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;
28 use rustc::ty::subst::Substs;
29 use rustc_back::PanicStrategy;
31 /// Translates 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
38 pub fn get_fn<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
39 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);
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 // Perhaps questionable, but we assume that anything defined
106 // *in Rust code* may unwind. Foreign items like `extern "C" {
107 // fn foo(); }` are assumed not to unwind **unless** they have
108 // a `#[unwind]` attribute.
109 if tcx.sess.panic_strategy() == PanicStrategy::Unwind {
110 if !tcx.is_foreign_item(instance_def_id) {
111 attributes::unwind(llfn, true);
115 // Apply an appropriate linkage/visibility value to our item that we
118 // This is sort of subtle. Inside our codegen unit we started off
119 // compilation by predefining all our own `TransItem` instances. That
120 // is, everything we're translating ourselves is already defined. That
121 // means that anything we're actually translating ourselves will have
122 // hit the above branch in `get_declared_value`. As a result, we're
123 // guaranteed here that we're declaring a symbol that won't get defined,
124 // or in other words we're referencing a foreign value.
126 // So because this is a foreign value we blanket apply an external
127 // linkage directive because it's coming from a different object file.
128 // The visibility here is where it gets tricky. This symbol could be
129 // referencing some foreign crate or foreign library (an `extern`
130 // block) in which case we want to leave the default visibility. We may
131 // also, though, have multiple codegen units.
133 // In the situation of multiple codegen units this function may be
134 // referencing a function from another codegen unit. If we're
135 // indeed referencing a symbol in another codegen unit then we're in one
138 // * This is a symbol defined in a foreign crate and we're just
139 // monomorphizing in another codegen unit. In this case this symbols
140 // is for sure not exported, so both codegen units will be using
141 // hidden visibility. Hence, we apply a hidden visibility here.
143 // * This is a symbol defined in our local crate. If the symbol in the
144 // other codegen unit is also not exported then like with the foreign
145 // case we apply a hidden visibility. If the symbol is exported from
146 // the foreign object file, however, then we leave this at the
147 // default visibility as we'll just import it naturally.
149 llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
151 if cx.tcx.is_translated_item(instance_def_id) {
152 if instance_def_id.is_local() {
153 if !cx.tcx.is_reachable_non_generic(instance_def_id) {
154 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
157 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
162 if cx.use_dll_storage_attrs &&
163 tcx.is_dllimport_foreign_item(instance_def_id)
166 llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
173 cx.instances.borrow_mut().insert(instance, llfn);
178 pub fn resolve_and_get_fn<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
180 substs: &'tcx Substs<'tcx>)
185 ty::Instance::resolve(
187 ty::ParamEnv::reveal_all(),