Your posted code has some problems:

• It does not compile. There's a problem with the statement
     my $b = qr{  abc_p | abc) }xms;
  (already noted by LanX).
• Your test data does not include an instance of the 'int abc;' input variation.
• More of an annoyance than a problem: AFAICT, you have never said what version of Perl you are running under.
• Even more annoying: You still are not posting in a Test::More format.

A general point: Don't you see that you are trying to process two basically different patterns? 'int abc;' gets altered (apparently) unconditionally, but '.abc(abc_p)' gets altered only if the 'abc' or 'abc_p' pattern is repeated. Recognizing the patterns you're dealing with is the first step toward solving this (or any) regex problem.