Every mojo execution, if it specifies dependency resolution other than 'none', will cause a resolution to be performed.
There is a guard in MojoExecutor's DependencyContext which guards against performing this resolution multiple times by looking at the changes to dependencyArtifacts list.
However, during a build in an incremental/interactive environment, like eclipse m2e or maven console, those mojos might be executed at an arbitrary time and will not benefit from that DependencyContext check.
I propose having a ProjectArtifactsCache (very similar to PluginArtifactsCache) that will cache artifact set as returned by LifecycleDependencyResolver#getDependencies().
While it does not improve cli builds, incremental/interactive builds will receive a huge performance boost between pom changes.
I've been able to get build of a project with a lot of dependencies (jenkins plugin) and a number of (fully incremental) mojo executions from 7 seconds to around 1.5 on a single java file change in eclipse m2e after introducing this cache.
I will provide a patch shortly.