1 //! Handles codegen of callees as well as other call-related
2 //! things. Callees are a superset of normal rust values and sometimes
3 //! have different representations. In particular, top-level fn items
4 //! and methods are represented as just a fn ptr and not a full
7 use crate::abi
::{FnAbi, FnAbiLlvmExt}
;
9 use crate::context
::CodegenCx
;
11 use crate::value
::Value
;
12 use rustc_codegen_ssa
::traits
::*;
15 use rustc_middle
::ty
::layout
::{FnAbiExt, HasTyCtxt}
;
16 use rustc_middle
::ty
::{self, Instance, TypeFoldable}
;
18 /// Codegens a reference to a fn/method item, monomorphizing and
19 /// inlining as it goes.
23 /// - `cx`: the crate context
24 /// - `instance`: the instance to be instantiated
25 pub fn get_fn(cx
: &CodegenCx
<'ll
, 'tcx
>, instance
: Instance
<'tcx
>) -> &'ll Value
{
28 debug
!("get_fn(instance={:?})", instance
);
30 assert
!(!instance
.substs
.needs_infer());
31 assert
!(!instance
.substs
.has_escaping_bound_vars());
33 if let Some(&llfn
) = cx
.instances
.borrow().get(&instance
) {
37 let sym
= tcx
.symbol_name(instance
).name
;
39 "get_fn({:?}: {:?}) => {}",
41 instance
.ty(cx
.tcx(), ty
::ParamEnv
::reveal_all()),
45 let fn_abi
= FnAbi
::of_instance(cx
, instance
, &[]);
47 let llfn
= if let Some(llfn
) = cx
.get_declared_value(&sym
) {
48 // Create a fn pointer with the new signature.
49 let llptrty
= fn_abi
.ptr_to_llvm_type(cx
);
51 // This is subtle and surprising, but sometimes we have to bitcast
52 // the resulting fn pointer. The reason has to do with external
53 // functions. If you have two crates that both bind the same C
54 // library, they may not use precisely the same types: for
55 // example, they will probably each declare their own structs,
56 // which are distinct types from LLVM's point of view (nominal
59 // Now, if those two crates are linked into an application, and
60 // they contain inlined code, you can wind up with a situation
61 // where both of those functions wind up being loaded into this
62 // application simultaneously. In that case, the same function
63 // (from LLVM's point of view) requires two types. But of course
64 // LLVM won't allow one function to have two types.
66 // What we currently do, therefore, is declare the function with
67 // one of the two types (whichever happens to come first) and then
68 // bitcast as needed when the function is referenced to make sure
69 // it has the type we expect.
71 // This can occur on either a crate-local or crate-external
72 // reference. It also occurs when testing libcore and in some
73 // other weird situations. Annoying.
74 if cx
.val_ty(llfn
) != llptrty
{
75 debug
!("get_fn: casting {:?} to {:?}", llfn
, llptrty
);
76 cx
.const_ptrcast(llfn
, llptrty
)
78 debug
!("get_fn: not casting pointer!");
82 let llfn
= cx
.declare_fn(&sym
, &fn_abi
);
83 debug
!("get_fn: not casting pointer!");
85 attributes
::from_fn_attrs(cx
, llfn
, instance
);
87 let instance_def_id
= instance
.def_id();
89 // Apply an appropriate linkage/visibility value to our item that we
92 // This is sort of subtle. Inside our codegen unit we started off
93 // compilation by predefining all our own `MonoItem` instances. That
94 // is, everything we're codegenning ourselves is already defined. That
95 // means that anything we're actually codegenning in this codegen unit
96 // will have hit the above branch in `get_declared_value`. As a result,
97 // we're guaranteed here that we're declaring a symbol that won't get
98 // defined, or in other words we're referencing a value from another
99 // codegen unit or even another crate.
101 // So because this is a foreign value we blanket apply an external
102 // linkage directive because it's coming from a different object file.
103 // The visibility here is where it gets tricky. This symbol could be
104 // referencing some foreign crate or foreign library (an `extern`
105 // block) in which case we want to leave the default visibility. We may
106 // also, though, have multiple codegen units. It could be a
107 // monomorphization, in which case its expected visibility depends on
108 // whether we are sharing generics or not. The important thing here is
109 // that the visibility we apply to the declaration is the same one that
110 // has been applied to the definition (wherever that definition may be).
112 llvm
::LLVMRustSetLinkage(llfn
, llvm
::Linkage
::ExternalLinkage
);
114 let is_generic
= instance
.substs
.non_erasable_generics().next().is_some();
117 // This is a monomorphization. Its expected visibility depends
118 // on whether we are in share-generics mode.
120 if cx
.tcx
.sess
.opts
.share_generics() {
121 // We are in share_generics mode.
123 if let Some(instance_def_id
) = instance_def_id
.as_local() {
124 // This is a definition from the current crate. If the
125 // definition is unreachable for downstream crates or
126 // the current crate does not re-export generics, the
127 // definition of the instance will have been declared
129 if cx
.tcx
.is_unreachable_local_definition(instance_def_id
)
130 || !cx
.tcx
.local_crate_exports_generics()
132 llvm
::LLVMRustSetVisibility(llfn
, llvm
::Visibility
::Hidden
);
135 // This is a monomorphization of a generic function
136 // defined in an upstream crate.
137 if instance
.upstream_monomorphization(tcx
).is_some() {
138 // This is instantiated in another crate. It cannot
141 // This is a local instantiation of an upstream definition.
142 // If the current crate does not re-export it
143 // (because it is a C library or an executable), it
144 // will have been declared `hidden`.
145 if !cx
.tcx
.local_crate_exports_generics() {
146 llvm
::LLVMRustSetVisibility(llfn
, llvm
::Visibility
::Hidden
);
151 // When not sharing generics, all instances are in the same
152 // crate and have hidden visibility
153 llvm
::LLVMRustSetVisibility(llfn
, llvm
::Visibility
::Hidden
);
156 // This is a non-generic function
157 if cx
.tcx
.is_codegened_item(instance_def_id
) {
158 // This is a function that is instantiated in the local crate
160 if instance_def_id
.is_local() {
161 // This is function that is defined in the local crate.
162 // If it is not reachable, it is hidden.
163 if !cx
.tcx
.is_reachable_non_generic(instance_def_id
) {
164 llvm
::LLVMRustSetVisibility(llfn
, llvm
::Visibility
::Hidden
);
167 // This is a function from an upstream crate that has
168 // been instantiated here. These are always hidden.
169 llvm
::LLVMRustSetVisibility(llfn
, llvm
::Visibility
::Hidden
);
175 // MinGW: For backward compatibility we rely on the linker to decide whether it
176 // should use dllimport for functions.
177 if cx
.use_dll_storage_attrs
178 && tcx
.is_dllimport_foreign_item(instance_def_id
)
179 && tcx
.sess
.target
.target
.target_env
!= "gnu"
182 llvm
::LLVMSetDLLStorageClass(llfn
, llvm
::DLLStorageClass
::DllImport
);
189 cx
.instances
.borrow_mut().insert(instance
, llfn
);