compiler/rustc_codegen_gcc/src/callee.rs

#[cfg(feature="master")]
use gccjit::{FnAttribute, Visibility};
use gccjit::{FunctionType, Function};
use rustc_middle::ty::{self, Instance, TypeVisitableExt};
use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt};

use crate::attributes;
use crate::context::CodegenCx;

/// Codegens a reference to a fn/method item, monomorphizing and
/// inlining as it goes.
///
/// # Parameters
///
/// - `cx`: the crate context
/// - `instance`: the instance to be instantiated
pub fn get_fn<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, instance: Instance<'tcx>) -> Function<'gcc> {
    let tcx = cx.tcx();

    assert!(!instance.substs.has_infer());
    assert!(!instance.substs.has_escaping_bound_vars());

    let sym = tcx.symbol_name(instance).name;

    if let Some(&func) = cx.function_instances.borrow().get(&instance) {
        return func;
    }

    let fn_abi = cx.fn_abi_of_instance(instance, ty::List::empty());

    let func =
        if let Some(_func) = cx.get_declared_value(&sym) {
            // FIXME(antoyo): we never reach this because get_declared_value only returns global variables
            // and here we try to get a function.
            unreachable!();
            /*
            // Create a fn pointer with the new signature.
            let ptrty = fn_abi.ptr_to_gcc_type(cx);

            // This is subtle and surprising, but sometimes we have to bitcast
            // the resulting fn pointer.  The reason has to do with external
            // functions.  If you have two crates that both bind the same C
            // library, they may not use precisely the same types: for
            // example, they will probably each declare their own structs,
            // which are distinct types from LLVM's point of view (nominal
            // types).
            //
            // Now, if those two crates are linked into an application, and
            // they contain inlined code, you can wind up with a situation
            // where both of those functions wind up being loaded into this
            // application simultaneously. In that case, the same function
            // (from LLVM's point of view) requires two types. But of course
            // LLVM won't allow one function to have two types.
            //
            // What we currently do, therefore, is declare the function with
            // one of the two types (whichever happens to come first) and then
            // bitcast as needed when the function is referenced to make sure
            // it has the type we expect.
            //
            // This can occur on either a crate-local or crate-external
            // reference. It also occurs when testing libcore and in some
            // other weird situations. Annoying.
            if cx.val_ty(func) != ptrty {
                // TODO(antoyo): cast the pointer.
                func
            }
            else {
                func
            }*/
        }
        else {
            cx.linkage.set(FunctionType::Extern);
            let func = cx.declare_fn(&sym, &fn_abi);

            attributes::from_fn_attrs(cx, func, instance);

            let instance_def_id = instance.def_id();

            // TODO(antoyo): set linkage and attributes.

            // Apply an appropriate linkage/visibility value to our item that we
            // just declared.
            //
            // This is sort of subtle. Inside our codegen unit we started off
            // compilation by predefining all our own `MonoItem` instances. That
            // is, everything we're codegenning ourselves is already defined. That
            // means that anything we're actually codegenning in this codegen unit
            // will have hit the above branch in `get_declared_value`. As a result,
            // we're guaranteed here that we're declaring a symbol that won't get
            // defined, or in other words we're referencing a value from another
            // codegen unit or even another crate.
            //
            // So because this is a foreign value we blanket apply an external
            // linkage directive because it's coming from a different object file.
            // The visibility here is where it gets tricky. This symbol could be
            // referencing some foreign crate or foreign library (an `extern`
            // block) in which case we want to leave the default visibility. We may
            // also, though, have multiple codegen units. It could be a
            // monomorphization, in which case its expected visibility depends on
            // whether we are sharing generics or not. The important thing here is
            // that the visibility we apply to the declaration is the same one that
            // has been applied to the definition (wherever that definition may be).
            let is_generic = instance.substs.non_erasable_generics().next().is_some();

            if is_generic {
                // This is a monomorphization. Its expected visibility depends
                // on whether we are in share-generics mode.

                if cx.tcx.sess.opts.share_generics() {
                    // We are in share_generics mode.

                    if let Some(instance_def_id) = instance_def_id.as_local() {
                        // This is a definition from the current crate. If the
                        // definition is unreachable for downstream crates or
                        // the current crate does not re-export generics, the
                        // definition of the instance will have been declared
                        // as `hidden`.
                        if cx.tcx.is_unreachable_local_definition(instance_def_id)
                            || !cx.tcx.local_crate_exports_generics()
                        {
                            #[cfg(feature="master")]
                            func.add_attribute(FnAttribute::Visibility(Visibility::Hidden));
                        }
                    } else {
                        // This is a monomorphization of a generic function
                        // defined in an upstream crate.
                        if instance.upstream_monomorphization(tcx).is_some() {
                            // This is instantiated in another crate. It cannot
                            // be `hidden`.
                        } else {
                            // This is a local instantiation of an upstream definition.
                            // If the current crate does not re-export it
                            // (because it is a C library or an executable), it
                            // will have been declared `hidden`.
                            if !cx.tcx.local_crate_exports_generics() {
                                #[cfg(feature="master")]
                                func.add_attribute(FnAttribute::Visibility(Visibility::Hidden));
                            }
                        }
                    }
                } else {
                    // When not sharing generics, all instances are in the same
                    // crate and have hidden visibility
                    #[cfg(feature="master")]
                    func.add_attribute(FnAttribute::Visibility(Visibility::Hidden));
                }
            } else {
                // This is a non-generic function
                if cx.tcx.is_codegened_item(instance_def_id) {
                    // This is a function that is instantiated in the local crate

                    if instance_def_id.is_local() {
                        // This is function that is defined in the local crate.
                        // If it is not reachable, it is hidden.
                        if !cx.tcx.is_reachable_non_generic(instance_def_id) {
                            #[cfg(feature="master")]
                            func.add_attribute(FnAttribute::Visibility(Visibility::Hidden));
                        }
                    } else {
                        // This is a function from an upstream crate that has
                        // been instantiated here. These are always hidden.
                        #[cfg(feature="master")]
                        func.add_attribute(FnAttribute::Visibility(Visibility::Hidden));
                    }
                }
            }

            func
        };

    cx.function_instances.borrow_mut().insert(instance, func);

    func
}