The `IfLifting` pass doesn't seem to be working quite right

[mtiller-jh]

Describe the bug 🐞

If I add additional_passes=[IfLifting] to an @mtkbuild call, I get an error.

Expected behavior

I would not expect to get an error message.

Minimal Reproducible Example 👇

Clone https://github.com/JuliaComputing/BlockComponents and checkout the mmt/if-lifting branch. Attempt to run ]test and you'll get:

Error & Stacktrace ⚠️

  Got exception outside of a @test
  MethodError: no method matching iterate(::Expr)
  The function `iterate` exists, but no method is defined for this combination of argument types.
  
  Closest candidates are:
    iterate(::Expronicon.JLIfElse)
     @ Expronicon ~/.julia/packages/Expronicon/Oa1rJ/src/types.jl:427
    iterate(::Expronicon.JLIfElse, ::Any)
     @ Expronicon ~/.julia/packages/Expronicon/Oa1rJ/src/types.jl:427
    iterate(::Combinatorics.Combinations)
     @ Combinatorics ~/.julia/packages/Combinatorics/Udg6X/src/combinations.jl:13
    ...
  
  Stacktrace:
    [1] structural_simplify(sys::ODESystem, io::Nothing; additional_passes::Expr, simplify::Bool, split::Bool, allow_symbolic::Bool, allow_parameter::Bool, conservative::Bool, fully_determined::Bool, kwargs::@Kwargs{})
      @ ModelingToolkit ~/.julia/packages/ModelingToolkit/41wGH/src/systems/systems.jl:49
    [2] macro expansion
      @ ~/.julia/packages/ModelingToolkit/41wGH/src/systems/abstractsystem.jl:2279 [inlined]
    [3] macro expansion
      @ ~/Source/jsml/jsml-kernel/test-libraries/BlockComponents/generated/Add3Test_test.jl:10 [inlined]
    [4] macro expansion
      @ ~/.julia/juliaup/julia-1.11.3+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/Test/src/Test.jl:1704 [inlined]
    [5] top-level scope
      @ ~/Source/jsml/jsml-kernel/test-libraries/BlockComponents/generated/Add3Test_test.jl:8
    [6] include(fname::String)
      @ Main ./sysimg.jl:38
    [7] top-level scope
      @ ~/Source/jsml/jsml-kernel/test-libraries/BlockComponents/generated/tests.jl:16
    [8] include(fname::String)
      @ Main ./sysimg.jl:38
    [9] top-level scope
      @ ~/Source/jsml/jsml-kernel/test-libraries/BlockComponents/test/runtests.jl:5
   [10] include(fname::String)
      @ Main ./sysimg.jl:38
   [11] top-level scope
      @ none:6
   [12] eval
      @ ./boot.jl:430 [inlined]
   [13] exec_options(opts::Base.JLOptions)
      @ Base ./client.jl:296
   [14] _start()
      @ Base ./client.jl:531

Environment (please complete the following information):

• Output of using Pkg; Pkg.status()

Project BlockComponents v0.12.4
Status `~/Source/jsml/jsml-kernel/test-libraries/BlockComponents/Project.toml`
  [3626b584] JuliaSimCore v0.3.0
⌅ [961ee093] ModelingToolkit v9.61.0
  [50262376] OrdinaryDiffEqDefault v1.2.0
  [aea7be01] PrecompileTools v1.2.1
  [7e49a35a] RuntimeGeneratedFunctions v0.5.13
Info Packages marked with ⌅ have new versions available but compatibility constraints restrict them from upgrading. To see why use `status --outdated`

• Output of using Pkg; Pkg.status(; mode = PKGMODE_MANIFEST)

