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Changes __traits(getPointerBitmap, S) for types without pointers to return size only #22289

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Changes __traits(getPointerBitmap, S) for types without pointers to return size only #22289

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b030b68
Optimize `getTypePointerBitmap` for large static arrays without point…
JohanEngelen Dec 22, 2025
b13511e
Changes `__traits(getPointerBitmap, S)` for types without pointers to…
JohanEngelen Dec 22, 2025
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3 changes: 2 additions & 1 deletion compiler/src/dmd/glue/toobj.d
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Original file line number Diff line number Diff line change
Expand Up @@ -119,7 +119,8 @@ void write_instance_pointers(Type type, Symbol* s, uint offset)
return;

Array!(ulong) data;
const ulong sz = getTypePointerBitmap(Loc.initial, type, data, global.errorSink);
ulong count;
const ulong sz = getTypePointerBitmap(Loc.initial, type, data, global.errorSink, count);
if (sz == ulong.max)
return;

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26 changes: 20 additions & 6 deletions compiler/src/dmd/traits.d
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Original file line number Diff line number Diff line change
Expand Up @@ -99,10 +99,11 @@ private Dsymbol getDsymbolWithoutExpCtx(RootObject oarg)
* t = type to generate pointer bitmap from
* data = array forming the bitmap
* eSink = error message sink
* count = returns the number of bits set in the bitmap (i.e. the number of pointers)
* Returns:
* size of the type `t` in bytes, ulong.max on error
*/
ulong getTypePointerBitmap(Loc loc, Type t, ref Array!(ulong) data, ErrorSink eSink)
ulong getTypePointerBitmap(Loc loc, Type t, ref Array!(ulong) data, ErrorSink eSink, out ulong count)
{
auto tc = t.isTypeClass();
const ulong sz = (tc && !tc.sym.isInterfaceDeclaration())
Expand Down Expand Up @@ -133,6 +134,7 @@ ulong getTypePointerBitmap(Loc loc, Type t, ref Array!(ulong) data, ErrorSink eS
{
void setpointer(ulong off)
{
count++;
ulong ptroff = off / sz_size_t;
data[cast(size_t)(ptroff / bitsPerElement)] |= 1L << (ptroff % bitsPerElement);
}
Expand Down Expand Up @@ -165,11 +167,14 @@ ulong getTypePointerBitmap(Loc loc, Type t, ref Array!(ulong) data, ErrorSink eS
ulong nextsize = t.next.size();
if (nextsize == SIZE_INVALID)
error = true;
ulong dim = t.dim.toInteger();
for (ulong i = 0; i < dim; i++)
if (t.hasPointers)
{
offset = arrayoff + i * nextsize;
visit(t.next);
ulong dim = t.dim.toInteger();
for (ulong i = 0; i < dim; i++)
{
offset = arrayoff + i * nextsize;
visit(t.next);
}
}
offset = arrayoff;
}
Expand Down Expand Up @@ -286,6 +291,7 @@ ulong getTypePointerBitmap(Loc loc, Type t, ref Array!(ulong) data, ErrorSink eS
* architecture). If set the corresponding memory might contain a pointer/reference.
*
* Returns: [T.sizeof, pointerbit0-31/63, pointerbit32/64-63/128, ...]
* OR: [T.sizeof] if the type contains no pointers
*/
private Expression pointerBitmap(TraitsExp e, ErrorSink eSink)
{
Expand All @@ -303,10 +309,18 @@ private Expression pointerBitmap(TraitsExp e, ErrorSink eSink)
}

Array!(ulong) data;
const ulong sz = getTypePointerBitmap(e.loc, t, data, eSink);
ulong count;
const ulong sz = getTypePointerBitmap(e.loc, t, data, eSink, count);
if (sz == ulong.max)
return ErrorExp.get();

if (count == 0)
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@rainers rainers Dec 26, 2025

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Checking t.hasPointers() instead would allow moving this section before the call to getTypePointerBitmap and avoid any counting.

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@JohanEngelen JohanEngelen Dec 27, 2025

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true, but then there is a perf hit for when hasPointers is true (you'd have to traverse the type ast twice)

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@rainers rainers Dec 29, 2025

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hasPointers is only a traversal for structs and these cache that information. As the hasPointers or any other method calling determineTypeProperties is very likely to be called anyway before/after, I don't expect much performance penalty. I don't mind that much keeping count as is, though.

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@JohanEngelen JohanEngelen Dec 29, 2025

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OK, then better to change it to hasPointers. The count thing is a little ugly, I find.

{
auto exps = new Expressions(1);
(*exps)[0] = new IntegerExp(e.loc, sz, Type.tsize_t);
return new ArrayLiteralExp(e.loc, Type.tsize_t.sarrayOf(1), exps);
}

auto exps = new Expressions(data.length + 1);
(*exps)[0] = new IntegerExp(e.loc, sz, Type.tsize_t); // [0] is size in bytes of t
foreach (size_t i; 1 .. exps.length)
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2 changes: 1 addition & 1 deletion druntime/src/object.d
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Expand Up @@ -3757,7 +3757,7 @@ template RTInfoImpl(size_t[] pointerBitmap)
template RTInfo(T)
{
enum pointerBitmap = __traits(getPointerBitmap, T);
static if (pointerBitmap[1 .. $] == size_t[pointerBitmap.length - 1].init)
static if (pointerBitmap.length == 1)
enum RTInfo = rtinfoNoPointers;
else
enum RTInfo = RTInfoImpl!(pointerBitmap).ptr;
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