Major New Features¶

• Clang supports use of a profile remapping file, which permits profile data captured for one version of a program to be applied when building another version where symbols have changed (for example, due to renaming a class or namespace). See the Clang Compiler User’s Manual for details.

Non-comprehensive list of changes in this release¶

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New Compiler Flags¶

• -fprofile-filter-files=[regexes] and -fprofile-exclude-files=[regexes].

  Clang has now options to filter or exclude some files when instrumenting for gcov-based profiling. See the Clang Compiler User’s Manual for details.

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Deprecated Compiler Flags¶

The following options are deprecated and ignored. They will be removed in future versions of Clang.

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Modified Compiler Flags¶

• As of clang 8, alignof and _Alignof return the ABI alignment of a type, as opposed to the preferred alignment. __alignof still returns the preferred alignment. -fclang-abi-compat=7 (and previous) will make alignof and _Alignof return preferred alignment again.

New Pragmas in Clang¶

• Clang now supports adding multiple #pragma clang attribute attributes into a scope of pushed attributes.

Attribute Changes in Clang¶

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Windows Support¶

• clang-cl now supports the use of the precompiled header options /Yc and /Yu without the filename argument. When these options are used without the filename, a #pragma hdrstop inside the source marks the end of the precompiled code.
• clang-cl has a new command-line option, /Zc:dllexportInlines-, similar to -fvisibility-inlines-hidden on non-Windows, that makes class-level dllexport and dllimport attributes not apply to inline member functions. This can significantly reduce compile and link times. See the User’s Manual for more info.
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C Language Changes in Clang¶

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C++ Language Changes in Clang¶

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Objective-C Language Changes in Clang¶

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OpenCL C Language Changes in Clang¶

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ABI Changes in Clang¶

• _Alignof and alignof now return the ABI alignment of a type, as opposed to the preferred alignment.
  • This is more in keeping with the language of the standards, as well as being compatible with gcc
  • __alignof and __alignof__ still return the preferred alignment of a type
  • This shouldn’t break any ABI except for things that explicitly ask for alignas(alignof(T)).
  • If you have interfaces that break with this change, you may wish to switch to alignas(__alignof(T)), instead of using the -fclang-abi-compat switch.

OpenMP Support in Clang¶

CUDA Support in Clang¶

Internal API Changes¶

These are major API changes that have happened since the 7.0.0 release of Clang. If upgrading an external codebase that uses Clang as a library, this section should help get you past the largest hurdles of upgrading.

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AST Matchers¶

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clang-format¶

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libclang¶

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Static Analyzer¶

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Undefined Behavior Sanitizer (UBSan)¶

• The Implicit Conversion Sanitizer (-fsanitize=implicit-conversion) group was extended. One more type of issues is caught - implicit integer sign change. (-fsanitize=implicit-integer-sign-change). This makes the Implicit Conversion Sanitizer feature-complete, with only missing piece being bitfield handling. While there is a -Wsign-conversion diagnostic group that catches this kind of issues, it is both noisy, and does not catch all the cases.

  bool consume(unsigned int val);
  
  void test(int val) {
    (void)consume(val); // If the value was negative, it is now large positive.
    (void)consume((unsigned int)val); // OK, the conversion is explicit.
  }
  

  Like some other -fsanitize=integer checks, these issues are not undefined behaviour. But they are not always intentional, and are somewhat hard to track down. This group is not enabled by -fsanitize=undefined, but the -fsanitize=implicit-integer-sign-change check is enabled by -fsanitize=integer. (as is -fsanitize=implicit-integer-truncation check)

Python Binding Changes¶

The following methods have been added:

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