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 translation 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};
21 use llvm::{self, ValueRef};
22 use monomorphize::Instance;
23 use type_of::LayoutLlvmExt;
25 use rustc::hir::def_id::DefId;
26 use rustc::ty::{self, TypeFoldable};
27 use rustc::ty::layout::LayoutOf;
29 use rustc::ty::subst::Substs;
30 use rustc_back::PanicStrategy;
32 /// Translates a reference to a fn/method item, monomorphizing and
33 /// inlining as it goes.
37 /// - `cx`: the crate context
38 /// - `instance`: the instance to be instantiated
39 pub fn get_fn<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
40 instance: Instance<'tcx>)
45 debug!("get_fn(instance={:?})", instance);
47 assert!(!instance.substs.needs_infer());
48 assert!(!instance.substs.has_escaping_regions());
49 assert!(!instance.substs.has_param_types());
51 let fn_ty = instance.ty(cx.tcx);
52 if let Some(&llfn) = cx.instances.borrow().get(&instance) {
56 let sym = tcx.symbol_name(instance);
57 debug!("get_fn({:?}: {:?}) => {}", instance, fn_ty, sym);
59 // Create a fn pointer with the substituted signature.
60 let fn_ptr_ty = tcx.mk_fn_ptr(common::ty_fn_sig(cx, fn_ty));
61 let llptrty = cx.layout_of(fn_ptr_ty).llvm_type(cx);
63 let llfn = if let Some(llfn) = declare::get_declared_value(cx, &sym) {
64 // This is subtle and surprising, but sometimes we have to bitcast
65 // the resulting fn pointer. The reason has to do with external
66 // functions. If you have two crates that both bind the same C
67 // library, they may not use precisely the same types: for
68 // example, they will probably each declare their own structs,
69 // which are distinct types from LLVM's point of view (nominal
72 // Now, if those two crates are linked into an application, and
73 // they contain inlined code, you can wind up with a situation
74 // where both of those functions wind up being loaded into this
75 // application simultaneously. In that case, the same function
76 // (from LLVM's point of view) requires two types. But of course
77 // LLVM won't allow one function to have two types.
79 // What we currently do, therefore, is declare the function with
80 // one of the two types (whichever happens to come first) and then
81 // bitcast as needed when the function is referenced to make sure
82 // it has the type we expect.
84 // This can occur on either a crate-local or crate-external
85 // reference. It also occurs when testing libcore and in some
86 // other weird situations. Annoying.
87 if common::val_ty(llfn) != llptrty {
88 debug!("get_fn: casting {:?} to {:?}", llfn, llptrty);
89 consts::ptrcast(llfn, llptrty)
91 debug!("get_fn: not casting pointer!");
95 let llfn = declare::declare_fn(cx, &sym, fn_ty);
96 assert_eq!(common::val_ty(llfn), llptrty);
97 debug!("get_fn: not casting pointer!");
99 if instance.def.is_inline(tcx) {
100 attributes::inline(llfn, attributes::InlineAttr::Hint);
102 attributes::from_fn_attrs(cx, llfn, instance.def.def_id());
104 let instance_def_id = instance.def_id();
106 // Perhaps questionable, but we assume that anything defined
107 // *in Rust code* may unwind. Foreign items like `extern "C" {
108 // fn foo(); }` are assumed not to unwind **unless** they have
109 // a `#[unwind]` attribute.
110 if tcx.sess.panic_strategy() == PanicStrategy::Unwind {
111 if !tcx.is_foreign_item(instance_def_id) {
112 attributes::unwind(llfn, true);
116 // Apply an appropriate linkage/visibility value to our item that we
119 // This is sort of subtle. Inside our codegen unit we started off
120 // compilation by predefining all our own `TransItem` instances. That
121 // is, everything we're translating ourselves is already defined. That
122 // means that anything we're actually translating ourselves will have
123 // hit the above branch in `get_declared_value`. As a result, we're
124 // guaranteed here that we're declaring a symbol that won't get defined,
125 // or in other words we're referencing a foreign value.
127 // So because this is a foreign value we blanket apply an external
128 // linkage directive because it's coming from a different object file.
129 // The visibility here is where it gets tricky. This symbol could be
130 // referencing some foreign crate or foreign library (an `extern`
131 // block) in which case we want to leave the default visibility. We may
132 // also, though, have multiple codegen units.
134 // In the situation of multiple codegen units this function may be
135 // referencing a function from another codegen unit. If we're
136 // indeed referencing a symbol in another codegen unit then we're in one
139 // * This is a symbol defined in a foreign crate and we're just
140 // monomorphizing in another codegen unit. In this case this symbols
141 // is for sure not exported, so both codegen units will be using
142 // hidden visibility. Hence, we apply a hidden visibility here.
144 // * This is a symbol defined in our local crate. If the symbol in the
145 // other codegen unit is also not exported then like with the foreign
146 // case we apply a hidden visibility. If the symbol is exported from
147 // the foreign object file, however, then we leave this at the
148 // default visibility as we'll just import it naturally.
150 llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
152 if cx.tcx.is_translated_item(instance_def_id) {
153 if instance_def_id.is_local() {
154 if !cx.tcx.is_reachable_non_generic(instance_def_id) {
155 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
158 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
163 if cx.use_dll_storage_attrs &&
164 tcx.is_dllimport_foreign_item(instance_def_id)
167 llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
174 cx.instances.borrow_mut().insert(instance, llfn);
179 pub fn resolve_and_get_fn<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
181 substs: &'tcx Substs<'tcx>)
186 ty::Instance::resolve(
188 ty::ParamEnv::empty(traits::Reveal::All),