fix bit_map! with aliasing (#50781)

fixes #50780 caused by #47013.

Author: oscardssmith

base/bitarray.jl

@@ -1791,9 +1791,10 @@ function bit_map!(f::F, dest::BitArray, A::BitArray) where F
     dest_last = destc[len_Ac]
     _msk = _msk_end(A)
     # first zero out the bits mask is going to change
-    destc[len_Ac] = (dest_last & (~_msk))
     # then update bits by `or`ing with a masked RHS
-    destc[len_Ac] |= f(Ac[len_Ac]) & _msk
+    # DO NOT SEPARATE ONTO TO LINES.
+    # Otherwise there will be bugs when Ac aliases destc
+    destc[len_Ac] = (dest_last & (~_msk)) | f(Ac[len_Ac]) & _msk
     dest
 end
 function bit_map!(f::F, dest::BitArray, A::BitArray, B::BitArray) where F
@@ -1812,9 +1813,10 @@ function bit_map!(f::F, dest::BitArray, A::BitArray, B::BitArray) where F
     dest_last = destc[len_Ac]
     _msk = _msk_end(min_bitlen)
     # first zero out the bits mask is going to change
-    destc[len_Ac] = (dest_last & ~(_msk))
     # then update bits by `or`ing with a masked RHS
-    destc[len_Ac] |= f(Ac[end], Bc[end]) & _msk
+    # DO NOT SEPARATE ONTO TO LINES.
+    # Otherwise there will be bugs when Ac or Bc aliases destc
+    destc[len_Ac] = (dest_last & ~(_msk)) | f(Ac[end], Bc[end]) & _msk
     dest
 end
 

test/bitarray.jl

@@ -1539,6 +1539,21 @@ timesofar("reductions")
             end
         end
     end
+    @testset "Issue #50780, map! bitarray map! where dest aliases source" begin
+        a = BitVector([1,0])
+        b = map(!, a)
+        map!(!, a, a) # a .= !.a
+        @test a == b == BitVector([0,1])
+
+        a = BitVector([1,0])
+        c = map(|, a, b)
+        map!(|, a, a, b)
+        @test c == a == BitVector([1, 1])
+
+        a = BitVector([1,0])
+        map!(|, b, a, b)
+        @test c == b == BitVector([1, 1])
+    end
 end
 
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