rust/src/librustc/middle/intrinsicck.rs

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// Copyright 2012-2014 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.
use dep_graph::DepNode;
use middle::def::Def;
use middle::def_id::DefId;
use middle::subst::{Subst, Substs, EnumeratedItems};
use middle::ty::{TransmuteRestriction, TyCtxt};
use middle::ty::{self, Ty, TypeFoldable};
use std::fmt;
use syntax::abi::Abi::RustIntrinsic;
use syntax::ast;
use syntax::codemap::Span;
use rustc_front::intravisit::{self, Visitor, FnKind};
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use rustc_front::hir;
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pub fn check_crate(tcx: &TyCtxt) {
let mut visitor = IntrinsicCheckingVisitor {
tcx: tcx,
param_envs: Vec::new(),
dummy_sized_ty: tcx.types.isize,
dummy_unsized_ty: tcx.mk_slice(tcx.types.isize),
};
tcx.visit_all_items_in_krate(DepNode::IntrinsicCheck, &mut visitor);
}
struct IntrinsicCheckingVisitor<'a, 'tcx: 'a> {
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tcx: &'a TyCtxt<'tcx>,
// As we traverse the AST, we keep a stack of the parameter
// environments for each function we encounter. When we find a
// call to `transmute`, we can check it in the context of the top
// of the stack (which ought not to be empty).
param_envs: Vec<ty::ParameterEnvironment<'a,'tcx>>,
// Dummy sized/unsized types that use to substitute for type
// parameters in order to estimate how big a type will be for any
// possible instantiation of the type parameters in scope. See
// `check_transmute` for more details.
dummy_sized_ty: Ty<'tcx>,
dummy_unsized_ty: Ty<'tcx>,
}
impl<'a, 'tcx> IntrinsicCheckingVisitor<'a, 'tcx> {
fn def_id_is_transmute(&self, def_id: DefId) -> bool {
let intrinsic = match self.tcx.lookup_item_type(def_id).ty.sty {
ty::TyFnDef(_, _, ref bfty) => bfty.abi == RustIntrinsic,
_ => return false
};
intrinsic && self.tcx.item_name(def_id).as_str() == "transmute"
}
fn check_transmute(&self, span: Span, from: Ty<'tcx>, to: Ty<'tcx>, id: ast::NodeId) {
// Find the parameter environment for the most recent function that
// we entered.
let param_env = match self.param_envs.last() {
Some(p) => p,
None => {
self.tcx.sess.span_bug(
span,
"transmute encountered outside of any fn");
}
};
// Simple case: no type parameters involved.
if
!from.has_param_types() && !from.has_self_ty() &&
!to.has_param_types() && !to.has_self_ty()
{
let restriction = TransmuteRestriction {
span: span,
original_from: from,
original_to: to,
substituted_from: from,
substituted_to: to,
id: id,
};
self.push_transmute_restriction(restriction);
return;
}
// The rules around type parameters are a bit subtle. We are
// checking these rules before monomorphization, so there may
// be unsubstituted type parameters present in the
// types. Obviously we cannot create LLVM types for those.
// However, if a type parameter appears only indirectly (i.e.,
// through a pointer), it does not necessarily affect the
// size, so that should be allowed. The only catch is that we
// DO want to be careful around unsized type parameters, since
// fat pointers have a different size than a thin pointer, and
// hence `&T` and `&U` have different sizes if `T : Sized` but
// `U : Sized` does not hold.
//
// However, it's not as simple as checking whether `T :
// Sized`, because even if `T : Sized` does not hold, that
// just means that `T` *may* not be sized. After all, even a
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// type parameter `T: ?Sized` could be bound to a sized
// type. (Issue #20116)
//
// To handle this, we first check for "interior" type
// parameters, which are always illegal. If there are none of
// those, then we know that the only way that all type
// parameters `T` are referenced indirectly, e.g. via a
// pointer type like `&T`. In that case, we only care whether
// `T` is sized or not, because that influences whether `&T`
// is a thin or fat pointer.
