Hello,

I encountered this in one of my applications. All these tests are with 1 thread.

Here is a MWE:

```
function filla!(a)
for i2 in 1:size(a,2)
@simd for i1 in 1:size(a,1)
@inbounds a[i1,i2]=i1/i2
end
end
end
function fillat!(a)
Threads.@thread for i2 in 1:size(a,2)
@simd for i1 in 1:size(a,1)
@inbounds a[i1,i2]=i1/i2
end
end
end
[(n=10^i;a1=rand(n,n);a2=rand(n,n);t1=@elapsed filla!(a1);t2=@elapsed fillat!(a2);(t1,t2/t1,vecnorm(a2-a1))) for i=1:4]
```

Gives:

```
(5.61e-7, 3201.8128342245986, 0.0)
(3.2746e-5, 1.9932816221828618, 0.0)
(0.003361921, 1.9781815218144627, 0.0)
(0.335100165, 1.9968342778941932, 0.0)
```

Now remove `@simd`

from `fillat!`

:

```
(6.66e-7, 2642.8468468468473, 0.0)
(3.2544e-5, 1.0197885939036382, 0.0)
(0.003398881, 0.9780936725940096, 0.0)
(0.335104378, 0.9972122536698103, 0.0)
```

Without `@simd`

there is no overhead for `@thread`

which is great, but with `@simd`

a factor of 2 regression (can be worse on more complicated examples).

```
Julia Version 0.7.0-alpha.0
Commit 22590d5 (2018-05-31 00:07 UTC)
Platform Info:
OS: Linux (x86_64-suse-linux)
CPU: Intel(R) Xeon(R) CPU E5-2670 0 @ 2.60GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-6.0.0 (ORCJIT, sandybridge)
Environment:
JULIA_NUM_THREADS = 1
```

On `julia 0.6.2`

there is no such regression.

Is this expected/documented? Is it worth reporting?

Thanks!