You are asserting that any time you interpolate a compiled re into another, it just stringifies the first anyway, and re-compiles the whole thing?
That's no assertion. That's how it works.
I had always assumed that it copies the compiled bits and does not need to re-process it.
No, that's not really possible to do (think for instance paren counts - or consider this: $q = qr/x/; $r = qr/[$q]/). It only works in this case: 
my $qr1 = /pattern/;
my $qr2 = /$qr1/;

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Use use re 'debug' and you will see what strings are being compiled.

In reply to Re^7: Composing regex's dynamically by JavaFan
in thread Composing regex's dynamically by John M. Dlugosz

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