diff --git a/base/compiler/abstractinterpretation.jl b/base/compiler/abstractinterpretation.jl
index 22bc1cf046d98..a7602f8cd4134 100644
--- a/base/compiler/abstractinterpretation.jl
+++ b/base/compiler/abstractinterpretation.jl
@@ -13,6 +13,31 @@ call_result_unused(sv::InferenceState, currpc::Int) =
     isexpr(sv.src.code[currpc], :call) && isempty(sv.ssavalue_uses[currpc])
 call_result_unused(si::StmtInfo) = !si.used
 
+is_const_bool_or_bottom(@nospecialize(b)) = (isa(b, Const) && isa(b.val, Bool)) || b == Bottom
+function can_propagate_conditional(@nospecialize(rt), argtypes::Vector{Any})
+    isa(rt, InterConditional) || return false
+    if rt.slot > length(argtypes)
+        # In the vararg tail - can't be conditional
+        @assert isvarargtype(argtypes[end])
+        return false
+    end
+    return isa(argtypes[rt.slot], Conditional) &&
+        is_const_bool_or_bottom(rt.thentype) && is_const_bool_or_bottom(rt.thentype)
+end
+
+function propagate_conditional(rt::InterConditional, cond::Conditional)
+    new_thentype = rt.thentype === Const(false) ? cond.elsetype : cond.thentype
+    new_elsetype = rt.elsetype === Const(true) ? cond.thentype : cond.elsetype
+    if rt.thentype == Bottom
+        @assert rt.elsetype != Bottom
+        return Conditional(cond.slot, Bottom, new_elsetype)
+    elseif rt.elsetype == Bottom
+        @assert rt.thentype != Bottom
+        return Conditional(cond.slot, new_thentype, Bottom)
+    end
+    return Conditional(cond.slot, new_thentype, new_elsetype)
+end
+
 function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
                                   arginfo::ArgInfo, si::StmtInfo, @nospecialize(atype),
                                   sv::AbsIntState, max_methods::Int)
@@ -156,6 +181,15 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
         end
         @assert !(this_conditional isa Conditional || this_rt isa MustAlias) "invalid lattice element returned from inter-procedural context"
         seen += 1
+
+        if can_propagate_conditional(this_conditional, argtypes)
+            # The only case where we need to keep this in rt is where
+            # we can directly propagate the conditional to a slot argument
+            # that is not one of our arguments, otherwise we keep all the
+            # relevant information in `conditionals` below.
+            this_rt = this_conditional
+        end
+
         rettype = rettype ⊔ₚ this_rt
         exctype = exctype ⊔ₚ this_exct
         if has_conditional(𝕃ₚ, sv) && this_conditional !== Bottom && is_lattice_bool(𝕃ₚ, rettype) && fargs !== nothing
@@ -409,6 +443,9 @@ function from_interconditional(𝕃ᵢ::AbstractLattice, @nospecialize(rt), sv::
     has_conditional(𝕃ᵢ, sv) || return widenconditional(rt)
     (; fargs, argtypes) = arginfo
     fargs === nothing && return widenconditional(rt)
+    if can_propagate_conditional(rt, argtypes)
+        return propagate_conditional(rt, argtypes[rt.slot]::Conditional)
+    end
     slot = 0
     alias = nothing
     thentype = elsetype = Any
@@ -2217,13 +2254,6 @@ function abstract_call_known(interp::AbstractInterpreter, @nospecialize(f),
         end
     elseif is_return_type(f)
         return return_type_tfunc(interp, argtypes, si, sv)
-    elseif la == 2 && istopfunction(f, :!)
-        # handle Conditional propagation through !Bool
-        aty = argtypes[2]
-        if isa(aty, Conditional)
-            call = abstract_call_gf_by_type(interp, f, ArgInfo(fargs, Any[Const(f), Bool]), si, Tuple{typeof(f), Bool}, sv, max_methods) # make sure we've inferred `!(::Bool)`
-            return CallMeta(Conditional(aty.slot, aty.elsetype, aty.thentype), Any, call.effects, call.info)
-        end
     elseif la == 3 && istopfunction(f, :!==)
         # mark !== as exactly a negated call to ===
         call = abstract_call_gf_by_type(interp, f, ArgInfo(fargs, Any[Const(f), Any, Any]), si, Tuple{typeof(f), Any, Any}, sv, max_methods)
@@ -3194,7 +3224,7 @@ function update_bestguess!(interp::AbstractInterpreter, frame::InferenceState,
     # narrow representation of bestguess slightly to prepare for tmerge with rt
     if rt isa InterConditional && bestguess isa Const
         slot_id = rt.slot
-        old_id_type = slottypes[slot_id]
+        old_id_type = widenconditional(slottypes[slot_id])
         if bestguess.val === true && rt.elsetype !== Bottom
             bestguess = InterConditional(slot_id, old_id_type, Bottom)
         elseif bestguess.val === false && rt.thentype !== Bottom
diff --git a/base/compiler/inferencestate.jl b/base/compiler/inferencestate.jl
index c358b1177251f..38011656e41ea 100644
--- a/base/compiler/inferencestate.jl
+++ b/base/compiler/inferencestate.jl
@@ -312,6 +312,9 @@ mutable struct InferenceState
         nargtypes = length(argtypes)
         for i = 1:nslots
             argtyp = (i > nargtypes) ? Bottom : argtypes[i]
+            if argtyp === Bool && has_conditional(typeinf_lattice(interp))
+                argtyp = Conditional(i, Const(true), Const(false))
+            end
             slottypes[i] = argtyp
             bb_vartable1[i] = VarState(argtyp, i > nargtypes)
         end
diff --git a/base/compiler/tfuncs.jl b/base/compiler/tfuncs.jl
index 28e883d83312c..b40f65ab3ca1d 100644
--- a/base/compiler/tfuncs.jl
+++ b/base/compiler/tfuncs.jl
@@ -227,10 +227,19 @@ end
 @nospecs shift_tfunc(𝕃::AbstractLattice, x, y) = shift_tfunc(widenlattice(𝕃), x, y)
 @nospecs shift_tfunc(::JLTypeLattice, x, y) = widenconst(x)
 
