rust/src/librustc_trans/callee.rs

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// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Handles translation 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 attributes;
use common::{self, CodegenCx};
use consts;
use declare;
use llvm::{self, ValueRef};
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use monomorphize::Instance;
use type_of::LayoutLlvmExt;
use rustc::hir::def_id::DefId;
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use rustc::ty::{self, TypeFoldable};
use rustc::ty::layout::LayoutOf;
use rustc::ty::subst::Substs;
use rustc_back::PanicStrategy;
/// Translates a reference to a fn/method item, monomorphizing and
/// inlining as it goes.
///
/// # Parameters
///
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/// - `cx`: the crate context
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/// - `instance`: the instance to be instantiated
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pub fn get_fn<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
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instance: Instance<'tcx>)
-> ValueRef
{
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let tcx = cx.tcx;
debug!("get_fn(instance={:?})", instance);
assert!(!instance.substs.needs_infer());
assert!(!instance.substs.has_escaping_regions());
assert!(!instance.substs.has_param_types());
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let fn_ty = instance.ty(cx.tcx);
if let Some(&llfn) = cx.instances.borrow().get(&instance) {
return llfn;
}
let sym = tcx.symbol_name(instance);
debug!("get_fn({:?}: {:?}) => {}", instance, fn_ty, sym);
// Create a fn pointer with the substituted signature.
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let fn_ptr_ty = tcx.mk_fn_ptr(common::ty_fn_sig(cx, fn_ty));
let llptrty = cx.layout_of(fn_ptr_ty).llvm_type(cx);
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let llfn = if let Some(llfn) = declare::get_declared_value(cx, &sym) {
// 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 common::val_ty(llfn) != llptrty {
debug!("get_fn: casting {:?} to {:?}", llfn, llptrty);
consts::ptrcast(llfn, llptrty)
} else {
debug!("get_fn: not casting pointer!");
llfn
}
} else {
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let llfn = declare::declare_fn(cx, &sym, fn_ty);
assert_eq!(common::val_ty(llfn), llptrty);
debug!("get_fn: not casting pointer!");
if instance.def.is_inline(tcx) {
attributes::inline(llfn, attributes::InlineAttr::Hint);
}
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attributes::from_fn_attrs(cx, llfn, instance.def.def_id());
let instance_def_id = instance.def_id();
// Perhaps questionable, but we assume that anything defined
// *in Rust code* may unwind. Foreign items like `extern "C" {
// fn foo(); }` are assumed not to unwind **unless** they have
// a `#[unwind]` attribute.
if tcx.sess.panic_strategy() == PanicStrategy::Unwind {
if !tcx.is_foreign_item(instance_def_id) {
attributes::unwind(llfn, true);
}
}
// 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 `TransItem` instances. That
// is, everything we're translating ourselves is already defined. That
// means that anything we're actually translating ourselves 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 foreign value.
//
// 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.
//
// In the situation of multiple codegen units this function may be
// referencing a function from another codegen unit. If we're
// indeed referencing a symbol in another codegen unit then we're in one
// of two cases:
//
// * This is a symbol defined in a foreign crate and we're just
// monomorphizing in another codegen unit. In this case this symbols
// is for sure not exported, so both codegen units will be using
// hidden visibility. Hence, we apply a hidden visibility here.
//
// * This is a symbol defined in our local crate. If the symbol in the
// other codegen unit is also not exported then like with the foreign
// case we apply a hidden visibility. If the symbol is exported from
// the foreign object file, however, then we leave this at the
// default visibility as we'll just import it naturally.
unsafe {
llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
if cx.tcx.is_translated_item(instance_def_id) {
if instance_def_id.is_local() {
if !cx.tcx.is_reachable_non_generic(instance_def_id) {
llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
}
} else {
llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
}
}
}
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if cx.use_dll_storage_attrs &&
tcx.is_dllimport_foreign_item(instance_def_id)
{
unsafe {
llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
}
}
llfn
};
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cx.instances.borrow_mut().insert(instance, llfn);
llfn
}
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pub fn resolve_and_get_fn<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
def_id: DefId,
substs: &'tcx Substs<'tcx>)
-> ValueRef
{
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get_fn(
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cx,
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ty::Instance::resolve(
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cx.tcx,
ty::ParamEnv::reveal_all(),
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def_id,
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substs
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).unwrap()
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)
}