(BlockComponents) pkg> status --manifest
Project BlockComponents v0.12.4
Status `~/Source/jsml/jsml-kernel/test-libraries/BlockComponents/Manifest.toml`
⌃ [47edcb42] ADTypes v1.12.0
  [621f4979] AbstractFFTs v1.5.0
  [1520ce14] AbstractTrees v0.4.5
  [7d9f7c33] Accessors v0.1.41
  [79e6a3ab] Adapt v4.1.1
  [66dad0bd] AliasTables v1.1.3
  [ec485272] ArnoldiMethod v0.4.0
  [4fba245c] ArrayInterface v7.18.0
  [4c555306] ArrayLayouts v1.11.0
⌃ [a9b6321e] Atomix v1.0.1
  [e2ed5e7c] Bijections v0.1.9
  [62783981] BitTwiddlingConvenienceFunctions v0.1.6
  [8e7c35d0] BlockArrays v1.3.0
  [70df07ce] BracketingNonlinearSolve v1.1.0
  [fa961155] CEnum v0.5.0
  [2a0fbf3d] CPUSummary v0.2.6
  [00ebfdb7] CSTParser v3.4.3
  [7057c7e9] Cassette v0.3.14
  [082447d4] ChainRules v1.72.2
  [d360d2e6] ChainRulesCore v1.25.1
  [fb6a15b2] CloseOpenIntervals v0.1.13
  [861a8166] Combinatorics v1.0.2
  [a80b9123] CommonMark v0.8.15
  [38540f10] CommonSolve v0.2.4
  [bbf7d656] CommonSubexpressions v0.3.1
  [f70d9fcc] CommonWorldInvalidations v1.0.0
  [34da2185] Compat v4.16.0
  [b152e2b5] CompositeTypes v0.1.4
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  [2569d6c7] ConcreteStructs v0.2.3
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  [a93c6f00] DataFrames v1.7.0
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  [459566f4] DiffEqCallbacks v4.2.2
  [77a26b50] DiffEqNoiseProcess v5.24.1
  [163ba53b] DiffResults v1.1.0
  [b552c78f] DiffRules v1.15.1
⌃ [a0c0ee7d] DifferentiationInterface v0.6.31
  [31c24e10] Distributions v0.25.117
  [ffbed154] DocStringExtensions v0.9.3
  [5b8099bc] DomainSets v0.7.15
  [7c1d4256] DynamicPolynomials v0.6.1
⌃ [06fc5a27] DynamicQuantities v0.13.2
  [4e289a0a] EnumX v1.0.4
⌃ [7da242da] Enzyme v0.13.28
  [f151be2c] EnzymeCore v0.8.8
  [e2ba6199] ExprTools v0.1.10
⌅ [6b7a57c9] Expronicon v0.8.5
  [7034ab61] FastBroadcast v0.3.5
  [9aa1b823] FastClosures v0.3.2
  [29a986be] FastLapackInterface v2.0.4
  [a4df4552] FastPower v1.1.1
  [1a297f60] FillArrays v1.13.0
  [64ca27bc] FindFirstFunctions v1.4.1
⌃ [6a86dc24] FiniteDiff v2.26.2
  [1fa38f19] Format v1.3.7
  [f6369f11] ForwardDiff v0.10.38
  [f62d2435] FunctionProperties v0.1.2
  [069b7b12] FunctionWrappers v1.1.3
  [77dc65aa] FunctionWrappersWrappers v0.1.3
  [d9f16b24] Functors v0.5.2
  [0c68f7d7] GPUArrays v11.2.1
  [46192b85] GPUArraysCore v0.2.0
  [61eb1bfa] GPUCompiler v1.1.0
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  [86223c79] Graphs v1.12.0
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  [3e5b6fbb] HostCPUFeatures v0.1.17
  [34004b35] HypergeometricFunctions v0.3.27
  [7869d1d1] IRTools v0.4.14
  [615f187c] IfElse v0.1.1
  [d25df0c9] Inflate v0.1.5
  [842dd82b] InlineStrings v1.4.2
  [18e54dd8] IntegerMathUtils v0.1.2
  [8197267c] IntervalSets v0.7.10
  [3587e190] InverseFunctions v0.1.17
  [41ab1584] InvertedIndices v1.3.1
⌃ [92d709cd] IrrationalConstants v0.2.2
  [82899510] IteratorInterfaceExtensions v1.0.0
  [692b3bcd] JLLWrappers v1.7.0
  [682c06a0] JSON v0.21.4
  [0f8b85d8] JSON3 v1.14.1
  [7d188eb4] JSONSchema v1.4.1
  [98e50ef6] JuliaFormatter v1.0.62
  [9c9cc66b] JuliaSimBase v2.1.1
  [3626b584] JuliaSimCore v0.3.0
  [ccbc3e58] JumpProcesses v9.14.1
  [ef3ab10e] KLU v0.6.0
