use explicit simd for iszero check on partials

[KristofferC]

Now:

julia> code_native(ForwardDiff.iszero_tuple, Tuple{NTuple{4, Float64}}; debuginfo=:none) .section __TEXT,__text,regular,pure_instructions vxorpd %xmm0, %xmm0, %xmm0 vcmpneqpd (%rdi), %ymm0, %ymm0 vmovmskpd %ymm0, %eax testb %al, %al sete %alvzeroupper retq nopw %cs:(%rax,%rax)

On master:

julia> code_native(ForwardDiff.iszero_tuple, Tuple{NTuple{4, Float64}}; debuginfo=:none) .section __TEXT,__text,regular,pure_instructions vmovsd (%rdi), %xmm1 ## xmm1 = mem[0],zero vxorpd %xmm0, %xmm0, %xmm0 vucomisd %xmm0, %xmm1jne L46jp L46 vmovsd 8(%rdi), %xmm1 ## xmm1 = mem[0],zero vucomisd %xmm0, %xmm1jne L46jp L46 vmovsd 16(%rdi), %xmm1 ## xmm1 = mem[0],zero vxorpd %xmm0, %xmm0, %xmm0 vucomisd %xmm0, %xmm1jne L46jnp L49L46: xorl %eax, %eax retqL49: vcmpeqsd 24(%rdi), %xmm0, %xmm0vmovq %xmm0, %rax andl$1, %eax retq

[codecov-commenter]

Codecov Report

Merging #559 (4469639) into master (d033d2a) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@ Coverage Diff @@## master #559 +/- ##
==========================================
+ Coverage 84.95% 84.97% +0.01% 
==========================================
Files 9 9 Lines 844 845 +1 ==========================================
+ Hits 717 718 +1 
Misses 127 127 

Impacted Files	Coverage Δ
src/partials.jl	84.48% <100.00%> (+0.13%)	⬆️

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