Re: [PATCH] m68k: One function call less in cf_tlb_miss()

[Geert Uytterhoeven]

Hi Markus,

On Sat, Jul 6, 2019 at 1:57 AM Finn Thain  wrote:
> On Fri, 5 Jul 2019, Markus Elfring wrote:
> > From: Markus Elfring 
> > Date: Fri, 5 Jul 2019 17:11:37 +0200
> >
> > Avoid an extra function call
> > by using a ternary operator instead of a conditional statement for a
> > setting selection.

Have you looked at the actual assembler output generated by the compiler?

> > This issue was detected by using the Coccinelle software.
> >
> > Signed-off-by: Markus Elfring 
> > ---
> >  arch/m68k/mm/mcfmmu.c | 10 --
> >  1 file changed, 4 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/m68k/mm/mcfmmu.c b/arch/m68k/mm/mcfmmu.c
> > index 6cb1e41d58d0..02fc0778028e 100644
> > --- a/arch/m68k/mm/mcfmmu.c
> > +++ b/arch/m68k/mm/mcfmmu.c
> > @@ -146,12 +146,10 @@ int cf_tlb_miss(struct pt_regs *regs, int write, int 
> > dtlb, int extension_word)
> >
> >   mmu_write(MMUDR, (pte_val(*pte) & PAGE_MASK) |
> >   ((pte->pte) & CF_PAGE_MMUDR_MASK) | MMUDR_SZ_8KB | MMUDR_X);
> > -
> > - if (dtlb)
> > - mmu_write(MMUOR, MMUOR_ACC | MMUOR_UAA);
> > - else
> > - mmu_write(MMUOR, MMUOR_ITLB | MMUOR_ACC | MMUOR_UAA);
> > -
> > + mmu_write(MMUOR,
> > +   dtlb
> > +   ? MMUOR_ACC | MMUOR_UAA
> > +   : MMUOR_ITLB | MMUOR_ACC | MMUOR_UAA);

While the ternary operator can be useful for short expressions, it can
also lead to hard-to-read code.  IMHO the latter is the case here
(hint: the expression needs 3 lines).

> If you are trying to avoid redundancy, why not finish the job?
>
> + mmu_write(MMUOR, (dtlb ? 0 : MMUOR_ITLB) | MMUOR_ACC | MMUOR_UAA);

Thanks Finn, much better!

Gr{oetje,eeting}s,

Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds

Re: [PATCH] m68k: One function call less in cf_tlb_miss()

[Finn Thain]

On Fri, 5 Jul 2019, Markus Elfring wrote:

> From: Markus Elfring 
> Date: Fri, 5 Jul 2019 17:11:37 +0200
> 
> Avoid an extra function call 

Not really. You've avoided an extra statement.

> by using a ternary operator instead of a conditional statement for a 
> setting selection.
> 
> This issue was detected by using the Coccinelle software.
> 
> Signed-off-by: Markus Elfring 
> ---
>  arch/m68k/mm/mcfmmu.c | 10 --
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/m68k/mm/mcfmmu.c b/arch/m68k/mm/mcfmmu.c
> index 6cb1e41d58d0..02fc0778028e 100644
> --- a/arch/m68k/mm/mcfmmu.c
> +++ b/arch/m68k/mm/mcfmmu.c
> @@ -146,12 +146,10 @@ int cf_tlb_miss(struct pt_regs *regs, int write, int 
> dtlb, int extension_word)
> 
>   mmu_write(MMUDR, (pte_val(*pte) & PAGE_MASK) |
>   ((pte->pte) & CF_PAGE_MMUDR_MASK) | MMUDR_SZ_8KB | MMUDR_X);
> -
> - if (dtlb)
> - mmu_write(MMUOR, MMUOR_ACC | MMUOR_UAA);
> - else
> - mmu_write(MMUOR, MMUOR_ITLB | MMUOR_ACC | MMUOR_UAA);
> -
> + mmu_write(MMUOR,
> +   dtlb
> +   ? MMUOR_ACC | MMUOR_UAA
> +   : MMUOR_ITLB | MMUOR_ACC | MMUOR_UAA);

If you are trying to avoid redundancy, why not finish the job?

+ mmu_write(MMUOR, (dtlb ? 0 : MMUOR_ITLB) | MMUOR_ACC | MMUOR_UAA);

-- 

>   local_irq_restore(flags);
>   return 0;
>  }
> --
> 2.22.0
> 
> 

[PATCH] m68k: One function call less in cf_tlb_miss()

[Markus Elfring]

From: Markus Elfring 
Date: Fri, 5 Jul 2019 17:11:37 +0200

Avoid an extra function call by using a ternary operator instead of
a conditional statement for a setting selection.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring 
---
 arch/m68k/mm/mcfmmu.c | 10 --
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/m68k/mm/mcfmmu.c b/arch/m68k/mm/mcfmmu.c
index 6cb1e41d58d0..02fc0778028e 100644
--- a/arch/m68k/mm/mcfmmu.c
+++ b/arch/m68k/mm/mcfmmu.c
@@ -146,12 +146,10 @@ int cf_tlb_miss(struct pt_regs *regs, int write, int 
dtlb, int extension_word)

mmu_write(MMUDR, (pte_val(*pte) & PAGE_MASK) |
((pte->pte) & CF_PAGE_MMUDR_MASK) | MMUDR_SZ_8KB | MMUDR_X);
-
-   if (dtlb)
-   mmu_write(MMUOR, MMUOR_ACC | MMUOR_UAA);
-   else
-   mmu_write(MMUOR, MMUOR_ITLB | MMUOR_ACC | MMUOR_UAA);
-
+   mmu_write(MMUOR,
+ dtlb
+ ? MMUOR_ACC | MMUOR_UAA
+ : MMUOR_ITLB | MMUOR_ACC | MMUOR_UAA);
local_irq_restore(flags);
return 0;
 }
--
2.22.0