⌃ [63c18a36] KernelAbstractions v0.9.31
  [ba0b0d4f] Krylov v0.9.9
  [5be7bae1] LBFGSB v0.4.1
  [929cbde3] LLVM v9.2.0
  [b964fa9f] LaTeXStrings v1.4.0
  [23fbe1c1] Latexify v0.16.5
  [10f19ff3] LayoutPointers v0.1.17
⌃ [5078a376] LazyArrays v2.3.2
  [1d6d02ad] LeftChildRightSiblingTrees v0.2.0
  [87fe0de2] LineSearch v0.1.4
  [d3d80556] LineSearches v7.3.0
  [7ed4a6bd] LinearSolve v2.38.0
  [2ab3a3ac] LogExpFunctions v0.3.29
  [e6f89c97] LoggingExtras v1.1.0
  [bdcacae8] LoopVectorization v0.12.171
  [d8e11817] MLStyle v0.4.17
  [1914dd2f] MacroTools v0.5.15
  [d125e4d3] ManualMemory v0.1.8
  [bb5d69b7] MaybeInplace v0.1.4
  [e1d29d7a] Missings v1.2.0
⌅ [961ee093] ModelingToolkit v9.61.0
  [46d2c3a1] MuladdMacro v0.2.4
  [102ac46a] MultivariatePolynomials v0.5.7
⌃ [d8a4904e] MutableArithmetics v1.6.2
  [d41bc354] NLSolversBase v7.8.3
  [872c559c] NNlib v0.9.27
⌃ [77ba4419] NaNMath v1.1.1
  [8913a72c] NonlinearSolve v4.3.0
  [be0214bd] NonlinearSolveBase v1.4.0
  [5959db7a] NonlinearSolveFirstOrder v1.2.0
  [9a2c21bd] NonlinearSolveQuasiNewton v1.1.0
  [26075421] NonlinearSolveSpectralMethods v1.1.0
  [d8793406] ObjectFile v0.4.3
  [6fe1bfb0] OffsetArrays v1.15.0
  [429524aa] Optim v1.11.0
  [3bd65402] Optimisers v0.4.4
  [7f7a1694] Optimization v4.1.0
  [bca83a33] OptimizationBase v2.4.0
⌃ [bac558e1] OrderedCollections v1.7.0
  [6ad6398a] OrdinaryDiffEqBDF v1.2.0
⌅ [bbf590c4] OrdinaryDiffEqCore v1.15.0
  [50262376] OrdinaryDiffEqDefault v1.2.0
  [4302a76b] OrdinaryDiffEqDifferentiation v1.3.0
  [127b3ac7] OrdinaryDiffEqNonlinearSolve v1.3.0
  [43230ef6] OrdinaryDiffEqRosenbrock v1.4.0
  [2d112036] OrdinaryDiffEqSDIRK v1.2.0
  [b1df2697] OrdinaryDiffEqTsit5 v1.1.0
  [79d7bb75] OrdinaryDiffEqVerner v1.1.1
  [90014a1f] PDMats v0.11.32
  [65ce6f38] PackageExtensionCompat v1.0.2
  [d96e819e] Parameters v0.12.3
  [69de0a69] Parsers v2.8.1
  [e409e4f3] PoissonRandom v0.4.4
  [f517fe37] Polyester v0.7.16
  [1d0040c9] PolyesterWeave v0.2.2
  [2dfb63ee] PooledArrays v1.4.3
  [85a6dd25] PositiveFactorizations v0.2.4
  [d236fae5] PreallocationTools v0.4.24
  [aea7be01] PrecompileTools v1.2.1
  [21216c6a] Preferences v1.4.3
  [08abe8d2] PrettyTables v2.4.0
  [27ebfcd6] Primes v0.5.6
  [33c8b6b6] ProgressLogging v0.1.4
  [92933f4c] ProgressMeter v1.10.2
  [43287f4e] PtrArrays v1.3.0
  [1fd47b50] QuadGK v2.11.1
  [74087812] Random123 v1.7.0
  [e6cf234a] RandomNumbers v1.6.0
  [c1ae055f] RealDot v0.1.0
  [3cdcf5f2] RecipesBase v1.3.4
⌃ [731186ca] RecursiveArrayTools v3.27.4
  [f2c3362d] RecursiveFactorization v0.2.23
  [189a3867] Reexport v1.2.2
  [05181044] RelocatableFolders v1.0.1
  [ae029012] Requires v1.3.0
  [ae5879a3] ResettableStacks v1.1.1
  [37e2e3b7] ReverseDiff v1.15.3
  [79098fc4] Rmath v0.8.0
  [7e49a35a] RuntimeGeneratedFunctions v0.5.13
  [9dfe8606] SCCNonlinearSolve v1.0.0
  [94e857df] SIMDTypes v0.1.0
  [476501e8] SLEEFPirates v0.6.43
⌃ [0bca4576] SciMLBase v2.72.0
  [19f34311] SciMLJacobianOperators v0.1.1
  [c0aeaf25] SciMLOperators v0.3.12
  [1ed8b502] SciMLSensitivity v7.72.0
  [53ae85a6] SciMLStructures v1.6.1
  [7e506255] ScopedValues v1.3.0
  [6c6a2e73] Scratch v1.2.1
  [91c51154] SentinelArrays v1.4.8
  [efcf1570] Setfield v1.1.1
