Git log command doesn't run as expected.

[周应天]

Hi,
        I’m using following command to do some search work:
        git log --all -G 'some regexp' -p — path/to/my/file.
But the output could miss some commit. (For example, I grep a little piece of 
code from a commit diff message(properly handled for regexp), but when I use 
the command above to search that code, I could not get that commit.)
        I wonder that it is because I use it in a wrong way? Then what should I 
do to correct it.

                                                                                
                                                                                
                        Thanks!