Delayed Branch, Call, And Return Instructions - Texas Instruments TMS320C2x User Manual

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