Standard Library Builtin Stuff


I've been trying to investigate how the standard library works and I've found something that I don't fully understand.

It appears as if everything eventually boils down to "Builtin" stuff that's not actually declared anywhere, but just assumed to exist within the stdlib.

For example, a Bool is really just a wrapped for a Builtin.Int1.

Now I would like to know: Where do I find the declaration of this Int1? Or, even more interesting: Where do I find a list of all the Builtin types?

Thank you in advance,

Best regards, Vogel.

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Builtins generally expand to LLVM IR types and operations. The mappings are defined directly in the compiler (mostly include/swift/AST/Builtins.def and lib/AST/Builtins.cpp--for example, the Builtin.Int${N} types like Builtin.Int1 are defined via the machinery starting on line 102).


Hi, thanks for reply.

Can you explain where find implementation of Builtin.NativeObject.

I already use your answer and found that Builtin.NativeObject mapped to TheNativeObjectType (in Builtins.cpp). It maps by context ASTContext

But there is no mention TheNativeObjectType in ASTContext.cpp ASTContext.h

I try to google TheNativeObjectType in context of LLVM and did not find it.

Could you give more information where find implementation of Builtin type and operations ?


AFAIU, most if not all Builtin functions map to LLVM IR instructions, which you can look up in the LLVM language reference.

Thank you very much for your reply.

I already viewed this page and did not find definition of Builtin.NativeObject

With Respect

The type is defined here in ASTContext.h:

and in TypeNodes.def:

The actual type definition for this type is:


Thank you very much, I should have read the sources more carefully, thank you


Sorry to bother you again.

Could you tell me if I understood correctly that BuiltinNativeObjectType is just a "universal" pointer to any object?

And even somehow embarrassingly, I again could not find the implementation of Builtin functions, for example cancel.

I find only a '.def' file in which most of the functions I'm interested in are wrapped in BUILTIN_MISC_OPERATION_WITH_SILGEN, but the description of what does (and what is it) this is completely incomprehensible to me

Judging by the description, these functions should be generated at the SIL stage, I tried to look at the implementation of the cancel method, generated SIL and got

// Task.cancel()

sil [available 12.0.0] @$sScT6cancelyyF : $@convention(method) <τ_0_0, τ_0_1 where τ_0_0 : Sendable, τ_0_1 : Error> (@guaranteed Task<τ_0_0, τ_0_1>) -> ()

which does not give any ideas for further steps

1 Like

Task.cancel is not a builtin:

First go to Task.swift and find cancel:

  public func cancel() {

find that function in the same file:

@available(SwiftStdlib 5.1, *)
public func _taskCancel(_ task: Builtin.NativeObject)

Then find:

static void swift_task_cancelImpl(AsyncTask *task)

in TaskStatus.cpp.

Builtins like creating groups etc are declared in Builtins.def

BUILTIN_MISC_OPERATION_WITH_SILGEN(GetCurrentExecutor, "getCurrentExecutor", "", Special)

and then the signature is in Builtins.cpp:

  case BuiltinValueKind::GetCurrentExecutor:
    return getGetCurrentExecutor(Context, Id);

and implementation in GenBuiltin.cpp:

  // emitGetCurrentExecutor has no arguments.
  if (Builtin.ID == BuiltinValueKind::GetCurrentExecutor) {
    emitGetCurrentExecutor(IGF, out);

The above emit forms a call to a runtime function, which eventually ends up in plain runtime function (declared in RuntimeFunctions.def):

static SerialExecutorRef swift_task_getCurrentExecutorImpl() { ... }

Basically keep looking where GetCurrentExecutor is used, and you'll find all important places -- there's quite a few.

Hope this helps,