[ADT] Replace std::isprint by llvm::isPrint.

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 platform-independent version.

Differential Revision: https://reviews.llvm.org/D49680

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338034 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 10 insertions, 1 deletions

diff --git a/include/llvm/ADT/StringExtras.h b/include/llvm/ADT/StringExtras.h
index b1596c54da5..71b0e7527cb 100644
--- a/include/llvm/ADT/StringExtras.h
+++ b/include/llvm/ADT/StringExtras.h
@@ -99,6 +99,15 @@ inline bool isASCII(llvm::StringRef S) {
   return true;
 }
 
+/// Checks whether character \p C is printable.
+///
+/// Locale-independent version of the C standard library isprint whose results
+/// may differ on different platforms.
+inline bool isPrint(char C) {
+  unsigned char UC = static_cast<unsigned char>(C);
+  return (0x20 <= UC) && (UC <= 0x7E);
+}
+
 /// Returns the corresponding lowercase character if \p x is uppercase.
 inline char toLower(char x) {
   if (x >= 'A' && x <= 'Z')
diff --git a/include/llvm/Support/raw_ostream.h b/include/llvm/Support/raw_ostream.h
index e54c8cc5d3e..b9ea9b5817f 100644
--- a/include/llvm/Support/raw_ostream.h
+++ b/include/llvm/Support/raw_ostream.h
@@ -220,7 +220,7 @@ public:
   raw_ostream &write_uuid(const uuid_t UUID);
 
   /// Output \p Str, turning '\\', '\t', '\n', '"', and anything that doesn't
-  /// satisfy std::isprint into an escape sequence.
+  /// satisfy llvm::isPrint into an escape sequence.
   raw_ostream &write_escaped(StringRef Str, bool UseHexEscapes = false);
 
   raw_ostream &write(unsigned char C);