fix double-counting and non-deterministic results in summarysize

fixes #53061

Co-authored-by: Orestis Ousoultzoglou <[email protected]>

Author: JeffBezanson

base/reflection.jl

@@ -529,6 +529,17 @@ function datatype_nfields(dt::DataType)
     return unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).nfields
 end
 
+"""
+    Base.datatype_npointers(dt::DataType) -> Int
+
+Return the number of pointers in the layout of a datatype.
+"""
+function datatype_npointers(dt::DataType)
+    @_foldable_meta
+    dt.layout == C_NULL && throw(UndefRefError())
+    return unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).npointers
+end
+
 """
     Base.datatype_pointerfree(dt::DataType) -> Bool
 
@@ -537,9 +548,7 @@ Can be called on any `isconcretetype`.
 """
 function datatype_pointerfree(dt::DataType)
     @_foldable_meta
-    dt.layout == C_NULL && throw(UndefRefError())
-    npointers = unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).npointers
-    return npointers == 0
+    return datatype_npointers(dt) == 0
 end
 
 """

base/summarysize.jl

@@ -8,6 +8,9 @@ struct SummarySize
     chargeall::Any
 end
 
+nth_pointer_isdefined(obj, i::Int) = ccall(:jl_nth_pointer_isdefined, Cint, (Any, Csize_t), obj, i-1) != 0
+get_nth_pointer(obj, i::Int) = ccall(:jl_get_nth_pointer, Any, (Any, Csize_t), obj, i-1)
+
 """
     Base.summarysize(obj; exclude=Union{...}, chargeall=Union{...}) -> Int
 
@@ -26,7 +29,7 @@ julia> Base.summarysize(1.0)
 8
 
 julia> Base.summarysize(Ref(rand(100)))
-864
+848
 
 julia> sizeof(Ref(rand(100)))
 8
@@ -50,15 +53,28 @@ function summarysize(obj;
                 val = x[i]
             end
         elseif isa(x, GenericMemory)
-            nf = length(x)
-            if @inbounds @inline isassigned(x, i)
-                val = x[i]
+            T = eltype(x)
+            if Base.allocatedinline(T)
+                np = datatype_npointers(T)
+                nf = length(x) * np
+                idx = (i-1) ÷ np + 1
+                if @inbounds @inline isassigned(x, idx)
+                    elt = x[idx]
+                    p = (i-1) % np + 1
+                    if nth_pointer_isdefined(elt, p)
+                        val = get_nth_pointer(elt, p)
+                    end
+                end
+            else
+                nf = length(x)
+                if @inbounds @inline isassigned(x, i)
+                    val = x[i]
+                end
             end
         else
-            nf = nfields(x)
-            ft = typeof(x).types
-            if !isbitstype(ft[i]) && isdefined(x, i)
-                val = getfield(x, i)
+            nf = datatype_npointers(typeof(x))
+            if nth_pointer_isdefined(x, i)
+                val = get_nth_pointer(x, i)
             end
         end
         if nf > i
@@ -82,7 +98,7 @@ end
     # and so is somewhat approximate.
     key = ccall(:jl_value_ptr, Ptr{Cvoid}, (Any,), obj)
     haskey(ss.seen, key) ? (return 0) : (ss.seen[key] = true)
-    if nfields(obj) > 0
+    if datatype_npointers(typeof(obj)) > 0
         push!(ss.frontier_x, obj)
         push!(ss.frontier_i, 1)
     end

src/datatype.c

@@ -2253,6 +2253,39 @@ JL_DLLEXPORT size_t jl_get_field_offset(jl_datatype_t *ty, int field)
     return jl_field_offset(ty, field - 1);
 }
 
+jl_value_t *get_nth_pointer(jl_value_t *v, size_t i)
+{
+    jl_datatype_t *dt = (jl_datatype_t*)jl_typeof(v);
+    const jl_datatype_layout_t *ly = dt->layout;
+    uint32_t npointers = ly->npointers;
+    if (i >= npointers)
+        jl_bounds_error_int(v, i);
+    const uint8_t *ptrs8 = (const uint8_t *)jl_dt_layout_ptrs(ly);
+    const uint16_t *ptrs16 = (const uint16_t *)jl_dt_layout_ptrs(ly);
+    const uint32_t *ptrs32 = (const uint32_t*)jl_dt_layout_ptrs(ly);
+    uint32_t fld;
+    if (ly->flags.fielddesc_type == 0)
+        fld = ptrs8[i];
+    else if (ly->flags.fielddesc_type == 1)
+        fld = ptrs16[i];
+    else
+        fld = ptrs32[i];
+    return ((jl_value_t**)v)[fld];
+}
+
+JL_DLLEXPORT jl_value_t *jl_get_nth_pointer(jl_value_t *v, size_t i)
+{
+    jl_value_t *ptrf = get_nth_pointer(v, i);
+    if (__unlikely(ptrf == NULL))
+        jl_throw(jl_undefref_exception);
+    return ptrf;
+}
+
+JL_DLLEXPORT int jl_nth_pointer_isdefined(jl_value_t *v, size_t i)
+{
+    return get_nth_pointer(v, i) != NULL;
+}
+
 #ifdef __cplusplus
 }
 #endif

test/misc.jl

@@ -573,6 +573,23 @@ end
 # issue #44780
 @test summarysize(BigInt(2)^1000) > summarysize(BigInt(2))
 
+# issue #53061
+mutable struct S53061
+    x::Union{Float64, Tuple{Float64, Float64}}
+    y::Union{Float64, Tuple{Float64, Float64}}
+end
+let s = S53061[S53061(rand(), (rand(),rand())) for _ in 1:10^4]
+    @test allequal(summarysize(s) for i in 1:10)
+end
+struct Z53061
+    x::S53061
+    y::Int64
+end
+let z = Z53061[Z53061(S53061(rand(), (rand(),rand())), 0) for _ in 1:10^4]
+    @test allequal(summarysize(z) for i in 1:10)
+    @test abs(summarysize(z) - 640000)/640000 <= 0.01
+end
+
 ## test conversion from UTF-8 to UTF-16 (for Windows APIs)
 
 # empty arrays