List the compiler optimization techniques and code optimization techniques

Use the appropriate optimization technique for optimizing the following codes

int add $($int x$,$ int y$)$

$\{$

return x $+$ y;

$\}$

int sub $($int x$,$ int y$)$

$\{$

return add $($x$,-$y$)$;

$\}$

int global;

void f $()$

l

int i;

i $=1$; $/*$ dead store $*/$

global $=1$; $/*$ dead store $*/$

global $=2$;

return;

global $=3$; $/*$ unreachable $*/$

$\}$

i $=0$;

j $=0$;

for $($i$=0$;i$<mn>4</mn><mn>5</mn>$;i$++)$

l

arr$[$j$]=$ j;

j$++$

for $($i$=0$; i$<mtext></mtext><mn>4</mn><mn>5</mn>$; i$++)$

$\{$

arr$2[$j$]=$ j;

j$++$;

$\}$ solve and optimize with proper steps and reason no ai or chat gpt otherwise dislike