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AN3350

Intermediate optimizations

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Intermediate optimizations

After it translates a program’s source code into its intermediate representation, the compiler

optionally applies optimizations that reduce the program’s size, improve its execution speed,

or both. The topics in this chapter explains these optimizations and how to apply them:

●

Intermediate optimizations

●

Inlining

13.1

Intermediate optimizations

After it translates a function into its intermediate representation, the compiler may optionally

apply some optimizations. The result of these optimizations on the intermediate

representation will either reduce the size of the executable code, improve the executable

code’s execution speed, or both.

●

Dead code elimination

●

Expression simplification

●

Common subexpression elimination

●

Copy propagation

●

Dead store elimination

●

Live range splitting

●

Loop-invariant code motion

●

Strength reduction

●

Loop unrolling

13.1.1

Dead code elimination

The dead code elimination optimization removes expressions that are not accessible or are

not referred to. This optimization reduces size and increases execution speed.

Table 17 explains how to control the optimization for dead code elimination.

In Example 49, the call to func1() will never execute because the if statement that it is

associated with will never be true. Consequently, the compiler can safely eliminate the call

to func1(), as shown in Example 50.

Example 49 Before dead code elimination

void func_from(void)

{

if (0)

{

Table 17.

Controlling dead code elimination

Turn control this option from here...

use this setting

Source code

#pragma opt_dead_code on | off | reset

Command line

-opt [no]deadcode

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