Major New Features¶

• The diagnose_if attribute has been added to clang. This attribute allows clang to emit a warning or error if a function call meets one or more user-specified conditions.

• Enhanced devirtualization with -fstrict-vtable-pointers. Clang devirtualizes across different basic blocks, like loops:

  struct A {
      virtual void foo();
  };
  void indirect(A &a, int n) {
      for (int i = 0 ; i < n; i++)
          a.foo();
  }
  void test(int n) {
      A a;
      indirect(a, n);
  }
  

Improvements to ThinLTO (-flto=thin)¶

• Integration with profile data (PGO). When available, profile data enables more accurate function importing decisions, as well as cross-module indirect call promotion.
• Significant build-time and binary-size improvements when compiling with debug info (-g).

New Compiler Flags¶

• The option -Og has been added to optimize the debugging experience. For now, this option is exactly the same as -O1. However, in the future, some other optimizations might be enabled or disabled.
• The option -MJ has been added to simplify adding JSON compilation database output into existing build systems.

OpenCL C Language Changes in Clang¶

The following bugs in the OpenCL header have been fixed:

• Added missing overloadable and convergent attributes.
• Removed some erroneous extra native_* functions.

The following bugs in the generation of metadata have been fixed:

• Corrected the SPIR version depending on the OpenCL version.
• Source level address spaces are taken from the SPIR specification.
• Image types now contain no access qualifier.

The following bugs in the AMD target have been fixed:

• Corrected the bitwidth of size_t and NULL pointer value with respect to address spaces.
• Added cl_khr_subgroups, cl_amd_media_ops and cl_amd_media_ops2 extensions.
• Added cl-denorms-are-zero support.
• Changed address spaces for image objects to be constant.
• Added little-endian.

The following bugs in OpenCL 2.0 have been fixed:

• Fixed pipe builtin function return type, added extra argument to generated IR intrinsics to propagate size and alignment information of the pipe packed type.
• Improved pipe type to accommodate access qualifiers.
• Added correct address space to the ObjC block generation and enqueue_kernel prototype.
• Improved handling of integer parameters of enqueue_kernel prototype. We now allow size_t instead of int for specifying block parameter sizes.
• Allow using NULL (aka CLK_NULL_QUEUE) with queue_t.

Improved the following diagnostics:

• Disallow address spaces other than global for kernel pointer parameters.
• Correct the use of half type argument and pointer assignment with dereferencing.
• Disallow variadic arguments in functions and blocks.
• Allow partial initializer for array and struct.

Some changes to OpenCL extensions have been made:

• Added cl_khr_mipmap_image.

• Added -cl-ext flag to allow overwriting supported extensions otherwise set by the target compiled for (Example: -cl-ext=-all,+cl_khr_fp16).

• New types and functions can now be flexibly added to extensions using the following pragmas instead of modifying the Clang source code:

  #pragma OPENCL EXTENSION the_new_extension_name : begin
  // declare types and functions associated with the extension here
  #pragma OPENCL EXTENSION the_new_extension_name : end
  

Miscellaneous changes:

• Fix __builtin_astype to cast between different address space objects.
• Allow using opencl_unroll_hint with earlier OpenCL versions than 2.0.
• Improved handling of floating point literal to default to single precision if fp64 extension is not enabled.
• Refactor sampler_t implementation to simplify initializer representation which is now handled as a compiler builtin function with an integer value passed into it.
• Change fake address space map to use the SPIR convention.
• Added the OpenCL manual to Clang documentation.

Static Analyzer¶

With the option --show-description, scan-build’s list of defects will also show the description of the defects.

The analyzer now provides better support of code that uses gtest.

Several new checks were added:

• The analyzer warns when virtual calls are made from constructors or destructors. This check is off by default but can be enabled by passing the following command to scan-build: -enable-checker optin.cplusplus.VirtualCall.
• The analyzer checks for synthesized copy properties of mutable types in Objective C, such as NSMutableArray. Calling the setter for these properties will store an immutable copy of the value.
• The analyzer checks for calls to dispatch_once() that use an Objective-C instance variable as the predicate. Using an instance variable as a predicate may result in the passed-in block being executed multiple times or not at all. These calls should be rewritten either to use a lock or to store the predicate in a global or static variable.
• The analyzer checks for unintended comparisons of NSNumber, CFNumberRef, and other Cocoa number objects to scalar values.