RFR (M) 8222074: Enhance auto vectorization for x86

[Viswanathan, Sandhya]

Hi Bernard,

One could add TEMP dst in effect() to let the register allocator know that dst needs to be different from src.

Best Regards,
Sandhya


-----Original Message-----
From: B. Blaser [mailto:bsrbnd at gmail.com] 
Sent: Wednesday, April 10, 2019 4:10 AM
To: Viswanathan, Sandhya <sandhya.viswanathan at intel.com>
Cc: Vladimir Kozlov <vladimir.kozlov at oracle.com>; hotspot-compiler-dev at openjdk.java.net
Subject: Re: RFR (M) 8222074: Enhance auto vectorization for x86

Hi Sandhya and Vladimir K.,

On Wed, 10 Apr 2019 at 03:06, Viswanathan, Sandhya <sandhya.viswanathan at intel.com> wrote:
>
> Hi Vladimir,
>
> Yes, I missed the question below:
> >> There are cases where we can use less `TEMP tmp` registers by using 'dst' register like in mul4B_reg(). Is it intentional to not use 'dst' there?
>
> No it is not intentional, we can use the dst register in those cases and reduced the tmps.

I guess we have to be careful using $dst instead of $tmp registers as the allocator sometimes provides identical $src & $dst. Also, I'm not sure this would be possible in the case of mul4B_reg():

7349   format %{"pmovsxbw  $tmp,$src1\n\t"
7350            "pmovsxbw  $tmp2,$src2\n\t"

I believe this couldn't work if you use $dst instead of $tmp and $dst = $src2, what do you think?

Thanks,
Bernard