git log -S

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.

Binary files are searched as well.