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Mark Rutland
5e9e43c987
The FEAT_LSE atomic instructions include atomic bit-clear instructions
(`ldclr*` and `stclr*`) which can be used to directly implement ANDNOT
operations. Each AND op is implemented as a copy of the corresponding
ANDNOT op with a leading `mvn` instruction to apply a bitwise NOT to the
`i` argument.
As the compiler has no visibility of the `mvn`, this leads to less than
optimal code generation when generating `i` into a register. For
example, __lse_atomic_fetch_and(0xf, v) can be compiled to:
mov w1, #0xf
mvn w1, w1
ldclral w1, w1, [x2]
This patch improves this by replacing the `mvn` with NOT in C before the
inline assembly block, e.g.
i = ~i;
This allows the compiler to generate `i` into a register more optimally,
e.g.
mov w1, #0xfffffff0
ldclral w1, w1, [x2]
With this change the assembly for each AND op is identical to the
corresponding ANDNOT op (including barriers and clobbers), so I've
removed the inline assembly and rewritten each AND op in terms of the
corresponding ANDNOT op, e.g.
| static inline void __lse_atomic_and(int i, atomic_t *v)
| {
| return __lse_atomic_andnot(~i, v);
| }
This is intended as an optimization and cleanup.
There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Will Deacon <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.