diff --git a/src/interpreter/forward_mode.jl b/src/interpreter/forward_mode.jl
index 66598f27b3..eaee2710cc 100644
--- a/src/interpreter/forward_mode.jl
+++ b/src/interpreter/forward_mode.jl
@@ -46,7 +46,7 @@ function build_frule(
         else
             # Derive forward-pass IR, and shove in a `MistyClosure`.
             dual_ir, captures, info = generate_dual_ir(interp, sig_or_mi; debug_mode)
-            dual_oc = optimized_misty_closure(
+            dual_oc = misty_closure(
                 info.dual_ret_type, dual_ir, captures...; do_compile=true
             )
             raw_rule = DerivedFRule{sig,typeof(dual_oc),info.isva,info.nargs}(dual_oc)
@@ -109,6 +109,9 @@ function generate_dual_ir(
 
     # Grab code associated to the primal.
     primal_ir, _ = lookup_ir(interp, sig_or_mi)
+    @static if VERSION > v"1.12-"
+        primal_ir = set_valid_world!(primal_ir, interp.world)
+    end
     nargs = length(primal_ir.argtypes)
 
     # Normalise the IR.
diff --git a/src/interpreter/ir_utils.jl b/src/interpreter/ir_utils.jl
index 043347a353..8423336a82 100644
--- a/src/interpreter/ir_utils.jl
+++ b/src/interpreter/ir_utils.jl
@@ -136,7 +136,7 @@ function __infer_ir!(ir, interp::CC.AbstractInterpreter, mi::CC.MethodInstance)
         propagate_inbounds = true
         spec_info = CC.SpecInfo(nargs, isva, propagate_inbounds, nothing)
         min_world = world = get_inference_world(interp)
-        max_world = Base.get_world_counter()
+        max_world = Base.get_world_counter() # TODO: why do we allow other worlds?
         irsv = CC.IRInterpretationState(
             interp, spec_info, ir, mi, ir.argtypes, world, min_world, max_world
         )
@@ -285,6 +285,37 @@ function lookup_ir(::CC.AbstractInterpreter, mc::MistyClosure; optimize_until=no
     return mc.ir[], return_type(mc.oc)
 end
 
+@static if VERSION > v"1.12-"
+    """
+        set_valid_world!(ir::IRCode, world::UInt)::IRCode
+
+    (1.12+ only)
+    Create a shallow copy of the given IR code, with its `valid_worlds` field updated
+    to a single valid world. This allows the compiler to perform more inlining.
+
+    In particular, if the IR comes from say a function `f` which makes a call to another
+    function `g` which only got defined after `f`, then at the min_world when `f` was
+    defined, `g` was not available yet. If we restrict the IR to a world where `g` is
+    available then `g` can be inlined.
+
+    Will error if `world` is not in the existing `valid_worlds` of `ir`.
+    """
+    function set_valid_world!(ir::IRCode, world::UInt)
+        if world ∉ ir.valid_worlds
+            error("World $world is not valid for this IRCode: $(ir.valid_worlds).")
+        end
+        return CC.IRCode(
+            ir.stmts,
+            ir.cfg,
+            ir.debuginfo,
+            ir.argtypes,
+            ir.meta,
+            ir.sptypes,
+            CC.WorldRange(world, world),
+        )
+    end
+end
+
 return_type(::Core.OpaqueClosure{A,B}) where {A,B} = B
 
 """
diff --git a/src/interpreter/reverse_mode.jl b/src/interpreter/reverse_mode.jl
index b80be6f3e1..e9b50aca4f 100644
--- a/src/interpreter/reverse_mode.jl
+++ b/src/interpreter/reverse_mode.jl
@@ -1134,10 +1134,10 @@ function build_rrule(
         else
             # Derive forwards- and reverse-pass IR, and shove in `MistyClosure`s.
             dri = generate_ir(interp, sig_or_mi; debug_mode)
-            fwd_oc = optimized_misty_closure(
+            fwd_oc = misty_closure(
                 dri.fwd_ret_type, dri.fwd_ir, dri.shared_data...
             )
-            rvs_oc = optimized_misty_closure(
+            rvs_oc = misty_closure(
                 dri.rvs_ret_type, dri.rvs_ir, dri.shared_data...
             )
 
@@ -1181,6 +1181,9 @@ function generate_ir(
 
     # Grab code associated to the primal.
     ir, _ = lookup_ir(interp, sig_or_mi)
+    @static if VERSION > v"1.12-"
+        ir = set_valid_world!(ir, interp.world)
+    end
     Treturn = compute_ir_rettype(ir)
     fwd_ret_type = forwards_ret_type(ir)
     rvs_ret_type = pullback_ret_type(ir)
diff --git a/src/utils.jl b/src/utils.jl
index b5c01fe61e..5745b3b4cc 100644
--- a/src/utils.jl
+++ b/src/utils.jl
@@ -354,55 +354,6 @@ function opaque_closure(
     )::Core.OpaqueClosure{sig,ret_type}
 end
 
