RFC: Change uint8 to uint16_t for _num_regs

[Aleksey Shipilev]

On 4/1/21 7:20 AM, Leslie Zhai wrote:
> Patch:
> 
> diff --git a/hotspot/src/share/vm/opto/chaitin.hpp
> b/hotspot/src/share/vm/opto/chaitin.hpp
> index de6d443..94f66b8 100644
> --- a/hotspot/src/share/vm/opto/chaitin.hpp
> +++ b/hotspot/src/share/vm/opto/chaitin.hpp
> @@ -136,7 +136,7 @@ public:
> 
>      // Number of registers this live range uses when it colors
>    private:
> -  uint8 _num_regs;              // 2 for Longs and Doubles, 1 for all else
> +  uint16_t _num_regs;           // 2 for Longs and Doubles, 1 for all else
>                                    // except _num_regs is kill count for
> fat_proj
>    public:
>      int num_regs() const { return _num_regs; }

Looks to me it was changed to uint16_t in JDK 9 by "8076276: Add support for AVX512"
   https://bugs.openjdk.java.net/browse/JDK-8076276

Note that patch also changed:
  -  uint8_t _reg_pressure;
  +  uint16_t _reg_pressure;

 From reading the uses of these fields, I think these are more or less safe to widen.

-- 
Thanks,
-Aleksey