Comments (10)
ChrisRackauckas
commented on August 17, 2024
This is not a good test case for it. Or at least the title is not correct. Julia's dead code elimination is performed at the lock level. So if you want to determine what code is actually run you need to check the post optimization llvm. But llvm's dce is very robust so I would be surprised if there is a problem there.
Now your example would not dce because your code mutates a global and thus the compiler is not allowed to delete that as it would clearly change the code behavior. So your test case, if changed to not have a side effect, would get erased in the llvm layer
But finally, it isn't optimal to drop all of the observed in there and rely on dce. While it would make 0 difference in runtime, it could make a difference in compile time. It would be good to actually measure that and see if it's an noticable effect. Since dce is prior to the most expensive passes I would be surprised if that was the case though
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ctessum
commented on August 17, 2024
Does this work as a test case:
function f(t)
@info "evaluating unnecessary observed function"
return sin(t)
endIt gives a similar result, printing 9 lines of log messages.
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ChrisRackauckas
commented on August 17, 2024
No, logging is again mutating a global so DCE is not allowed to delete it since it would change how code is run. It would have to be something like
julia> function f(t)
a = 1+1
return sin(t)
end
f (generic function with 1 method)
julia> @code_llvm(f(1.0))
; @ REPL[4]:1 within `f`
; Function Attrs: uwtable
define double @julia_f_1898(double %0) #0 {
top:
; @ REPL[4]:3 within `f`
%1 = call double @j_sin_1900(double %0)
ret double %1
}You can see DCE removed the extraneous computation in the LLVM.
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ctessum
commented on August 17, 2024
OK, I see the miscommunication here. The problem that I have is not that there is extraneous code running in the function, it's that that function is running at all. So, in other words, the desired behavior in this case would be that f(t) is never called, because the variable on the right-hand-side of that equation, y, is never used for anything.
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ChrisRackauckas
commented on August 17, 2024
That will be deleted by DCE though, so it won't be actually called. Can you show me the LLVM where it's called and it's not needed?
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ctessum
commented on August 17, 2024
using ModelingToolkit, DifferentialEquations
using ModelingToolkit: t_nounits as t, D_nounits as D
using Test
using InteractiveUtils
@variables x(t)=1 y(t)=1
function f(t)
return sin(t)
end
@register_symbolic f(t)
@named sys = ODESystem([
D(x) ~ 1,
y ~ f(t)
], t)
sys = structural_simplify(sys)
prob = ODEProblem(sys, [], (0.0, 1.0), [])
@code_llvm(prob.f([0.0, 0.0], 0.0, 0.0)); @ within `ODEFunction`
define nonnull {}* @julia_ODEFunction_3351({ [1 x i8], { { i64, {}*, { {}*, i8, {}*, {}*, {}*, {}*, {}*, i32 }, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, i8, {}*, {}*, {}*, {}*, {}* }, {}*, i8, i8, {}* }, { i64, {}*, { {}*, i8, {}*, {}*, {}*, {}*, {}*, i32 }, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, i8, {}*, {}*, {}*, {}*, {}* } }* nocapture noundef nonnull readonly align 8 dereferenceable(736) %0, {}* noundef nonnull align 16 dereferenceable(40) %1, double %2, double %3) #0 {
top:
; ┌ @ .julia/packages/ModelingToolkit/3AmNp/src/systems/diffeqs/abstractodesystem.jl:335 within `f`
; │┌ @/.julia/packages/RuntimeGeneratedFunctions/M9ZX8/src/RuntimeGeneratedFunctions.jl:150 within `RuntimeGeneratedFunction`
; ││┌ @ none within `generated_callfunc`
; │││┌ @ none within `macro expansion` @ /RuntimeGeneratedFunctions/M9ZX8/src/RuntimeGeneratedFunctions.jl:163 @ .julia/packages/SymbolicUtils/EGhOJ/src/code.jl:375
; ││││┌ @ /test.jl:8 within `f`
%4 = call double @j_sin_3353(double %2)
; ││││└
; ││││ @ none within `macro expansion` @ /.julia/packages/RuntimeGeneratedFunctions/M9ZX8/src/RuntimeGeneratedFunctions.jl:163 @ /.julia/packages/SymbolicUtils/EGhOJ/src/code.jl:468
; ││││┌ @ /.julia/packages/SymbolicUtils/EGhOJ/src/code.jl:498 within `create_array`
; │││││┌ @ array.jl:163 within `vect`
; ││││││┌ @ boot.jl:477 within `Array`
%5 = call nonnull {}* inttoptr (i64 4315363904 to {}* ({}*, i64)*)({}* inttoptr (i64 4762507712 to {}*), i64 1)
; ││││││└
; ││││││ @ array.jl:165 within `vect`
; ││││││┌ @ array.jl:1026 within `__inbounds_setindex!`
%6 = bitcast {}* %5 to double**
%arrayptr4 = load double*, double** %6, align 8
store double 1.000000e+00, double* %arrayptr4, align 8
; ││││└└└
; ││││ @ none within `macro expansion`
ret {}* %5
; └└└└from modelingtoolkit.jl.
