Our incremental build performance has degraded a lot recently. On Windows it's especially bad (as usual). There are multiple issues. Some cases of running way too many find/grep during rule setup. Some files get rebuilt on every incremental build.

We also have a rather inefficient pattern where a makefile is responsible for two top level targets, the general build of something and then the copying of that something into images. The drawback of this pattern is that all the rules in the makefile get evaluated twice, and this is potentially expensive. My workaround for this is to enclose the expensive parts in conditionals that check what target the makefile was called with.