I'm not sure I get the question (or the relation to vi), but if you're just talking about reformatting code as shown in your example, here's one way:

{
    local $/;  # go to slurp mode for input
    open( I, "<", "my_source_code" ) or die "my_source_code: $!";
    $_ = <I>;
    close I;

    s/(if.*?)\s+{/$1 {/g;    # fix spacing/line-breaks for "if .... {"

    open( O, ">", "my_new_source_code" ) or die "my_new_source_code: $
+!";
    print O;
    close O;
}
[download]

Obviously, if the data being edited contains stuff like this:

if ( "blah { blah } blah" )

{
...
[download]

then it will get seriously screwed up simply not do what you intended, so maybe something more constrained:

     s/(if.*?\))[ \r\t]*\n\s+{/$1 {/;  # fix spacing/line-breaks for "
+if (...) {"
[download]

which involves looking specifically for "if" plus some minimal number of non-line-break characters, followed by close-paren, followed a line-break (which might be surrounded by other kinds of whitespace). Even then, it's worth checking to see that the input and output meet your expectations.

(updated second s/// example to include "\r")