Major New Features¶

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Non-comprehensive list of changes in this release¶

• For the ARM target, C-language intrinsics are now provided for the full Arm v8.1-M MVE instruction set. <arm_mve.h> supports the complete API defined in the Arm C Language Extensions.

New Compiler Flags¶

• -fstack-clash-protection will provide a protection against the stack clash attack for x86 architecture through automatic probing of each page of allocated stack.
• -ffp-exception-behavior={ignore,maytrap,strict} allows the user to specify the floating-point exception behavior. The default setting is ignore.
• -ffp-model={precise,strict,fast} provides the user an umbrella option to simplify access to the many single purpose floating point options. The default setting is precise.

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¶

• -fno-common has been enabled as the default for all targets. Therefore, C code that uses tentative definitions as definitions of a variable in multiple translation units will trigger multiple-definition linker errors. Generally, this occurs when the use of the extern keyword is neglected in the declaration of a variable in a header file. In some cases, no specific translation unit provides a definition of the variable. The previous behavior can be restored by specifying -fcommon.
• -Wasm-ignored-qualifier (ex. asm const (“”)) has been removed and replaced with an error (this matches a recent change in GCC-9).
• -Wasm-file-asm-volatile (ex. asm volatile (“”) at global scope) has been removed and replaced with an error (this matches GCC’s behavior).
• Duplicate qualifiers on asm statements (ex. asm volatile volatile (“”)) no longer produces a warning via -Wduplicate-decl-specifier, but now an error (this matches GCC’s behavior).

New Pragmas in Clang¶

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Attribute Changes in Clang¶

• Attributes can now be specified by clang plugins. See the Clang Plugins documentation for details.

Windows Support¶

C Language Changes in Clang¶

• The default C language standard used when -std= is not specified has been upgraded from gnu11 to gnu17.
• Clang now supports the GNU C extension asm inline; it won’t do anything yet, but it will be parsed.
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C++ Language Changes in Clang¶

• Clang now implements a restriction on giving non-C-compatible anonymous structs a typedef name for linkage purposes, as described in C++ committee paper P1766R1 <http://wg21.link/p1766r1>. This paper was adopted by the C++ committee as a Defect Report resolution, so it is applied retroactively to all C++ standard versions. This affects code such as:

  typedef struct {
    int f() { return 0; }
  } S;
  

  Previous versions of Clang rejected some constructs of this form (specifically, where the linkage of the type happened to be computed before the parser reached the typedef name); those cases are still rejected in Clang 11. In addition, cases that previous versions of Clang did not reject now produce an extension warning. This warning can be disabled with the warning flag -Wno-non-c-typedef-for-linkage.

  Affected code should be updated to provide a tag name for the anonymous struct:

  struct S {
    int f() { return 0; }
  };
  

  If the code is shared with a C compilation (for example, if the parts that are not C-compatible are guarded with #ifdef __cplusplus), the typedef declaration should be retained, but a tag name should still be provided:

  typedef struct S {
    int f() { return 0; }
  } S;
  

Objective-C Language Changes in Clang¶

OpenCL C Language Changes in Clang¶

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ABI Changes in Clang¶

OpenMP Support in Clang¶

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CUDA Support in Clang¶

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Internal API Changes¶

These are major API changes that have happened since the 10.0.0 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.

Build System Changes¶

These are major changes to the build system that have happened since the 10.0.0 release of Clang. Users of the build system should adjust accordingly.

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AST Matchers¶

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clang-format¶

• Option IndentCaseBlocks has been added to support treating the block following a switch case label as a scope block which gets indented itself. It helps avoid having the closing bracket align with the switch statement’s closing bracket (when IndentCaseLabels is false).

• Option ObjCBreakBeforeNestedBlockParam has been added to optionally apply linebreaks for function arguments declarations before nested blocks.

  switch (fool) {                vs.     switch (fool) {
  case 1:                                case 1: {
    {                                      bar();
       bar();                            } break;
    }                                    default: {
    break;                                 plop();
  default:                               }
    {                                    }
      plop();
    }
  }
  

• Option InsertTrailingCommas can be set to TCS_Wrapped to insert trailing commas in container literals (arrays and objects) that wrap across multiple lines. It is currently only available for JavaScript and disabled by default (TCS_None).

• Option BraceWrapping.BeforeLambdaBody has been added to manage lambda line break inside function parameter call in Allman style.

  true:
  connect(
    []()
    {
      foo();
      bar();
    });
  
  false:
  connect([]() {
      foo();
      bar();
    });
  

libclang¶

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Static Analyzer¶

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Undefined Behavior Sanitizer (UBSan)¶

Python Binding Changes¶

The following methods have been added:

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