Dead Store Elimination

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

Controlling dead store elimination 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 an Optimization Level value `(3,4)` from the Properties > C/C++ Build > Settings > Tool Settings > PowerPC Compiler > Optimization panel.
source code	`#pragma opt_dead_assignments on \| off \| reset`
command line	`-opt [no]deadstore`

For example, in Before dead store elimination 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() .

In After dead store elimination the compiler can safely remove the first assignment to x since the result of this assignment is never used.

Figure 1. Before dead store elimination

void func_from(int x, int y)
{
    x = y * y;
    otherfunc1(y);
    x = getresult();
    otherfunc2(y);
}

Figure 2. After dead store elimination

void func_to(int x, int y)
{
    otherfunc1(y);
    x = getresult();
    otherfunc2(y);
}