What is not there
Dead-code elimination is the one optimizer pass that actively destroys evidence. A local that is assigned and never read does not become a shorter instruction sequence — it becomes nothing at all, and the target you are matching contains no hint that the original C ever mentioned it.
gcc 2.9 knows which operations are side-effect free, and that list includes the libgcc helpers. So an unused divide leaves nothing at all: the bl __divsi3 goes, and the whole frame it would have needed goes with it.
Here are two functions that differ in one character — whether the final sum reads v or t:
0 add r0, r1
2 bx lr
That is s32 t = v / w; return v + w;. The division is gone. No helper call, no push, no interworking epilogue: two instructions, because nothing ever looks at t.
0 push {r4, lr}
2 mov r4, r1
4 bl __divsi3-4
8 add r0, r4
10 pop {r4}
12 pop {r1}
14 bx r1
Same divide, now read once, and the function costs seven instructions and a callee-saved register. The lesson for matching is blunt: never add an operation to your C because you feel it ought to be there. If the target does not show it, the target does not contain it.
A call is the exception, and it goes the other way. gcc cannot prove an external function is side-effect free, so a bl survives even when its result is discarded — and discarding the result changes nothing about the frame. What the frame pays for is the values that must still be alive when the callee returns: each one gets copied into a callee-saved register on the way in and read back on the way out.
Your target makes that call and ignores what comes back. Work out from the push list how many values had to survive it, and notice that one of them is handed to the callee as well.
Your task
Write func_083c588c to reproduce the target assembly.