SUMMARY

Displays why deadcode elimination was partially disabled by the Go linker.

The Go linker will disable most deadcode elimination if it finds reachable calls to reflect.Value.MethodByName (that don't pass a constant string), reflect.Value.Method or reflect.Value.Methods. This is done because, using these two methods it is possible to dynamically call any public method in the application. Whydeadcode uses the call graph produced by the linker to display why reflect.Value.MethodByName, reflect.Value.Method or refect.Value.Methods (or a function that performs an inlined call to one of those methods) are reachable. Use it like this:

go build -ldflags=-dumpdep your/package |& whydeadcode

Needs Go 1.21 or later.

Because of how -dumpdep works only the first result output by whydeadcode is real. Because of how -dumpdep works anything beyond the first result can be a false positive (i.e. things that look like they will affect deadcode elimination but won't if the first result is taken care of) and it can also have false negatives (i.e. things that will continue to keep deadcode elimination disabled if the first result is taken care of).

USAGE

$ whydeadcode -h
Usage of whydeadcode:
        go build -ldflags=-dumpdep ... |& whydeadcode
  -fail
        Fail on non-empty findings
  -ignore-unrecognized-input
        Ignore unrecognized input

TALK

For a more detailed explanation see the golab 2023 talk or the slides (but see the talk update).