  [727e6d20] SimpleNonlinearSolve v2.1.0
  [699a6c99] SimpleTraits v0.9.4
  [ce78b400] SimpleUnPack v1.1.0
  [a2af1166] SortingAlgorithms v1.2.1
⌃ [9f842d2f] SparseConnectivityTracer v0.6.9
  [47a9eef4] SparseDiffTools v2.23.1
  [dc90abb0] SparseInverseSubset v0.1.2
⌃ [0a514795] SparseMatrixColorings v0.4.11
  [e56a9233] Sparspak v0.3.9
  [276daf66] SpecialFunctions v2.5.0
  [aedffcd0] Static v1.1.1
  [0d7ed370] StaticArrayInterface v1.8.0
⌃ [90137ffa] StaticArrays v1.9.10
  [1e83bf80] StaticArraysCore v1.4.3
  [10745b16] Statistics v1.11.1
  [82ae8749] StatsAPI v1.7.0
  [2913bbd2] StatsBase v0.34.4
  [4c63d2b9] StatsFuns v1.3.2
  [7792a7ef] StrideArraysCore v0.5.7
  [892a3eda] StringManipulation v0.4.0
⌃ [09ab397b] StructArrays v0.6.21
  [53d494c1] StructIO v0.3.1
  [856f2bd8] StructTypes v1.11.0
  [2efcf032] SymbolicIndexingInterface v0.3.37
  [19f23fe9] SymbolicLimits v0.2.2
⌅ [d1185830] SymbolicUtils v3.11.0
⌅ [0c5d862f] Symbolics v6.24.0
  [3783bdb8] TableTraits v1.0.1
  [bd369af6] Tables v1.12.0
  [8ea1fca8] TermInterface v2.0.0
  [5d786b92] TerminalLoggers v0.1.7
  [8290d209] ThreadingUtilities v0.5.2
  [a759f4b9] TimerOutputs v0.5.26
  [0796e94c] Tokenize v0.5.29
  [9f7883ad] Tracker v0.2.37
  [d5829a12] TriangularSolve v0.2.1
  [410a4b4d] Tricks v0.1.10
  [781d530d] TruncatedStacktraces v1.4.0
  [5c2747f8] URIs v1.5.1
  [3a884ed6] UnPack v1.0.2
  [1986cc42] Unitful v1.22.0
  [a7c27f48] Unityper v0.1.6
  [013be700] UnsafeAtomics v0.3.0
  [3d5dd08c] VectorizationBase v0.21.71
  [19fa3120] VertexSafeGraphs v0.2.0
  [897b6980] WeakValueDicts v0.1.0
⌅ [e88e6eb3] Zygote v0.6.75
  [700de1a5] ZygoteRules v0.2.7
  [7cc45869] Enzyme_jll v0.0.172+0
  [1d5cc7b8] IntelOpenMP_jll v2025.0.4+0
  [dad2f222] LLVMExtra_jll v0.0.35+0
  [81d17ec3] L_BFGS_B_jll v3.0.1+0
  [856f044c] MKL_jll v2025.0.1+1
  [efe28fd5] OpenSpecFun_jll v0.5.6+0
  [f50d1b31] Rmath_jll v0.5.1+0
  [1317d2d5] oneTBB_jll v2021.12.0+0
  [0dad84c5] ArgTools v1.1.2
  [56f22d72] Artifacts v1.11.0
  [2a0f44e3] Base64 v1.11.0
  [ade2ca70] Dates v1.11.0
  [8ba89e20] Distributed v1.11.0
  [f43a241f] Downloads v1.6.0
  [7b1f6079] FileWatching v1.11.0
  [9fa8497b] Future v1.11.0
  [b77e0a4c] InteractiveUtils v1.11.0
  [4af54fe1] LazyArtifacts v1.11.0
  [b27032c2] LibCURL v0.6.4
  [76f85450] LibGit2 v1.11.0
  [8f399da3] Libdl v1.11.0
  [37e2e46d] LinearAlgebra v1.11.0
  [56ddb016] Logging v1.11.0
  [d6f4376e] Markdown v1.11.0
  [a63ad114] Mmap v1.11.0
  [ca575930] NetworkOptions v1.2.0
  [44cfe95a] Pkg v1.11.0
  [de0858da] Printf v1.11.0
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  [9e88b42a] Serialization v1.11.0
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  [6462fe0b] Sockets v1.11.0
  [2f01184e] SparseArrays v1.11.0
  [4607b0f0] SuiteSparse
  [fa267f1f] TOML v1.0.3
  [a4e569a6] Tar v1.10.0
  [8dfed614] Test v1.11.0
  [cf7118a7] UUIDs v1.11.0
  [4ec0a83e] Unicode v1.11.0
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  [4536629a] OpenBLAS_jll v0.3.27+1
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Info Packages marked with ⌃ and ⌅ have new versions available. Those with ⌃ may be upgradable, but those with ⌅ are restricted by compatibility constraints from upgrading. To see why use `status --outdated -m`

