RFR: 8256054: C2: Floating-point min/max operations on vectors intermittently produce wrong results for NaN values

[Dean Long]

On Mon, 9 Nov 2020 14:57:09 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> Floating-point min/max operations on vectors intermittently produce wrong results for NaN values.
> 
> The problem boils down to a missing "TEMP dst" declaration on AVX512-related AD instruction. Without it`dst` vector register may match one of the input registers and it breaks the computation since it assumes all the used registers are different.
> 
> The fix adds missing effect and also introduces additional asserts to catch similar problems in the future.  
> 
> Testing:
> - [x] jdk/incubator/vector w/ -XX:+DeoptimizeALot on AVX512-capable hardware
> - [x] hs-precheckin-comp, hs-tier1, hs-tier2
> 
> Thanks!

Marked as reviewed by dlong (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/1128