With Git, I find the pickaxe tool ("git log -S") to be useful for this purpose. From the man page:

-S<string>

    Look for differences that change the number of occurrences of the specified string (i.e. addition/deletion) in a file. Intended for the scripter’s use.

    It is useful when you’re looking for an exact block of code (like a struct), and want to know the history of that block since it first came into being: use the feature iteratively to feed the interesting block in the preimage back into -S, and keep going until you get the very first version of the block.