//
// One could imagine establishing a sophisticated constraint
// system to ensure that the transmute is legal, but instead
// we do something brutally dumb. We just substitute dummy
// sized or unsized types for every type parameter in scope,
// exhaustively checking all possible combinations. Here are some examples:
//
// ```
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// fn foo<T, U>() {
// // T=int, U=int
// }
//
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// fn bar<T: ?Sized, U>() {
// // T=int, U=int
// // T=[int], U=int
// }
//
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// fn baz<T: ?Sized, U: ?Sized>() {
// // T=int, U=int
// // T=[int], U=int
// // T=int, U=[int]
// // T=[int], U=[int]
// }
// ```
//
// In all cases, we keep the original unsubstituted types
// around for error reporting.
let from_tc = from.type_contents(self.tcx);
let to_tc = to.type_contents(self.tcx);
if from_tc.interior_param() || to_tc.interior_param() {
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span_err!(self.tcx.sess, span, E0139,
"cannot transmute to or from a type that contains \
unsubstituted type parameters");
return;
}
let mut substs = param_env.free_substs.clone();
self.with_each_combination(
span,
param_env,
param_env.free_substs.types.iter_enumerated(),
&mut substs,
&mut |substs| {
let restriction = TransmuteRestriction {
span: span,
original_from: from,
original_to: to,
substituted_from: from.subst(self.tcx, substs),
substituted_to: to.subst(self.tcx, substs),
id: id,
};
self.push_transmute_restriction(restriction);
});
}
fn with_each_combination(&self,
span: Span,
param_env: &ty::ParameterEnvironment<'a,'tcx>,
mut types_in_scope: EnumeratedItems<Ty<'tcx>>,
substs: &mut Substs<'tcx>,
callback: &mut FnMut(&Substs<'tcx>))
{
// This parameter invokes `callback` many times with different
// substitutions that replace all the parameters in scope with
// either `int` or `[int]`, depending on whether the type
// parameter is known to be sized. See big comment above for
// an explanation of why this is a reasonable thing to do.
match types_in_scope.next() {
None => {
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debug!("with_each_combination(substs={:?})",
substs);
callback(substs);
}
Some((space, index, &param_ty)) => {
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debug!("with_each_combination: space={:?}, index={}, param_ty={:?}",
space, index, param_ty);
if !param_ty.is_sized(param_env, span) {
debug!("with_each_combination: param_ty is not known to be sized");
substs.types.get_mut_slice(space)[index] = self.dummy_unsized_ty;
self.with_each_combination(span, param_env, types_in_scope.clone(),
substs, callback);
}
substs.types.get_mut_slice(space)[index] = self.dummy_sized_ty;
self.with_each_combination(span, param_env, types_in_scope,
substs, callback);
}
}
}
fn push_transmute_restriction(&self, restriction: TransmuteRestriction<'tcx>) {
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debug!("Pushing transmute restriction: {:?}", restriction);
self.tcx.transmute_restrictions.borrow_mut().push(restriction);
}
}
impl<'a, 'tcx, 'v> Visitor<'v> for IntrinsicCheckingVisitor<'a, 'tcx> {
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fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v hir::FnDecl,
b: &'v hir::Block, s: Span, id: ast::NodeId) {
match fk {
FnKind::ItemFn(..) | FnKind::Method(..) => {
let param_env = ty::ParameterEnvironment::for_item(self.tcx, id);
self.param_envs.push(param_env);
intravisit::walk_fn(self, fk, fd, b, s);
self.param_envs.pop();
}
FnKind::Closure(..) => {
intravisit::walk_fn(self, fk, fd, b, s);
}
}
}
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fn visit_expr(&mut self, expr: &hir::Expr) {
if let hir::ExprPath(..) = expr.node {
match self.tcx.resolve_expr(expr) {
Def::Fn(did) if self.def_id_is_transmute(did) => {
let typ = self.tcx.node_id_to_type(expr.id);
match typ.sty {
ty::TyFnDef(_, _, ref bare_fn_ty) if bare_fn_ty.abi == RustIntrinsic => {
if let ty::FnConverging(to) = bare_fn_ty.sig.0.output {
let from = bare_fn_ty.sig.0.inputs[0];
self.check_transmute(expr.span, from, to, expr.id);
}
}
_ => {
self.tcx
.sess
.span_bug(expr.span, "transmute wasn't a bare fn?!");
}
}
}
_ => {}
}
}
intravisit::walk_expr(self, expr);
}
}
impl<'tcx> fmt::Debug for TransmuteRestriction<'tcx> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "TransmuteRestriction(id={}, original=({:?},{:?}), substituted=({:?},{:?}))",
self.id,
self.original_from,
self.original_to,
self.substituted_from,
self.substituted_to)
}
}