Fix implementation of mul! for AbstractMatrix and AbstractVector

src/implementations/LinearAlgebra.jl

@@ -298,46 +298,44 @@ function _dim_check(C::AbstractMatrix, A::AbstractMatrix, B::AbstractMatrix)
     return
 end
 
-function _add_mul_array(buffer, C::Vector, A::AbstractMatrix, B::AbstractVector)
-    Astride = size(A, 1)
-    # We need a buffer to hold the intermediate multiplication.
-    @inbounds begin
-        for k in eachindex(B)
-            aoffs = (k - 1) * Astride
-            b = B[k]
-            for i in Base.OneTo(size(A, 1))
-                C[i] = buffered_operate!!(buffer, add_mul, C[i], A[aoffs+i], b)
-            end
-        end
-    end # @inbounds
-    return C
-end
-
-# This is incorrect if `C` is `LinearAlgebra.Symmetric` as we modify twice the
-# same diagonal element.
-function _add_mul_array(buffer, C::Matrix, A::AbstractMatrix, B::AbstractMatrix)
-    @inbounds begin
-        for i in 1:size(A, 1), j in 1:size(B, 2)
-            Ctmp = C[i, j]
-            for k in 1:size(A, 2)
-                Ctmp =
-                    buffered_operate!!(buffer, add_mul, Ctmp, A[i, k], B[k, j])
-            end
-            C[i, j] = Ctmp
+function buffered_operate!(
+    buffer,
+    ::typeof(add_mul),
+    C::Vector,
+    A::AbstractMatrix,
+    B::AbstractVector,
+)
+    _dim_check(C, A, B)
+    for (ci, ai) in zip(axes(C, 1), axes(A, 1))
+        for (aj, bj) in zip(axes(A, 2), axes(B, 1))
+            C[ci] = buffered_operate!!(buffer, add_mul, C[ci], A[ai, aj], B[bj])
         end
-    end # @inbounds
+    end
     return C
 end
 
 function buffered_operate!(
     buffer,
     ::typeof(add_mul),
-    C::VecOrMat,
+    C::Matrix,
     A::AbstractMatrix,
-    B::AbstractVecOrMat,
+    B::AbstractMatrix,
 )
     _dim_check(C, A, B)
-    return _add_mul_array(buffer, C, A, B)
+    for (ci, ai) in zip(axes(C, 1), axes(A, 1))
+        for (cj, bj) in zip(axes(C, 2), axes(B, 2))
+            for (aj, bi) in zip(axes(A, 2), axes(B, 1))
+                C[ci, cj] = buffered_operate!!(
+                    buffer,
+                    add_mul,
+                    C[ci, cj],
+                    A[ai, aj],
+                    B[bi, bj],
+                )
+            end
+        end
+    end
+    return C
 end
 
 function buffer_for(