• Output of versioninfo()

julia> versioninfo()
Julia Version 1.11.3
Commit d63adeda50d (2025-01-21 19:42 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: macOS (arm64-apple-darwin24.0.0)
  CPU: 12 × Apple M2 Max
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, apple-m2)
Threads: 1 default, 0 interactive, 1 GC (on 8 virtual cores)
Environment:
  JULIA_PKG_USE_CLI_GIT = true
  JULIA_PKG_SERVER = internal.juliahub.com

[mtiller-jh]

I want to reopen this because IfLifting is not working for me. Yes, the issue with @mtkbuild may be addressed in newer versions of MTK. But after digging into this I have another MWE that shows that adding IfLifting as an additional pass breaks many models just in a single package.

The MWE is found in the BlockComponents. Simple checkout the mmt/if-lifting-errors branch. If you run ]test, everything will pass. But this is because I removed the IfLifting pass from a bunch of models. If you add it back (just search for # Error with IfLifting in the code. There are eight different models
where the IfLifting pass had to be removed.

I'm pretty confident I'm not doing anything wrong here (all I'm doing is enabling the additional pass).

[BenChung]

@maxesit can you please look at pulling a MWE out of the tests, ideally in MTK?

[maxesit]

This would be the MWE, contains the Cosine, and Integrator components, and a test.

@mtiller-jh is there a way to locally turn off the automatic file generation? I'm unable to change any of the generated .jl files, because as soon as I save them, they get regenerated. Because of this, I wasn't able to check what was the exact error that you had, but this is what I got with the MWE:

Results:

julia> include("mwe_iflifting.jl")
Running test case1 for CosineTest: Test Failed at /home/maxesit/.julia/dev/Internship/MWEs/IfLifting/mwe_iflifting.jl:74
  Expression: ≈((sol[model.integrator.x])[end], 2.45255, atol = 0.001)
   Evaluated: 2.4643039806316422 ≈ 2.45255 (atol=0.001)

