Re: [Xen-devel] [PATCH] x86/HVM: slightly improve hvm_mmio_{first, last}_byte()

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 26 April 2016 09:28
> To: xen-devel
> Cc: Paul Durrant; Wei Liu
> Subject: [PATCH] x86/HVM: slightly improve hvm_mmio_{first,last}_byte()
> 
> EFLAGS.DF can be assumed to be usually clear, so unlikely()-annotate
> the conditionals accordingly.
> 
> Also prefer latching p->size (used twice) into a local variable, at

Well, it should only be used once since only one of the expressions should be 
evaluated.

> once making it unnecessary for the reader to be sure expressions get
> evaluated left to right (operand promotion would yield a different
> result if p->addr + p->size - 1 was evaluted right to left).

Would that not be cured by replacing 1 with 1ul?

  Paul

> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> --- a/xen/include/asm-x86/hvm/io.h
> +++ b/xen/include/asm-x86/hvm/io.h
> @@ -44,18 +44,18 @@ struct hvm_mmio_ops {
> 
>  static inline paddr_t hvm_mmio_first_byte(const ioreq_t *p)
>  {
> -    return p->df ?
> +    return unlikely(p->df) ?
>             p->addr - (p->count - 1ul) * p->size :
>             p->addr;
>  }
> 
>  static inline paddr_t hvm_mmio_last_byte(const ioreq_t *p)
>  {
> -    unsigned long count = p->count;
> +    unsigned long size = p->size;
> 
> -    return p->df ?
> -           p->addr + p->size - 1:
> -           p->addr + (count * p->size) - 1;
> +    return unlikely(p->df) ?
> +           p->addr + size - 1:
> +           p->addr + (p->count * size) - 1;
>  }
> 
>  typedef int (*portio_action_t)(
> 
> 


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