1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Handles codegen of callees as well as other call-related
12 //! things. Callees are a superset of normal rust values and sometimes
13 //! have different representations. In particular, top-level fn items
14 //! and methods are represented as just a fn ptr and not a full
18 use common::{self, CodegenCx};
22 use monomorphize::Instance;
23 use type_of::LayoutLlvmExt;
26 use rustc::hir::def_id::DefId;
27 use rustc::ty::{self, TypeFoldable};
28 use rustc::ty::layout::LayoutOf;
29 use rustc::ty::subst::Substs;
31 /// Codegens a reference to a fn/method item, monomorphizing and
32 /// inlining as it goes.
36 /// - `cx`: the crate context
37 /// - `instance`: the instance to be instantiated
39 cx: &CodegenCx<'ll, 'tcx>,
40 instance: Instance<'tcx>,
44 debug!("get_fn(instance={:?})", instance);
46 assert!(!instance.substs.needs_infer());
47 assert!(!instance.substs.has_escaping_regions());
48 assert!(!instance.substs.has_param_types());
50 let fn_ty = instance.ty(cx.tcx);
51 if let Some(&llfn) = cx.instances.borrow().get(&instance) {
55 let sym = tcx.symbol_name(instance).as_str();
56 debug!("get_fn({:?}: {:?}) => {}", instance, fn_ty, sym);
58 // Create a fn pointer with the substituted signature.
59 let fn_ptr_ty = tcx.mk_fn_ptr(common::ty_fn_sig(cx, fn_ty));
60 let llptrty = cx.layout_of(fn_ptr_ty).llvm_type(cx);
62 let llfn = if let Some(llfn) = declare::get_declared_value(cx, &sym) {
63 // This is subtle and surprising, but sometimes we have to bitcast
64 // the resulting fn pointer. The reason has to do with external
65 // functions. If you have two crates that both bind the same C
66 // library, they may not use precisely the same types: for
67 // example, they will probably each declare their own structs,
68 // which are distinct types from LLVM's point of view (nominal
71 // Now, if those two crates are linked into an application, and
72 // they contain inlined code, you can wind up with a situation
73 // where both of those functions wind up being loaded into this
74 // application simultaneously. In that case, the same function
75 // (from LLVM's point of view) requires two types. But of course
76 // LLVM won't allow one function to have two types.
78 // What we currently do, therefore, is declare the function with
79 // one of the two types (whichever happens to come first) and then
80 // bitcast as needed when the function is referenced to make sure
81 // it has the type we expect.
83 // This can occur on either a crate-local or crate-external
84 // reference. It also occurs when testing libcore and in some
85 // other weird situations. Annoying.
86 if common::val_ty(llfn) != llptrty {
87 debug!("get_fn: casting {:?} to {:?}", llfn, llptrty);
88 consts::ptrcast(llfn, llptrty)
90 debug!("get_fn: not casting pointer!");
94 let llfn = declare::declare_fn(cx, &sym, fn_ty);
95 assert_eq!(common::val_ty(llfn), llptrty);
96 debug!("get_fn: not casting pointer!");
98 if instance.def.is_inline(tcx) {
99 attributes::inline(llfn, attributes::InlineAttr::Hint);
101 attributes::from_fn_attrs(cx, llfn, instance.def.def_id());
103 let instance_def_id = instance.def_id();
105 // Apply an appropriate linkage/visibility value to our item that we
108 // This is sort of subtle. Inside our codegen unit we started off
109 // compilation by predefining all our own `MonoItem` instances. That
110 // is, everything we're codegenning ourselves is already defined. That
111 // means that anything we're actually codegenning in this codegen unit
112 // will have hit the above branch in `get_declared_value`. As a result,
113 // we're guaranteed here that we're declaring a symbol that won't get
114 // defined, or in other words we're referencing a value from another
115 // codegen unit or even another crate.
117 // So because this is a foreign value we blanket apply an external
118 // linkage directive because it's coming from a different object file.
119 // The visibility here is where it gets tricky. This symbol could be
120 // referencing some foreign crate or foreign library (an `extern`
121 // block) in which case we want to leave the default visibility. We may
122 // also, though, have multiple codegen units. It could be a
123 // monomorphization, in which case its expected visibility depends on
124 // whether we are sharing generics or not. The important thing here is
125 // that the visibility we apply to the declaration is the same one that
126 // has been applied to the definition (wherever that definition may be).
128 llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
130 let is_generic = instance.substs.types().next().is_some();
133 // This is a monomorphization. Its expected visibility depends
134 // on whether we are in share-generics mode.
136 if cx.tcx.sess.opts.share_generics() {
137 // We are in share_generics mode.
139 if instance_def_id.is_local() {
140 // This is a definition from the current crate. If the
141 // definition is unreachable for downstream crates or
142 // the current crate does not re-export generics, the
143 // definition of the instance will have been declared
145 if cx.tcx.is_unreachable_local_definition(instance_def_id) ||
146 !cx.tcx.local_crate_exports_generics() {
147 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
150 // This is a monomorphization of a generic function
151 // defined in an upstream crate.
152 if cx.tcx.upstream_monomorphizations_for(instance_def_id)
153 .map(|set| set.contains_key(instance.substs))
155 // This is instantiated in another crate. It cannot
158 // This is a local instantiation of an upstream definition.
159 // If the current crate does not re-export it
160 // (because it is a C library or an executable), it
161 // will have been declared `hidden`.
162 if !cx.tcx.local_crate_exports_generics() {
163 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
168 // When not sharing generics, all instances are in the same
169 // crate and have hidden visibility
170 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
173 // This is a non-generic function
174 if cx.tcx.is_codegened_item(instance_def_id) {
175 // This is a function that is instantiated in the local crate
177 if instance_def_id.is_local() {
178 // This is function that is defined in the local crate.
179 // If it is not reachable, it is hidden.
180 if !cx.tcx.is_reachable_non_generic(instance_def_id) {
181 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
184 // This is a function from an upstream crate that has
185 // been instantiated here. These are always hidden.
186 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
192 if cx.use_dll_storage_attrs &&
193 tcx.is_dllimport_foreign_item(instance_def_id)
196 llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
203 cx.instances.borrow_mut().insert(instance, llfn);
208 pub fn resolve_and_get_fn(
209 cx: &CodegenCx<'ll, 'tcx>,
211 substs: &'tcx Substs<'tcx>,
215 ty::Instance::resolve(
217 ty::ParamEnv::reveal_all(),