[PATCH] D142279: [cmake] Use LLVM_ENABLE_ASSERTIONS to enable assertions in libstdc++

Mon Jan 30 02:25:21 PST 2023

rovka added a comment.

In D142279#4088057 <https://reviews.llvm.org/D142279#4088057>, @foad wrote:

> I've investigated a bit more. It's a difference between libstdc++-11 and libstdc++-12, caused by this patch:
>
> https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=a54ce8865a885bca5ab9c4aa6ec725cd13c09901
>
> Previously a failed assertion would print a message with `__builtin_printf`. Now it prints a message by calling `__glibcxx_assert_fail` which is defined in the library.
>
> What's the way forward for the flang runtime library? Can we disable libstdc++ assertions? Can we provide our own implementation of __glibcxx_assert_fail?

Well, the flang runtime library definitely doesn't want <https://flang.llvm.org/docs/IORuntimeInternals.html#:~:text=it%20is%20intended%20to%20not%20have%20any%20link%2Dtime%20dependences%20on%20the%20C%2B%2B%20runtime%20support%20library> a dependency on libstdc++.

I'm not sure what to say about enabling or disabling the libstdc++ assertions. What do other runtimes do? It might be sensible to disable them, since flang users wouldn't be able to control this and may not even be aware of whether or not their build of flang was built with assertions enabled. From what I can see, for now the assertions only appear in the IO part of the runtime, so we wouldn't be introducing unwanted asserts in people's performance-sensitive code, but it still feels safer to disable these for the runtime libraries (FortranRuntime and FortranDecimal).

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