Don't generate part of templates if we "know" (ie, we have literal's value) that it will never be entered

[GuillaumeGomez]

For example:

{% set x = true %}

{% if x %}
bla
{% else %}
blo
{% endif %}

In this case, we know for absolutely sure that it'll never enter the else block, so we could completely remove the condition.

Same could be done with other literals (like string).