Texas Instruments TMS320C2x, User Manual

Page: 86 / 250

What Kind of Optimization Is Being Performed?
3-17 Optimizing Your Code
Example 3 − 2. Delayed Branch, Call, and Return Instructions
main()
{
int i0, i1;
while (input(&i0) && input(&i1))
process(i0, i1);
}
TMS320C2x/C2xx/C5x C Compiler Output:
_main:
SAR AR0,*+ ; function prolog
POPD *+ ; save AR0 and return address
SAR AR1,* ; begin to set up local frame
BD L2 ; begin branch to loop control
LARK AR0,3 ; finish setting up local frame
LAR AR0,*0+
*** B L2 OCCURS ; branch to loop control
L1: ; loop body
LARK AR2,2 ; AR2 = &i1
MAR *0+
LAC *−,AR1 ; ACC = *AR2, AR2 = &i0
SACL *+,AR2 ; stack ACC
CALLD _process ; begin call
LAC * ,AR1 ; ACC = *AR2
SACL *+ ; stack ACC
*** CALL _process OCCURS ; call occurs
SBRK 2 ; pop stack
L2: ; loop control
MAR * ,AR5 ; AR5 = &i0
LARK AR5,1
CALLD _input ; begin call
MAR *0+,AR1
SAR AR5,*+ ; stack AR5
*** CALL _input OCCURS ; call occurs
MAR *− ; clear stack
BZ EPI0_1 ; quit if _input returns 0
MAR * ,AR4 ; AR4 = &i1
LARK AR4,2
CALLD _input ; begin call
MAR *0+,AR1
SAR AR4,*+ ; stack AR4
*** CALL _input OCCURS ; call occurs
MAR *−,AR2 ; clear stack
BNZ L1 ; continue if _input returns !0
EPI0_1:
MAR * ,AR1 ; function epilog
SBRK 4 ; clear local frame
PSHD *− ; push return address on hardware stack
RETD ; begin return
LAR AR0,* ; restore AR0
NOP ; necessary, no PSHD in delay slot
*** RET OCCURS ; return occurs
. . .