2023-07-18 07:23:32

by Huacai Chen

Subject: [PATCH] LoongArch: Cleanup __builtin_constant_p() checking for cpu_has_*

In current configuration, cpu_has_lsx and cpu_has_lasx are impossible
constants. So cleanup the __builtin_constant_p() checking to reduce the
complexity.

Signed-off-by: Huacai Chen <[email protected]>
---
arch/loongarch/include/asm/fpu.h | 11 +++--------
1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/arch/loongarch/include/asm/fpu.h b/arch/loongarch/include/asm/fpu.h
index e4193d637f66..f02f4a0d0d64 100644
--- a/arch/loongarch/include/asm/fpu.h
+++ b/arch/loongarch/include/asm/fpu.h
@@ -218,12 +218,7 @@ static inline void restore_lsx(struct task_struct *t)

static inline void init_lsx_upper(void)
{
- /*
- * Check cpu_has_lsx only if it's a constant. This will allow the
- * compiler to optimise out code for CPUs without LSX without adding
- * an extra redundant check for CPUs with LSX.
- */
- if (__builtin_constant_p(cpu_has_lsx) && !cpu_has_lsx)
+ if (!cpu_has_lsx)
return;

_init_lsx_upper();
@@ -294,7 +289,7 @@ static inline void restore_lasx_upper(struct task_struct *t) {}

static inline int thread_lsx_context_live(void)
{
- if (__builtin_constant_p(cpu_has_lsx) && !cpu_has_lsx)
+ if (!cpu_has_lsx)
return 0;

return test_thread_flag(TIF_LSX_CTX_LIVE);
@@ -302,7 +297,7 @@ static inline int thread_lsx_context_live(void)

static inline int thread_lasx_context_live(void)
{
- if (__builtin_constant_p(cpu_has_lasx) && !cpu_has_lasx)
+ if (!cpu_has_lasx)
return 0;

return test_thread_flag(TIF_LASX_CTX_LIVE);
--
2.39.3

2023-07-18 07:59:00

by WANG Xuerui

Subject: Re: [PATCH] LoongArch: Cleanup __builtin_constant_p() checking for cpu_has_*

On 2023/7/18 14:48, Huacai Chen wrote:
> In current configuration, cpu_has_lsx and cpu_has_lasx are impossible
> constants. So cleanup the __builtin_constant_p() checking to reduce the

"cannot be constants"? "impossible constants" sounds like a compile-time
error to me.

> complexity.
>
> Signed-off-by: Huacai Chen <[email protected]>
> ---
> arch/loongarch/include/asm/fpu.h | 11 +++--------
> 1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/fpu.h b/arch/loongarch/include/asm/fpu.h
> index e4193d637f66..f02f4a0d0d64 100644
> --- a/arch/loongarch/include/asm/fpu.h
> +++ b/arch/loongarch/include/asm/fpu.h
> @@ -218,12 +218,7 @@ static inline void restore_lsx(struct task_struct *t)
>
> static inline void init_lsx_upper(void)
> {
> - /*
> - * Check cpu_has_lsx only if it's a constant. This will allow the
> - * compiler to optimise out code for CPUs without LSX without adding
> - * an extra redundant check for CPUs with LSX.
> - */
> - if (__builtin_constant_p(cpu_has_lsx) && !cpu_has_lsx)
> + if (!cpu_has_lsx)
> return;
>
> _init_lsx_upper();
> @@ -294,7 +289,7 @@ static inline void restore_lasx_upper(struct task_struct *t) {}
>
> static inline int thread_lsx_context_live(void)
> {
> - if (__builtin_constant_p(cpu_has_lsx) && !cpu_has_lsx)
> + if (!cpu_has_lsx)
> return 0;
>
> return test_thread_flag(TIF_LSX_CTX_LIVE);
> @@ -302,7 +297,7 @@ static inline int thread_lsx_context_live(void)
>
> static inline int thread_lasx_context_live(void)
> {
> - if (__builtin_constant_p(cpu_has_lasx) && !cpu_has_lasx)
> + if (!cpu_has_lasx)
> return 0;
>
> return test_thread_flag(TIF_LASX_CTX_LIVE);

For the foreseeable future, the changes seem appropriate to me. FWIW the
LoongArch kernel would stay as generic as possible so I expect the
various predicates to almost never exist as constants.

Reviewed-by: WANG Xuerui <[email protected]>

--
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/

2023-07-18 08:54:50

by Huacai Chen

Subject: Re: [PATCH] LoongArch: Cleanup __builtin_constant_p() checking for cpu_has_*

On Tue, Jul 18, 2023 at 3:35 PM WANG Xuerui <[email protected]> wrote:
>
> On 2023/7/18 14:48, Huacai Chen wrote:
> > In current configuration, cpu_has_lsx and cpu_has_lasx are impossible
> > constants. So cleanup the __builtin_constant_p() checking to reduce the
>
> "cannot be constants"? "impossible constants" sounds like a compile-time
> error to me.
OK, thanks.

Huacai
>
> > complexity.
> >
> > Signed-off-by: Huacai Chen <[email protected]>
> > ---
> > arch/loongarch/include/asm/fpu.h | 11 +++--------
> > 1 file changed, 3 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/loongarch/include/asm/fpu.h b/arch/loongarch/include/asm/fpu.h
> > index e4193d637f66..f02f4a0d0d64 100644
> > --- a/arch/loongarch/include/asm/fpu.h
> > +++ b/arch/loongarch/include/asm/fpu.h
> > @@ -218,12 +218,7 @@ static inline void restore_lsx(struct task_struct *t)
> >
> > static inline void init_lsx_upper(void)
> > {
> > - /*
> > - * Check cpu_has_lsx only if it's a constant. This will allow the
> > - * compiler to optimise out code for CPUs without LSX without adding
> > - * an extra redundant check for CPUs with LSX.
> > - */
> > - if (__builtin_constant_p(cpu_has_lsx) && !cpu_has_lsx)
> > + if (!cpu_has_lsx)
> > return;
> >
> > _init_lsx_upper();
> > @@ -294,7 +289,7 @@ static inline void restore_lasx_upper(struct task_struct *t) {}
> >
> > static inline int thread_lsx_context_live(void)
> > {
> > - if (__builtin_constant_p(cpu_has_lsx) && !cpu_has_lsx)
> > + if (!cpu_has_lsx)
> > return 0;
> >
> > return test_thread_flag(TIF_LSX_CTX_LIVE);
> > @@ -302,7 +297,7 @@ static inline int thread_lsx_context_live(void)
> >
> > static inline int thread_lasx_context_live(void)
> > {
> > - if (__builtin_constant_p(cpu_has_lasx) && !cpu_has_lasx)
> > + if (!cpu_has_lasx)
> > return 0;
> >
> > return test_thread_flag(TIF_LASX_CTX_LIVE);
>
> For the foreseeable future, the changes seem appropriate to me. FWIW the
> LoongArch kernel would stay as generic as possible so I expect the
> various predicates to almost never exist as constants.
>
> Reviewed-by: WANG Xuerui <[email protected]>
>
> --
> WANG "xen0n" Xuerui
>
> Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/
>