-function optimized_opaque_closure(rtype, ir::IRCode, env...; kwargs...)
-    oc = opaque_closure(rtype, ir, env...; kwargs...)
-    world = UInt(oc.world)
-    set_world_bounds_for_optimization!(oc)
-    optimized_oc = optimize_opaque_closure(oc, rtype, env...; kwargs...)
-    return optimized_oc
-end
-
-function optimize_opaque_closure(oc::Core.OpaqueClosure, rtype, env...; kwargs...)
-    method = oc.source
-    ci = method.specializations.cache
-    world = UInt(oc.world)
-    ir = reinfer_and_inline(ci, world)
-    ir === nothing && return oc # nothing to optimize
-    return opaque_closure(rtype, ir, env...; kwargs...)
-end
-
-# Allows optimization to make assumptions about binding access,
-# enabling inlining and other optimizations.
-function set_world_bounds_for_optimization!(oc::Core.OpaqueClosure)
-    ci = oc.source.specializations.cache
-    ci.inferred === nothing && return nothing
-    ci.inferred.min_world = oc.world
-    ci.inferred.max_world = oc.world
-end
-
-function reinfer_and_inline(ci::Core.CodeInstance, world::UInt)
-    interp = CC.NativeInterpreter(world)
-    mi = get_mi(ci)
-    argtypes = collect(Any, mi.specTypes.parameters)
-    irsv = CC.IRInterpretationState(interp, ci, mi, argtypes, world)
-    irsv === nothing && return nothing
-    for stmt in irsv.ir.stmts
-        inst = stmt[:inst]
-        if isexpr(inst, :loopinfo) ||
-            isexpr(inst, :pop_exception) ||
-            isa(inst, CC.GotoIfNot) ||
-            isa(inst, CC.GotoNode) ||
-            isexpr(inst, :copyast)
-            continue
-        end
-        stmt[:flag] |= CC.IR_FLAG_REFINED
-    end
-    CC.ir_abstract_constant_propagation(interp, irsv)
-    state = CC.InliningState(interp)
-    ir = CC.ssa_inlining_pass!(irsv.ir, state, CC.propagate_inbounds(irsv))
-    return ir
-end
-
 """
     misty_closure(
         ret_type::Type,
@@ -425,18 +376,6 @@ function misty_closure(
     return MistyClosure(opaque_closure(ret_type, ir, env...; isva, do_compile), Ref(ir))
 end
 
-function optimized_misty_closure(
-    ret_type::Type,
-    ir::IRCode,
-    @nospecialize env...;
-    isva::Bool=false,
-    do_compile::Bool=true,
-)
-    return MistyClosure(
-        optimized_opaque_closure(ret_type, ir, env...; isva, do_compile), Ref(ir)
-    )
-end
-
 @static if VERSION > v"1.12-"
     compute_ir_rettype(ir) = CC.compute_ir_rettype(ir)
     compute_oc_signature(ir, nargs, isva) = CC.compute_oc_signature(ir, nargs, isva)
diff --git a/test/interpreter/ir_utils.jl b/test/interpreter/ir_utils.jl
index e4d91472f0..1e7b5f64ed 100644
--- a/test/interpreter/ir_utils.jl
+++ b/test/interpreter/ir_utils.jl
@@ -20,8 +20,6 @@ end
         @test length(stmt(ir.stmts)) == length(src.code)
         oc = Mooncake.opaque_closure(rettype, ir)
         @test oc(args...) == f(args...)
-        oc = Mooncake.optimized_opaque_closure(rettype, ir)
-        @test oc(args...) == f(args...)
     end
     @testset "infer_ir!" begin
 
@@ -44,8 +42,6 @@ end
         ir.argtypes[1] = Tuple
         oc = Mooncake.opaque_closure(Float64, ir)
         @test oc(5.0) == cos(sin(5.0))
-        oc = Mooncake.optimized_opaque_closure(Float64, ir)
-        @test oc(5.0) == cos(sin(5.0))
     end
     @testset "lookup_ir" begin
         tt = Tuple{typeof(sin),Float64}
diff --git a/test/utils.jl b/test/utils.jl
index 09ee3d251f..6d075e2488 100644
--- a/test/utils.jl
+++ b/test/utils.jl
@@ -116,14 +116,9 @@
         oc2 = Mooncake.opaque_closure(Any, ir)
         @test oc2 isa Core.OpaqueClosure{Tuple{Float64},Any}
         @test oc2(5.0) == sin(5.0)
-        oc2 = Mooncake.optimized_opaque_closure(Any, ir)
-        @test oc2 isa Core.OpaqueClosure{Tuple{Float64},Any}
-        @test oc2(5.0) == sin(5.0)
 
         # Check that we can get a MistyClosure also.
         mc = Mooncake.misty_closure(Float64, ir)
         @test mc(5.0) == sin(5.0)
-        mc = Mooncake.optimized_misty_closure(Float64, ir)
-        @test mc(5.0) == sin(5.0)
     end
 end