Unalias source from dest in copytrito (#54474)

(cherry picked from commit 72d644f)

Author: jishnub

stdlib/LinearAlgebra/src/generic.jl

@@ -1935,6 +1935,7 @@ function copytrito!(B::AbstractMatrix, A::AbstractMatrix, uplo::AbstractChar)
     m,n = size(A)
     m1,n1 = size(B)
     (m1 < m || n1 < n) && throw(DimensionMismatch(lazy"B of size ($m1,$n1) should have at least the same number of rows and columns than A of size ($m,$n)"))
+    A = Base.unalias(B, A)
     if uplo == 'U'
         for j=1:n
             for i=1:min(j,m)

stdlib/LinearAlgebra/test/generic.jl

@@ -654,6 +654,14 @@ end
         C = uplo == 'L' ? tril(A) : triu(A)
         @test B ≈ C
     end
+    @testset "aliasing" begin
+        M = Matrix(reshape(1:36, 6, 6))
+        A = view(M, 1:5, 1:5)
+        A2 = Matrix(A)
+        B = view(M, 2:6, 2:6)
+        copytrito!(B, A, 'U')
+        @test UpperTriangular(B) == UpperTriangular(A2)
+    end
 end
 
 @testset "immutable arrays" begin