RFR: 8285868: x86 intrinsics for floating point method isInfinite [v9]

[Srinivas Vamsi Parasa]

On Wed, 1 Jun 2022 16:14:37 GMT, Srinivas Vamsi Parasa <duke at openjdk.java.net> wrote:

> @vamsi-parasa can you show difference in generated code for `DoubleClassCheck.testIsFiniteCMov ` for example? Or may be for all of them (for DoubleClassCheck). I am fine with intrinsifying only `isInfinite()` but would like to see code for the record.

Hi Vladimir (@vnkozlov), please see the generated code below.

`isInfinite()` intrinsic is faster because the baseline produces` 2 vucomisd` instructions to compare with positive and negative infinity whereas the intrinsic generates only one `vfpclasssd` instruction as seen below:

**DoubleClassCheck.testIsInfiniteBranch (baseline)**
                                                                 

vucomisd -0xad(%rip),%xmm0         
jp     0x00007fe1aced1f31
je     0x00007fe1aced1f3d          
vucomisd -0xb1(%rip),%xmm0      
jp     0x00007fe1aced1ee0
jne    0x00007fe1aced1ee0

**DoubleClassCheck.testIsInfiniteBranch (intrinsic/vfpclasssd)**

vfpclasssd $0x18,%xmm0,%k7
kmovb  %k7,%edi
test   %edi,%edi
je     0x00007f1270c167e0 


-------------------------
However, in the case of` isFinite() `and `isNan()`, only `1 vucomisd` is generated and is faster for `Cmov` and` branch/call` tests as seen below

**DoubleClassCheck.testIsFiniteCmov (baseline)**
 
```    
vucomisd %xmm0,%xmm1
mov    $0x9,%ecx
cmovb  %r8d,%ecx


**DoubleClassCheck.testIsFiniteCmov (intrinsci/vfpclasssd)**


vfpclasssd $0x99,%xmm2,%k7
kmovb  %k7,%r11d
xor    $0x1,%r11d
test   %r11d,%r11d
mov    $0x7,%r11d
cmovne %r8d,%r11d

-------------------------------------------------------------------------

**DoubleClassCheck.testIsNaNCmov(baseline)**
 

vucomisd %xmm0,%xmm0
jp     0x00007f0a4d1425fb           
movl   $0x7,0x10(%rcx,%rax,4) 


**DoubleClassCheck.testIsNaNCmov (intrinsic/vfpclasssd)**
 

vfpclasssd $0x81,%xmm0,%k7
kmovb  %k7,%r8d                    
test   %r8d,%r8d
jne  0x00007f7fa0c50f43    
movl   $0x7,0x10(%r10,%rdx,4) 
```  

Please let me know if further data is needed. 

Thanks,
Vamsi

-------------

PR: https://git.openjdk.java.net/jdk/pull/8459