[intellij-idea] How can I give the Intellij compiler more heap space?

In my case the error was caused by the insufficient memory allocated to the "test" lifecycle of maven. It was fixed by adding <argLine>-Xms3512m -Xmx3512m</argLine> to:

<pluginManagement>
  <plugins>
    <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>2.16</version>
        <configuration>
            <argLine>-Xms3512m -Xmx3512m</argLine>

Thanks @crazycoder for pointing this out (and also that it is not related to IntelliJ; in this case).

If your tests are forked, they run in a new JVM that doesn't inherit Maven JVM options. Custom memory options must be provided via the test runner in pom.xml, refer to Maven documentation for details, it has very little to do with the IDE.