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Cache common subexpressions in IndexMap #2802

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0de9a46
Cache common subexpressions in IndexMap
blegat Aug 6, 2025
bbea2d7
Address review: tests, benchmark and experimental comment
blegat Nov 3, 2026
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26 changes: 26 additions & 0 deletions src/Utilities/copy/index_map.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,9 @@
typeof(CleverDicts.index_to_key),
}
con_map::DoubleDicts.IndexDoubleDict
# This field is experimental and may be removed in a future release. Do not
# access it directly; use `map_indices` instead.
nl_cache::IdDict{MOI.ScalarNonlinearFunction,MOI.ScalarNonlinearFunction}
end

"""
Expand All @@ -33,6 +36,11 @@
return IndexMap(var_map, con_map)
end

function IndexMap(var_map, con_map)
nl_cache = IdDict{MOI.ScalarNonlinearFunction,MOI.ScalarNonlinearFunction}()
return IndexMap(var_map, con_map, nl_cache)
end

function _identity_constraints_map(
model,
map::DoubleDicts.IndexDoubleDictInner{F,S},
Expand Down Expand Up @@ -121,3 +129,21 @@
end
return map_indices(Base.Fix1(getindex, map), x)
end

# Common subexpressions, i.e., `MOI.ScalarNonlinearFunction` objects that are

Check failure on line 133 in src/Utilities/copy/index_map.jl

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[vale] reported by reviewdog 🐶
[Google.Latin] Use 'that is' instead of 'i.e.,'.

Raw Output:
{"message":"[Google.Latin] Use 'that is' instead of 'i.e.,'.","location":{"path":"src/Utilities/copy/index_map.jl","range":{"start":{"line":133,"column":26},"end":{"line":133,"column":31}}},"severity":"ERROR","code":{"value":"Google.Latin","url":"https://developers.google.com/style/abbreviations"}}
# shared between functions, are mapped only once, and the mapped functions
# share the corresponding mapped subexpressions.
function map_indices(map::IndexMap, f::MOI.ScalarNonlinearFunction)
if CleverDicts.is_identity(map.var_map)
return f
end
return map_indices(Base.Fix1(getindex, map), f, map.nl_cache)
end

function map_indices(map::IndexMap, f::MOI.VectorNonlinearFunction)
if CleverDicts.is_identity(map.var_map)
return f
end
rows = MOI.ScalarNonlinearFunction[map_indices(map, row) for row in f.rows]
return MOI.VectorNonlinearFunction(rows)
end
14 changes: 14 additions & 0 deletions src/Utilities/functions.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -367,7 +367,11 @@ end
function map_indices(
index_map::F,
f::MOI.ScalarNonlinearFunction,
nl_cache = nothing,
) where {F<:Function}
if !isnothing(nl_cache) && haskey(nl_cache, f)
return nl_cache[f]
end
root = MOI.ScalarNonlinearFunction(f.head, similar(f.args))
stack = Tuple{MOI.ScalarNonlinearFunction,Int,MOI.ScalarNonlinearFunction}[]
for (i, fi) in enumerate(f.args)
Expand All @@ -380,6 +384,10 @@ function map_indices(
while !isempty(stack)
parent, i, arg = pop!(stack)
if arg isa MOI.ScalarNonlinearFunction
if !isnothing(nl_cache) && haskey(nl_cache, arg)
parent.args[i] = nl_cache[arg]
continue
end
child = MOI.ScalarNonlinearFunction(arg.head, similar(arg.args))
for (j, argj) in enumerate(arg.args)
if argj isa MOI.ScalarNonlinearFunction
Expand All @@ -389,10 +397,16 @@ function map_indices(
end
end
parent.args[i] = child
if !isnothing(nl_cache)
nl_cache[arg] = child
end
else
parent.args[i] = MOI.Utilities.map_indices(index_map, arg)
end
end
if !isnothing(nl_cache)
nl_cache[f] = root
end
return root
end

Expand Down
34 changes: 34 additions & 0 deletions test/Utilities/test_copy.jl
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Expand Up @@ -1144,6 +1144,40 @@ function test_map_indices_identity_index_map()
return
end

function test_map_indices_common_subexpressions()
x = MOI.VariableIndex.(1:2)
index_map = MOI.Utilities.IndexMap()
index_map[x[1]] = x[2]
index_map[x[2]] = x[1]
sin_x = MOI.ScalarNonlinearFunction(:sin, Any[x[1]])
f = MOI.ScalarNonlinearFunction(:+, Any[sin_x, sin_x, x[2]])
g = MOI.ScalarNonlinearFunction(:*, Any[2.0, sin_x])
f_dest = MOI.Utilities.map_indices(index_map, f)
@test f_dest ≈ MOI.ScalarNonlinearFunction(
:+,
Any[
MOI.ScalarNonlinearFunction(:sin, Any[x[2]]),
MOI.ScalarNonlinearFunction(:sin, Any[x[2]]),
x[1],
],
)
@test f_dest.args[1] === f_dest.args[2]
g_dest = MOI.Utilities.map_indices(index_map, g)
@test g_dest.args[2] === f_dest.args[1]
@test MOI.Utilities.map_indices(index_map, f) === f_dest
h = MOI.VectorNonlinearFunction([f, g])
h_dest = MOI.Utilities.map_indices(index_map, h)
@test h_dest.rows[1] === f_dest
@test h_dest.rows[2] === g_dest
# The cache is not used if the variable map is the identity.
identity_map = MOI.Utilities.IndexMap()
identity_map[x[1]] = x[1]
identity_map[x[2]] = x[2]
@test MOI.Utilities.map_indices(identity_map, f) === f
@test MOI.Utilities.map_indices(identity_map, h) === h
return
end

end # module

TestCopy.runtests()
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