arrayunset: micro-optimization for performance (#32405)

Author: vtjnash

base/array.jl

@@ -175,6 +175,20 @@ false
 isbitsunion(u::Union) = (@_pure_meta; ccall(:jl_array_store_unboxed, Cint, (Any,), u) != Cint(0))
 isbitsunion(x) = false
 
+isptrelement(t::Type) = (@_pure_meta; ccall(:jl_array_store_unboxed, Cint, (Any,), t) == Cint(0))
+
+function _unsetindex!(A::Array{T}, i::Int) where {T}
+    @boundscheck checkbounds(A, i)
+    if isptrelement(T)
+        t = @_gc_preserve_begin A
+        p = Ptr{Ptr{Cvoid}}(pointer(A))
+        unsafe_store!(p, C_NULL, i)
+        @_gc_preserve_end t
+    end
+    return A
+end
+
+
 """
     Base.bitsunionsize(U::Union)
 

base/dict.jl

@@ -620,8 +620,8 @@ end
 
 function _delete!(h::Dict{K,V}, index) where {K,V}
     @inbounds h.slots[index] = 0x2
-    isbitstype(K) || isbitsunion(K) || ccall(:jl_arrayunset, Cvoid, (Any, UInt), h.keys, index-1)
-    isbitstype(V) || isbitsunion(V) || ccall(:jl_arrayunset, Cvoid, (Any, UInt), h.vals, index-1)
+    @inbounds _unsetindex!(h.keys, index)
+    @inbounds _unsetindex!(h.vals, index)
     h.ndel += 1
     h.count -= 1
     h.age += 1

src/array.c

@@ -592,10 +592,9 @@ JL_DLLEXPORT void jl_arrayset(jl_array_t *a JL_ROOTING_ARGUMENT, jl_value_t *rhs
 JL_DLLEXPORT void jl_arrayunset(jl_array_t *a, size_t i)
 {
     if (i >= jl_array_len(a))
-        jl_bounds_error_int((jl_value_t*)a, i+1);
-    char *ptail = (char*)a->data + i*a->elsize;
+        jl_bounds_error_int((jl_value_t*)a, i + 1);
     if (a->flags.ptrarray)
-        memset(ptail, 0, a->elsize);
+        ((jl_value_t**)a->data)[i] = NULL;
 }
 
 // at this size and bigger, allocate resized array data with malloc