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[ADT] Replace std::isprint by llvm::isPrint.
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Authored by Meinersbur on Jul 23 2018, 10:27 AM.

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Summary

The standard library functions isprint/std::isprint have platform- and locale-dependent behavior which makes LLVM's output less predictable. In particular, regression tests my fail depending on the implementation of these functions.

Implement llvm::isPrint in StringExtras.h with a standard behavior and replace all uses of isprint/std::isprint by a call it llvm::isPrint. The function is inlined and does not look up language settings so it should perform better than the standard library's version.

Such a replacement has already been done for isdigit, isalpha, isxdigit in r314883. gtest does the same in gtest-printers.cc using the following justification:

// Returns true if c is a printable ASCII character.  We test the
// value of c directly instead of calling isprint(), which is buggy on
// Windows Mobile.
inline bool IsPrintableAscii(wchar_t c) {
  return 0x20 <= c && c <= 0x7E;
}

Similar issues have also been encountered by Julia: https://github.com/JuliaLang/julia/issues/7416

I noticed the problem myself when on Windows isprint('\t') started to evaluate to true (see https://stackoverflow.com/questions/51435249) and thus caused several unit tests to fail. The result of isprint doesn't seem to be well-defined even for ASCII characters. Therefore I suggest to replace isprint by a system-independent version.

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Event Timeline

Meinersbur created this revision.Jul 23 2018, 10:27 AM
This revision is now accepted and ready to land.Jul 23 2018, 12:40 PM

Rebase to r338031 before commit

This revision was automatically updated to reflect the committed changes.