possible miscompilation on macOS Catalina 10.15.6

Niels Möller nisse at lysator.liu.se
Thu Oct 29 19:02:34 UTC 2020

Paul Koning <paulkoning at comcast.net> writes:

> There is another possibility: GMP might be doing something undefined,
> where previous compilers did "what we want" while some recent new ones
> do something different. It isn't miscompilation if the source
> statement is undefined.

As a general statement, that's hard to dispute. But previous experience
is that most problems like this boil down to compiler bugs, after
someone spends the time to investigate properly. 

And the compiler shipped with the initial release of MacOS "Catalina",
in particular, has known issues, if I don't misremember previous reports
on this list.

So you have to forgive GMP developers of not being thrilled at spending
our spare time investigating, in particular if it's a proprietary
compiler with known bugs in recent history.

GMP correctness depends on the compiler getting arithmetic right
including in edge cases not exercised by most applications, and it also
has a pretty thorough test suite that tends to detect compiler bugs.


Niels Möller. PGP-encrypted email is preferred. Keyid 368C6677.
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