+function not_tfunc(𝕃::AbstractLattice, @nospecialize(b))
+    if isa(b, Conditional)
+        return Conditional(b.slot, b.elsetype, b.thentype)
+    elseif isa(b, Const)
+        return Const(not_int(b.val))
+    end
+    return math_tfunc(𝕃, b)
+end
+
 add_tfunc(and_int, 2, 2, and_int_tfunc, 1)
 add_tfunc(or_int, 2, 2, or_int_tfunc, 1)
 add_tfunc(xor_int, 2, 2, math_tfunc, 1)
-add_tfunc(not_int, 1, 1, math_tfunc, 0) # usually used as not_int(::Bool) to negate a condition
+add_tfunc(not_int, 1, 1, not_tfunc, 0) # usually used as not_int(::Bool) to negate a condition
 add_tfunc(shl_int, 2, 2, shift_tfunc, 1)
 add_tfunc(lshr_int, 2, 2, shift_tfunc, 1)
 add_tfunc(ashr_int, 2, 2, shift_tfunc, 1)
diff --git a/test/compiler/inference.jl b/test/compiler/inference.jl
index 8b6da828af54d..9ae98b884bef4 100644
--- a/test/compiler/inference.jl
+++ b/test/compiler/inference.jl
@@ -5866,3 +5866,8 @@ end
 bar54341(args...) = foo54341(4, args...)
 
 @test Core.Compiler.return_type(bar54341, Tuple{Vararg{Int}}) === Int
+
+# InterConditional rt with Vararg argtypes
+fcondvarargs(a, b, c, d) = isa(d, Int64)
+gcondvarargs(a, x...) = return fcondvarargs(a, x...) ? isa(a, Int64) : !isa(a, Int64)
+@test Core.Compiler.return_type(gcondvarargs, Tuple{Vararg{Any}}) === Bool