ctessum
commented on August 17, 2024
It's the %4 = call double @j_sin_3353(double %2), right?
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ChrisRackauckas
commented on August 17, 2024
Try @code_llvm optimize=true f(x)
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ctessum
commented on August 17, 2024
Still there:
@code_llvm optimize=true prob.f([0.0, 0.0], 0.0, 0.0) @ //.julia/packages/SciMLBase/hq1ku/src/scimlfunctions.jl:2299 within `ODEFunction`
define nonnull {}* @julia_ODEFunction_2895({ [1 x i8], { { i64, {}*, { {}*, i8, {}*, {}*, {}*, {}*, {}*, i32 }, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, i8, {}*, {}*, {}*, {}*, {}* }, {}*, i8, i8, {}* }, { i64, {}*, { {}*, i8, {}*, {}*, {}*, {}*, {}*, i32 }, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, {}*, i8, {}*, {}*, {}*, {}*, {}* } }* nocapture noundef nonnull readonly align 8 dereferenceable(736) %0, {}* noundef nonnull align 16 dereferenceable(40) %1, double %2, double %3) #0 {
top:
; ┌ @ /.julia/packages/ModelingToolkit/3AmNp/src/systems/diffeqs/abstractodesystem.jl:335 within `f`
; │┌ @ /.julia/packages/RuntimeGeneratedFunctions/M9ZX8/src/RuntimeGeneratedFunctions.jl:150 within `RuntimeGeneratedFunction`
; ││┌ @ none within `generated_callfunc`
; │││┌ @ none within `macro expansion` @ //.julia/packages/RuntimeGeneratedFunctions/M9ZX8/src/RuntimeGeneratedFunctions.jl:163 @ /.julia/packages/SymbolicUtils/EGhOJ/src/code.jl:375
; ││││┌ @ /test.jl:9 within `f`
%4 = call double @j_sin_2897(double %2)
; ││││└
; ││││ @ none within `macro expansion` @ /.julia/packages/RuntimeGeneratedFunctions/M9ZX8/src/RuntimeGeneratedFunctions.jl:163 @ /.julia/packages/SymbolicUtils/EGhOJ/src/code.jl:468
; ││││┌ @ /.julia/packages/SymbolicUtils/EGhOJ/src/code.jl:498 within `create_array`
; │││││┌ @ array.jl:163 within `vect`
; ││││││┌ @ boot.jl:477 within `Array`
%5 = call nonnull {}* inttoptr (i64 4353620544 to {}* ({}*, i64)*)({}* inttoptr (i64 4800764352 to {}*), i64 1)
; ││││││└
; ││││││ @ array.jl:165 within `vect`
; ││││││┌ @ array.jl:1026 within `__inbounds_setindex!`
%6 = bitcast {}* %5 to double**
%arrayptr4 = load double*, double** %6, align 8
store double 1.000000e+00, double* %arrayptr4, align 8
; ││││└└└
; ││││ @ none within `macro expansion`
ret {}* %5
; └└└└
}from modelingtoolkit.jl.
ChrisRackauckas
commented on August 17, 2024
@gbaraldi is this because we cannot prove sin doesn't have side effects? I thought the effects system would have solved that?
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Related Issues (20)
- Optimizing a control signal
- undefvar and bounds error in linearization_function
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