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|
//! Handles codegen of callees as well as other call-related
//! things. Callees are a superset of normal rust values and sometimes
//! have different representations. In particular, top-level fn items
//! and methods are represented as just a fn ptr and not a full
//! closure.
use crate::abi::FnAbiLlvmExt;
use crate::attributes;
use crate::common;
use crate::context::CodegenCx;
use crate::llvm;
use crate::value::Value;
use rustc_codegen_ssa::traits::*;
use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt};
use rustc_middle::ty::{self, Instance, TypeVisitable};
/// 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<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'tcx>) -> &'ll Value {
let tcx = cx.tcx();
debug!("get_fn(instance={:?})", instance);
assert!(!instance.substs.needs_infer());
assert!(!instance.substs.has_escaping_bound_vars());
if let Some(&llfn) = cx.instances.borrow().get(&instance) {
return llfn;
}
let sym = tcx.symbol_name(instance).name;
debug!(
"get_fn({:?}: {:?}) => {}",
instance,
instance.ty(cx.tcx(), ty::ParamEnv::reveal_all()),
sym
);
let fn_abi = cx.fn_abi_of_instance(instance, ty::List::empty());
let llfn = if let Some(llfn) = cx.get_declared_value(sym) {
// Create a fn pointer with the new signature.
let llptrty = fn_abi.ptr_to_llvm_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(llfn) != llptrty {
debug!("get_fn: casting {:?} to {:?}", llfn, llptrty);
cx.const_ptrcast(llfn, llptrty)
} else {
debug!("get_fn: not casting pointer!");
llfn
}
} else {
let instance_def_id = instance.def_id();
let llfn = if tcx.sess.target.arch == "x86" &&
let Some(dllimport) = common::get_dllimport(tcx, instance_def_id, sym)
{
cx.declare_fn(&common::i686_decorated_name(&dllimport, common::is_mingw_gnu_toolchain(&tcx.sess.target), true), fn_abi)
} else {
cx.declare_fn(sym, fn_abi)
};
debug!("get_fn: not casting pointer!");
attributes::from_fn_attrs(cx, llfn, instance);
// 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).
unsafe {
llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
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()
{
llvm::LLVMRustSetVisibility(llfn, llvm::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() {
llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
}
}
}
} else {
// When not sharing generics, all instances are in the same
// crate and have hidden visibility
llvm::LLVMRustSetVisibility(llfn, llvm::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) {
llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
}
} else {
// This is a function from an upstream crate that has
// been instantiated here. These are always hidden.
llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
}
}
}
// MinGW: For backward compatibility we rely on the linker to decide whether it
// should use dllimport for functions.
if cx.use_dll_storage_attrs
&& tcx.is_dllimport_foreign_item(instance_def_id)
&& !matches!(tcx.sess.target.env.as_ref(), "gnu" | "uclibc")
{
llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
}
if cx.should_assume_dso_local(llfn, true) {
llvm::LLVMRustSetDSOLocal(llfn, true);
}
}
llfn
};
cx.instances.borrow_mut().insert(instance, llfn);
llfn
}
|
