In a past life I worked on a COBOL compiler for IBM. There is a COBOL specification, but AFAIK nobody actually implements it fully. Implementations pick and ch

In a past life I worked on a COBOL compiler for IBM. There is a COBOL specification, but AFAIK nobody actually implements it fully. Implementations pick and choose new features based on customer demand. Also, COBOL is dominated by large legacy codebases, which means that if there's a discrepancy between an implementation and the specification, the users normally don't want it fixed, because they may have written code that depends on the "incorrect" behaviour and it's a lot of work to audit. IBM built a new backend for its COBOL compiler using the optimizer from their JVM. IIRC by the time I left it generated code that was ~2x faster than the old compiler, but uptake was still slow because of migration concerns. In particular, we spent a lot of time working on features to help guarantee that code with some forms of undefined behaviour would have the same result as the old version.