CHAPTER 13. SWITCH()/CASE/DEFAULT CHAPTER 13. SWITCH()/CASE/DEFAULT
It is also worth noting that the code is generated as a separate function in order to reuse it, so the compiler not generates
the same code for every switch() statement.
IDAsuccessfully perceived it as a service function and a table, and added comments to the labels like
jumptable 000000FA case 0.
13.2.4 MIPS.
Listing 13.8: Optimizing GCC 4.4.5 (IDA)f:
lui $gp, (gnu_local_gp >> 16)
; jump to loc_24 if input value is lesser than 5:
sltiu $v0, $a0, 5
bnez $v0, loc_24
la $gp, (gnu_local_gp & 0xFFFF) ; branch delay slot
; input value is greater or equal to 5.
; print "something unknown" and finish:
lui $a0, ($LC5 >> 16) # "something unknown"
lw $t9, (puts & 0xFFFF)($gp)
or $at, $zero ; NOP
jr $t9
la $a0, ($LC5 & 0xFFFF) # "something unknown" ; branch delay slot
loc_24: # CODE XREF: f+8
; load address of jumptable
; LA is pseudoinstruction, LUI and ADDIU pair are there in fact:
la $v0, off_120
; multiply input value by 4:
sll $a0, 2
; sum up multiplied value and jumptable address:
addu $a0, $v0, $a0
; load element from jumptable:
lw $v0, 0($a0)
or $at, $zero ; NOP
; jump to the address we got in jumptable:
jr $v0
or $at, $zero ; branch delay slot, NOP
sub_44: # DATA XREF: .rodata:0000012C
; print "three" and finish
lui $a0, ($LC3 >> 16) # "three"
lw $t9, (puts & 0xFFFF)($gp)
or $at, $zero ; NOP
jr $t9
la $a0, ($LC3 & 0xFFFF) # "three" ; branch delay slot
sub_58: # DATA XREF: .rodata:00000130
; print "four" and finish
lui $a0, ($LC4 >> 16) # "four"
lw $t9, (puts & 0xFFFF)($gp)
or $at, $zero ; NOP
jr $t9
la $a0, ($LC4 & 0xFFFF) # "four" ; branch delay slot
sub_6C: # DATA XREF: .rodata:off_120
; print "zero" and finish
lui $a0, ($LC0 >> 16) # "zero"
lw $t9, (puts & 0xFFFF)($gp)
or $at, $zero ; NOP
jr $t9
la $a0, ($LC0 & 0xFFFF) # "zero" ; branch delay slot
sub_80: # DATA XREF: .rodata:00000124
; print "one" and finish
lui $a0, ($LC1 >> 16) # "one"
lw $t9, (puts & 0xFFFF)($gp)
or $at, $zero ; NOP
jr $t9