12.0.1:
Non-comprehensive list of changes in this release
The builtin intrinsics __builtin_bitreverse8, __builtin_bitreverse16, __builtin_bitreverse32 and __builtin_bitreverse64 may now be used within constant expressions.
The builtin intrinsics __builtin_rotateleft8, __builtin_rotateleft16, __builtin_rotateleft32 and __builtin_rotateleft64 may now be used within constant expressions.
The builtin intrinsics __builtin_rotateright8, __builtin_rotateright16, __builtin_rotateright32 and __builtin_rotateright64 may now be used within constant expressions.
New Compiler Flags
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AArch64 options -moutline-atomics, -mno-outline-atomics to enable and disable calls to helper functions implementing atomic operations. These out-of-line helpers like ‘__aarch64_cas8_relax’ will detect at runtime AArch64 Large System Extensions (LSE) availability and either use their atomic instructions, or falls back to LL/SC loop. These options do not apply if the compilation target supports LSE. Atomic instructions are used directly in that case. The option’s behaviour mirrors GCC, the helpers are implemented both in compiler-rt and libgcc.
New option -fbinutils-version= specifies the targeted binutils version. For example, -fbinutils-version=2.35 means compatibility with GNU as/ld before 2.35 is not needed: new features can be used and there is no need to work around old GNU as/ld bugs.
Deprecated Compiler Flags
The following options are deprecated and ignored. They will be removed in future versions of Clang.
The clang-cl /fallback flag, which made clang-cl invoke Microsoft Visual C++ on files it couldn’t compile itself, has been deprecated. It will be removed in Clang 13.
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Modified Compiler Flags
On ELF, -gz now defaults to -gz=zlib with the integrated assembler. It produces SHF_COMPRESSED style compression of debug information. GNU binutils 2.26 or newer, or lld is required to link produced object files. Use -gz=zlib-gnu to get the old behavior.
Now that this pointers are tagged with nonnull and dereferenceable(N), -fno-delete-null-pointer-checks has gained the power to remove the nonnull attribute on this for configurations that need it to be nullable.
-gsplit-dwarf no longer implies -g2.
-fasynchronous-unwind-tables is now the default on Linux AArch64/PowerPC. This behavior matches newer GCC. (D91760) (D92054)
Support has been added for the following processors (command-line identifiers in parentheses):
Arm Cortex-A78C (cortex-a78c).
Arm Cortex-R82 (cortex-r82).
Arm Neoverse V1 (neoverse-v1).
Arm Neoverse N2 (neoverse-n2).
Fujitsu A64FX (a64fx).
For example, to select architecture support and tuning for Neoverse-V1 based systems, use -mcpu=neoverse-v1.
Removed Compiler Flags
The following options no longer exist.
clang-cl’s /Zd flag no longer exist. But -gline-tables-only still exists and does the same thing.
New Pragmas in Clang
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Modified Pragmas in Clang
The “#pragma clang loop vectorize_width” has been extended to support an optional ‘fixed|scalable’ argument, which can be used to indicate that the compiler should use fixed-width or scalable vectorization. Fixed-width is assumed by default.
Scalable or vector length agnostic vectorization is an experimental feature for targets that support scalable vectors. For more information please refer to the Clang Language Extensions documentation.
Attribute Changes in Clang
Added support for the C++20 likelihood attributes [[likely]] and [[unlikely]]. As an extension they can be used in C++11 and newer. This extension is enabled by default.
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