Improve __acpi_acquire_global_lock by using a temporary variable.
This enables compiler to perform if-conversion and improves generated
code from:
...
72a: d1 ea shr %edx
72c: 83 e1 fc and $0xfffffffc,%ecx
72f: 83 e2 01 and $0x1,%edx
732: 09 ca or %ecx,%edx
734: 83 c2 02 add $0x2,%edx
737: f0 0f b1 17 lock cmpxchg %edx,(%rdi)
73b: 75 e9 jne 726 <__acpi_acquire_global_lock+0x6>
73d: 83 e2 03 and $0x3,%edx
740: 31 c0 xor %eax,%eax
742: 83 fa 03 cmp $0x3,%edx
745: 0f 95 c0 setne %al
748: f7 d8 neg %eax
to:
...
72a: d1 e9 shr %ecx
72c: 83 e2 fc and $0xfffffffc,%edx
72f: 83 e1 01 and $0x1,%ecx
732: 09 ca or %ecx,%edx
734: 83 c2 02 add $0x2,%edx
737: f0 0f b1 17 lock cmpxchg %edx,(%rdi)
73b: 75 e9 jne 726 <__acpi_acquire_global_lock+0x6>
73d: 8d 41 ff lea -0x1(%rcx),%eax
BTW: the compiler could generate:
lea 0x2(%rcx,%rdx,1),%edx
instead of:
or %ecx,%edx
add $0x2,%edx
but unwated conversion from add to or when bits are known to be zero
prevents this improvement. This is GCC PR108477.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
---
v2: Expand return statement.
---
arch/x86/kernel/acpi/boot.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 1c38174b5f01..a08a4a7a03f8 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -1853,13 +1853,18 @@ early_param("acpi_sci", setup_acpi_sci);
int __acpi_acquire_global_lock(unsigned int *lock)
{
- unsigned int old, new;
+ unsigned int old, new, val;
old = READ_ONCE(*lock);
do {
- new = (((old & ~0x3) + 2) + ((old >> 1) & 0x1));
+ val = (old >> 1) & 0x1;
+ new = (old & ~0x3) + 2 + val;
} while (!try_cmpxchg(lock, &old, new));
- return ((new & 0x3) < 3) ? -1 : 0;
+
+ if (val)
+ return 0;
+
+ return -1;
}
int __acpi_release_global_lock(unsigned int *lock)
--
2.39.2
