Fail when simd=:ivdep is used with foldl etc.

src/processes.jl

@@ -363,6 +363,7 @@ end
 function Base.mapfoldl(xform::Transducer, step, itr;
                        simd::SIMDFlag = Val(false),
                        init = MissingInit())
+    check_no_ivdep(simd)
     unreduced(transduce(xform, step, init, itr; simd=simd))
 end
 
@@ -724,17 +725,20 @@ julia> foldl(Filter(isodd), 1:4, init=0.0) do state, input
 """
 function Base.foldl(step, xform::Transducer, itr;
                     kw...)
+    check_no_ivdep(; kw...)
     mapfoldl(xform, Completing(step), itr; kw...)
 end
 
-@inline Base.foldl(step, ed::Eduction; init=MissingInit(), kwargs...) =
+@inline function Base.foldl(step, ed::Eduction; init=MissingInit(), kwargs...)
+    check_no_ivdep(; kwargs...)
     if FinalType(ed.rf) === NOTYPE
         xf = Transducer(ed.rf)
         unreduced(transduce(xf, Completing(step), init, ed.coll; kwargs...))
     else
         rf = reform(ed.rf, Completing(step))
         unreduced(transduce(rf, init, ed.coll; kwargs...))
     end
+end
 
 """
     foreach(eff, xf::Transducer, reducible; simd)

src/simd.jl

@@ -98,6 +98,20 @@ end
 
 const SIMDFlag = Union{Bool, Symbol, Val{true}, Val{false}, Val{:ivdep}}
 
+"""
+    check_no_ivdep(::SIMDFlag)
+    check_no_ivdep(; simd=Val(false), kwargs...)
+"""
+@inline check_no_ivdep(simd) = simd
+@inline check_no_ivdep(simd::Symbol) =
+    simd == :ivdep ? check_no_ivdep(Val(:ivdep)) : simd
+@noinline check_no_ivdep(::Val{:ivdep}) =
+    throw(ArgumentError(string(
+        "`simd=:ivdep` must not be used for generic `foldl` or `reduce`.",
+        " Please use `foreach`."
+    )))
+check_no_ivdep(; simd=Val(false), _...) = check_no_ivdep(simd)
+
 """
     maybe_usesimd(xform, simd)
 

test/test_simd.jl

@@ -51,6 +51,17 @@ end
     end
 end
 
+@testset "UX" begin
+    for err in [
+        (@test_error mapfoldl(Map(identity), +, 1:2; simd=:ivdep)),
+        (@test_error foldl(+, Map(identity), 1:2; simd=:ivdep)),
+        (@test_error foldl(+, eduction(Map(identity), 1:2); simd=:ivdep)),
+    ]
+        @test occursin("`simd=:ivdep` must not be used",
+                       sprint(showerror, err))
+    end
+end
+
 @testset "@simd_if" begin
     err = @test_error @macroexpand @simd_if rf for i in 1:1
     end