Port SequenceEqual to crossplat Vectors, optimize vector compare on x64

[EgorBo]

This PR does:

1. Ports SequenceEqual to use cross-plat vectors
2. Optimizes it for arm64 for <16 elements (the path to handle them was guarded with Sse2.IsSupported for some reason)
3. Optimizes vec1 == vec2 with xor+vptest if available:

boolTest(Vector128<int>v1,Vector128<int>v2)=>v1==v2;boolTest(Vector256<int>v1,Vector256<int>v2)=>v1==v2;

codegen diff:

; Method Proga:Test
G_M56888_IG01:
vzeroupper G_M56888_IG02:
vmovupd xmm0, xmmword ptr [rdx]
- vpcmpeqd xmm0, xmm0, xmmword ptr [r8]- vpmovmskb eax, xmm0- cmp eax, 0xFFFF+ vpxor xmm0, xmm0, xmmword ptr [r8]+ vptest xmm0, xmm0
sete al
movzx rax, al
G_M56888_IG03:
ret -; Total bytes of code: 28+; Total bytes of code: 24
; Method Proga:Test
G_M5176_IG01:
vzeroupper G_M5176_IG02:
vmovupd ymm0, ymmword ptr[rdx]
- vpcmpeqd ymm0, ymm0, ymmword ptr[r8]- vpmovmskb eax, ymm0- cmp eax, -1+ vpxor ymm0, ymm0, ymmword ptr[r8]+ vptest ymm0, ymm0
sete al
movzx rax, al
G_M5176_IG03:
vzeroupper ret -; Total bytes of code: 29+; Total bytes of code: 27

However, it seems like in some cases/on some CPUs movmsk is faster 🤔

cc @tannergooding

PS: seems like the main loop in SequenceEqual is not properly aligned and hits JCC erratum each iteration

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Issue Details

---

This PR does:

1. Ports SequenceEqual to use cross-plat vectors
2. Optimizes it for arm64 for <16 elements (the path to handle them was guarded with Sse2.IsSupported for some reason)
3. Optimizes vec == vec with xor+vptest if available:

boolTest(Vector128<int>v1,Vector128<int>v2)=>v1==v2;boolTest(Vector256<int>v1,Vector256<int>v2)=>v1==v2;

codegen diff:

; Method Proga:Test
G_M56888_IG01:
vzeroupper G_M56888_IG02:
vmovupd xmm0, xmmword ptr [rdx]
- vpcmpeqd xmm0, xmm0, xmmword ptr [r8]- vpmovmskb eax, xmm0- cmp eax, 0xFFFF+ vpxor xmm0, xmm0, xmmword ptr [r8]+ vptest xmm0, xmm0
sete al
movzx rax, al
G_M56888_IG03:
ret -; Total bytes of code: 28+; Total bytes of code: 24
; Method Proga:Test
G_M5176_IG01:
vzeroupper G_M5176_IG02:
vmovupd ymm0, ymmword ptr[rdx]
- vpcmpeqd ymm0, ymm0, ymmword ptr[r8]- vpmovmskb eax, ymm0- cmp eax, -1+ vpxor ymm0, ymm0, ymmword ptr[r8]+ vptest ymm0, ymm0
sete al
movzx rax, al
G_M5176_IG03:
vzeroupper ret -; Total bytes of code: 29+; Total bytes of code: 27

However, it seems like in some cases/on some CPUs movmsk is faster 🤔

cc @tannergooding

Author:	EgorBo
Assignees:	EgorBo
Labels:	area-CodeGen-coreclr
Milestone:	-

[tannergooding]

LGTM.