs r1, #0 movs r1, #0 movs r2, #2 movs r2, #2 mov r4, r0 mov r4, r0 mov r0, r5 mov r0, r5 bl lseek bl lseek adds r2, r4, #1 adds r2, r4, #1 beq .L3 | beq .L5 adds r3, r0, #1 adds r3, r0, #1 beq .L2 beq .L2 subs r0, r0, r4 subs r0, r0, r4 beq .L5 beq .L5 str r4, [r7, #0] str r4, [r7, #0] str r0, [r6, #0] str r0, [r6, #0] movs r0, #0 movs r0, #0 pop {r3, r4, r5, r6, r7, pop {r3, r4, r5, r6, r7, .L3: < mov r0, r4 < pop {r3, r4, r5, r6, r7, < .L5: .L5: mov r0, #-1 mov r0, #-1 .L2: .L2: pop {r3, r4, r5, r6, r7, pop {r3, r4, r5, r6, r7, ... The patches 4-9 allows crossjumping: - to recognize that 'mov r0, r4' and 'move r0, #-1' have the same effect, and - to extend the search scope past label .L2 backward to .L5, in order to recognize that the jump to .L3 can be replaced with a jump to .L5. Thanks, - Tom