Optimize Generated Code by Consolidating Redundant If-Else Statements
This example shows how to optimize generated code by combining if-else statements that share the same condition. This optimization:
Improves control flow.
Reduces code size.
Reduces RAM consumption.
Increases execution speed.
Example
The model rtwdemo_controlflow_opt contains three Switch blocks. The Constant block provides the control input to the Switch blocks. The variable named Cond determines the value of the Constant block.
model = 'rtwdemo_controlflow_opt';
open_system(model);
Generate Code
Create a temporary folder for the build and inspection process.
currentDir = pwd; [~,cgDir] = rtwdemodir();
Build the model.
rtwbuild(model)
### Starting build procedure for: rtwdemo_controlflow_opt ### Successful completion of build procedure for: rtwdemo_controlflow_opt Build Summary Top model targets built: Model Action Rebuild Reason ======================================================================================================== rtwdemo_controlflow_opt Code generated and compiled Code generation information file does not exist. 1 of 1 models built (0 models already up to date) Build duration: 0h 0m 12.571s
These lines of rtwdemo_controlflow_opt.c code show that in the generated code, two if-else statements and one else-if statement represent the three Switch blocks.
cfile = fullfile(cgDir,'rtwdemo_controlflow_opt_ert_rtw',... 'rtwdemo_controlflow_opt.c'); rtwdemodbtype(cfile,'/* Model step', '/* Model initialize', 1, 0);
/* Model step function */
void rtwdemo_controlflow_opt_step(void)
{
/* Switch: '<Root>/Switch3' incorporates:
* Constant: '<Root>/Const'
* Switch: '<Root>/Switch2'
*/
if (Cond) {
/* Switch: '<Root>/Switch1' */
if (Cond) {
/* Outport: '<Root>/Out1' incorporates:
* Inport: '<Root>/In1'
*/
rtY.Out1 = rtU.In1;
} else {
/* Outport: '<Root>/Out1' incorporates:
* Inport: '<Root>/In2'
*/
rtY.Out1 = rtU.In2;
}
/* End of Switch: '<Root>/Switch1' */
} else if (Cond) {
/* Switch: '<Root>/Switch2' incorporates:
* Inport: '<Root>/In1'
* Outport: '<Root>/Out1'
*/
rtY.Out1 = rtU.In1;
} else {
/* Outport: '<Root>/Out1' incorporates:
* Inport: '<Root>/In2'
*/
rtY.Out1 = rtU.In2;
}
/* End of Switch: '<Root>/Switch3' */
}
Enable Optimization
Open the Configuration Parameters dialog box.
On the Code generation-> Code Style pane, clear Preserve condition expression in if statement. This parameter is on by default.
Alternatively, use the command-line API to turn off the parameter:
set_param(model, 'PreserveIfCondition', 'off');
Generate Code with Optimization
In the optimized code, the code generator consolidates the two if-else statements and one else-if statement into one if-else statement. The code generator consolidates these statements because they all share the same condition. There is no intervening code that affects the outcomes of these statements.
Build the model.
rtwbuild(model)
### Starting build procedure for: rtwdemo_controlflow_opt ### Successful completion of build procedure for: rtwdemo_controlflow_opt Build Summary Top model targets built: Model Action Rebuild Reason ======================================================================================= rtwdemo_controlflow_opt Code generated and compiled Generated code was out of date. 1 of 1 models built (0 models already up to date) Build duration: 0h 0m 10.368s
Here is the rtwdemo_controlflow_opt.c optimized code.
rtwdemodbtype(cfile,'/* Model step', '/* Model initialize', 1, 0);
/* Model step function */
void rtwdemo_controlflow_opt_step(void)
{
/* Switch: '<Root>/Switch1' incorporates:
* Constant: '<Root>/Const'
* Switch: '<Root>/Switch3'
*/
if (Cond) {
/* Outport: '<Root>/Out1' incorporates:
* Inport: '<Root>/In1'
*/
rtY.Out1 = rtU.In1;
} else {
/* Outport: '<Root>/Out1' incorporates:
* Inport: '<Root>/In2'
*/
rtY.Out1 = rtU.In2;
}
/* End of Switch: '<Root>/Switch1' */
}
Close the model and clean up.
bdclose(model) rtwdemoclean; cd(currentDir)
See Also
Preserve condition expression in if statement