A makefile consists of rules. Each rule contains a dependency line which defines a target and an enumeration of prerequisites. This means that the dependencies have to be known before the target is built. By design, it is impossible for a single-pass make(1) invocation to derive dependencies for a C program, as dependencies are output by the compiler.

By contrast, redo builds the target first and then records what was used to build it. For example, when compiling a C file with “gcc -M”, gcc will output dependency information. With redo, you normally record those dependencies after the target has been built. With make(1), that information has to end up in the makefile somehow, possibly leading to further builds.