Dead Store Elimination

Dead store elimination removes unused assignment statements. This optimization reduces size and improves speed.

The following table explains how to control the optimization for dead store elimination.

Table 1. Controlling dead store elimination
Turn control this option from here...	use this setting
CodeWarrior IDE	Choose Level 3 or Level 4 in the Optimization Level settings panel.
source code	`#pragma opt_dead_assignments on \| off \| reset`
command line	`-opt [no]deadstore`

For example, in the following listing the variable x is first assigned the value of y * y. However, this result is not used before x is assigned the result returned by a call to getresult().

Listing: Before dead store elimination

void func_from(int x, int y)
{

    x = y * y;

    otherfunc1(y);

    x = getresult();

    otherfunc2(y);

}

In the following listing the compiler can safely remove the first assignment to x since the result of this assignment is never used.

Listing: After dead store elimination

void func_to(int x, int y)
{

    otherfunc1(y);

    x = getresult();

    otherfunc2(y);

}