Fix type instability in logdet(::Matrix{Complex64})

Ref: #10188

1. Adds pi*im in a type stable fashion when there are an odd number of
pivots

2. Uses mod2pi instead of mod(_, 2pi)

base/linalg/lu.jl

@@ -142,9 +142,12 @@ end
 
 function logdet{T<:Complex,S}(A::LU{T,S})
     n = chksquare(A)
-    s = sum(log(diag(A.factors))) + (bool(sum(A.ipiv .!= 1:n) % 2) ? complex(0,pi) : 0)
+    s = sum(log(diag(A.factors)))
+    if bool(sum(A.ipiv .!= 1:n) % 2)
+        s = Complex(real(s), imag(s)+π)
+    end
     r, a = reim(s)
-    a = pi-mod(pi-a,2pi) #Take principal branch with argument (-pi,pi]
+    a = π-mod2pi(π-a) #Take principal branch with argument (-pi,pi]
     complex(r,a)
 end
 

test/runtests.jl

@@ -34,7 +34,7 @@ end
 if "linalg" in tests
     # specifically selected case
     filter!(x -> x != "linalg", tests)
-    prepend!(tests, ["linalg1", "linalg2", "linalg3", "linalg4", "linalg/lapack", "linalg/triangular", "linalg/tridiag", "linalg/pinv", "linalg/givens"])
+    prepend!(tests, ["linalg1", "linalg2", "linalg3", "linalg4", "linalg/lapack", "linalg/triangular", "linalg/tridiag", "linalg/pinv", "linalg/givens", "linalg/lu"])
 end
 
 net_required_for = ["socket", "parallel"]