arm64: atomics: lse: define ANDs in terms of ANDNOTs

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 <mark.rutland@arm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20211210151410.2782645-4-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

0 files changed, 0 insertions, 0 deletions