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[Demangle] avoid more std::string_view::substr

Authored by nickdesaulniers on May 23 2023, 2:39 PM.



In D148959, I removed usage of std::string_view::substr because it may
throw, and libcxxabi cannot use such code. I missed one instance in
llvm::starts_with. That is blocking copying the code back upstream in

Mark these helpers noexcept (as they are in C++20) as well, to remind
future travelers.

Make these changes upstream, and copy them back downstream using

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front is not noexcept. Should I rewrite this to be &*self == C?

MaskRay added inline comments.May 23 2023, 3:29 PM

Ah, *self == C looks good. It's a pity that front throws...


size is more common than length.

philnik added inline comments.May 23 2023, 3:36 PM

front() doesn't throw. All major implementation also mark it as noexcept as a conforming extension. It's just not required to be noexcept in case an implementation wants to throw in the UB case.

  • replace front() with *begin(), length() with size()
nickdesaulniers marked 3 inline comments as done.May 24 2023, 12:24 PM
MaskRay accepted this revision.May 24 2023, 1:37 PM
MaskRay added inline comments.

if (needle.empty()) is a special case that can be handled by the generic code. It can be removed.

nickdesaulniers marked an inline comment as done.
  • remove special case for empty needle; it's already handled
ldionne accepted this revision.May 25 2023, 1:32 PM
This revision is now accepted and ready to land.May 25 2023, 1:32 PM
This revision was landed with ongoing or failed builds.May 25 2023, 2:35 PM
This revision was automatically updated to reflect the committed changes.