Stacktrace:
 [1] macro expansion
   @ ~/.julia/juliaup/julia-1.10.7+0.x64.linux.gnu/share/julia/stdlib/v1.10/Test/src/Test.jl:672 [inlined]
 [2] macro expansion
   @ ~/.julia/dev/Internship/MWEs/IfLifting/mwe_iflifting.jl:74 [inlined]
 [3] macro expansion
   @ ~/.julia/juliaup/julia-1.10.7+0.x64.linux.gnu/share/julia/stdlib/v1.10/Test/src/Test.jl:1577 [inlined]
 [4] top-level scope
   @ ~/.julia/dev/Internship/MWEs/IfLifting/mwe_iflifting.jl:65
Test Summary:                     | Pass  Fail  Total   Time
Running test case1 for CosineTest |    3     1      4  45.9s
ERROR: LoadError: Some tests did not pass: 3 passed, 1 failed, 0 errored, 0 broken.
in expression starting at /home/maxesit/.julia/dev/Internship/MWEs/IfLifting/mwe_iflifting.jl:63

Code:

using ModelingToolkit
using ModelingToolkit: t_nounits as t, D_nounits as D

# Cosine
@component function Cosine(; name, start_time=0, offset=0, amplitude=nothing, frequency=nothing, phase=nothing)
  params = @parameters begin
    (start_time::Float64 = start_time)
    (offset::Float64 = offset)
    (amplitude::Float64 = amplitude)
    (frequency::Float64 = frequency)
    (phase::Float64 = phase)
  end
  vars = @variables begin
    y(t), [output = true]
  end
  eqs = Equation[
    y ~ ifelse(start_time < t, offset + amplitude * cos(2 * pi * frequency * (t - start_time) + phase), offset)
  ]
  return ODESystem(eqs, t, vars, params; systems = [], name)
end
export Cosine

# Integrator
@component function Integrator(; name, x0=0, k=1)
  params = @parameters begin
    (x0::Float64 = x0), [description = "Initial value of the integrator state"]
    (k::Float64 = k), [description = "Gain"]
  end
  vars = @variables begin
    u(t), [input = true]
    y(t), [output = true]
    x(t), [description = "State of Integrator"]
  end
  initialization_eqs = [
    x ~ x0
  ]
  eqs = Equation[
    D(x) ~ k * u
    y ~ x
  ]
  return ODESystem(eqs, t, vars, params; systems = [], name, initialization_eqs)
end
export Integrator

# Cosine Test
@component function CosineTest(; name)
  systems = @named begin
    integrator = Integrator()
    signal = Cosine(amplitude=1, frequency=2, start_time=0.5, offset=0.5, phase=3.14)
  end
  eqs = Equation[
    signal.y ~ integrator.u
  ]
  return ODESystem(eqs, t, [], []; systems, name)
end
export CosineTest


## Testset for the Cosine Test
using OrdinaryDiffEqDefault
using Test

@testset "Running test case1 for CosineTest" begin

  @named model_full = CosineTest()
  # Error with IfLifting
  model = structural_simplify(model_full; additional_passes=[ModelingToolkit.IfLifting]) 
  u0 = []
  prob = ODEProblem(model, u0, (0, 5))
  sol = solve(prob, DefaultODEAlgorithm())
  @test SciMLBase.successful_retcode(sol)
  @test sol[model.signal.y][1] ≈ 0.5 atol = 0.001
  @test sol[model.signal.y][end] ≈ -0.49999 atol = 0.001
  @test sol[model.integrator.x][end] ≈ 2.45255 atol = 0.001

end

[maxesit]

I'll go through the models 1 by 1 to find the ones that error, pull one of them out and post the MWE here. I have to leave home now, so first thing in the morning!

[mtiller-jh]

All, I revisited the errors I'm seeing and I realized that the current error I'm experiencing (after resolving the issue with the macro) is the error that @maxesit has reproduced but that is actually just a failure of the regression testing. In other words, the IfLifting isn't failing before simulation (as it was before). So, my apologies to @AayushSabharwal and @BenChung for this distraction.

However, there does seem to be a different issue lurking somewhere here. With IfLifting in place, there is something strange going on with the simulations. I haven't had a chance to investigate completely but it looks like the time interval being solved is somehow changing. The final values of some variables are significantly different here and I'm getting odd errors in the interpolation saying that I'm trying to interpolate beyond the solution even though I don't see how that is possible. But this is all too vague to be actionable at the moment. So, I'm going to close this issue and I'll open a new one that focuses on these discrepancies once I convince myself I'm not doing something stupid and I have an MWE.