src/librustc_trans/consts.rs

   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.
   4 //
   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.
  10
  11
  12 use llvm;
  13 use llvm::{ConstFCmp, ConstICmp, SetLinkage, SetUnnamedAddr};
  14 use llvm::{InternalLinkage, ValueRef, Bool, True};
  15 use middle::const_qualif::ConstQualif;
  16 use rustc_const_eval::{ConstEvalErr, lookup_const_fn_by_id, lookup_const_by_id, ErrKind};
  17 use rustc_const_eval::eval_repeat_count;
  18 use rustc::hir::def::Def;
  19 use rustc::hir::def_id::DefId;
  20 use rustc::hir::map as hir_map;
  21 use {abi, adt, closure, debuginfo, expr, machine};
  22 use base::{self, exported_name, imported_name, push_ctxt};
  23 use callee::Callee;
  24 use collector::{self, TransItem};
  25 use common::{type_is_sized, C_nil, const_get_elt};
  26 use common::{CrateContext, C_integral, C_floating, C_bool, C_str_slice, C_bytes, val_ty};
  27 use common::{C_struct, C_undef, const_to_opt_int, const_to_opt_uint, VariantInfo, C_uint};
  28 use common::{type_is_fat_ptr, Field, C_vector, C_array, C_null};
  29 use datum::{Datum, Lvalue};
  30 use declare;
  31 use monomorphize::{self, Instance};
  32 use type_::Type;
  33 use type_of;
  34 use value::Value;
  35 use Disr;
  36 use rustc::ty::subst::Substs;
  37 use rustc::ty::adjustment::{AdjustDerefRef, AdjustReifyFnPointer};
  38 use rustc::ty::adjustment::{AdjustUnsafeFnPointer, AdjustMutToConstPointer};
  39 use rustc::ty::{self, Ty, TyCtxt};
  40 use rustc::ty::cast::{CastTy,IntTy};
  41 use util::nodemap::NodeMap;
  42 use rustc_const_math::{ConstInt, ConstMathErr, ConstUsize, ConstIsize};
  43
  44 use rustc::hir;
  45
  46 use std::ffi::{CStr, CString};
  47 use std::borrow::Cow;
  48 use libc::c_uint;
  49 use syntax::ast::{self, LitKind};
  50 use syntax::attr::{self, AttrMetaMethods};
  51 use syntax::parse::token;
  52 use syntax::ptr::P;
  53
  54 pub type FnArgMap<'a> = Option<&'a NodeMap<ValueRef>>;
  55
  56 pub fn const_lit(cx: &CrateContext, e: &hir::Expr, lit: &ast::Lit)
  57     -> ValueRef {
  58     let _icx = push_ctxt("trans_lit");
  59     debug!("const_lit: {:?}", lit);
  60     match lit.node {
  61         LitKind::Byte(b) => C_integral(Type::uint_from_ty(cx, ast::UintTy::U8), b as u64, false),
  62         LitKind::Char(i) => C_integral(Type::char(cx), i as u64, false),
  63         LitKind::Int(i, ast::LitIntType::Signed(t)) => {
  64             C_integral(Type::int_from_ty(cx, t), i, true)
  65         }
  66         LitKind::Int(u, ast::LitIntType::Unsigned(t)) => {
  67             C_integral(Type::uint_from_ty(cx, t), u, false)
  68         }
  69         LitKind::Int(i, ast::LitIntType::Unsuffixed) => {
  70             let lit_int_ty = cx.tcx().node_id_to_type(e.id);
  71             match lit_int_ty.sty {
  72                 ty::TyInt(t) => {
  73                     C_integral(Type::int_from_ty(cx, t), i as u64, true)
  74                 }
  75                 ty::TyUint(t) => {
  76                     C_integral(Type::uint_from_ty(cx, t), i as u64, false)
  77                 }
  78                 _ => span_bug!(lit.span,
  79                         "integer literal has type {:?} (expected int \
  80                          or usize)",
  81                         lit_int_ty)
  82             }
  83         }
  84         LitKind::Float(ref fs, t) => {
  85             C_floating(&fs, Type::float_from_ty(cx, t))
  86         }
  87         LitKind::FloatUnsuffixed(ref fs) => {
  88             let lit_float_ty = cx.tcx().node_id_to_type(e.id);
  89             match lit_float_ty.sty {
  90                 ty::TyFloat(t) => {
  91                     C_floating(&fs, Type::float_from_ty(cx, t))
  92                 }
  93                 _ => {
  94                     span_bug!(lit.span,
  95                         "floating point literal doesn't have the right type");
  96                 }
  97             }
  98         }
  99         LitKind::Bool(b) => C_bool(cx, b),
 100         LitKind::Str(ref s, _) => C_str_slice(cx, (*s).clone()),
 101         LitKind::ByteStr(ref data) => {
 102             addr_of(cx, C_bytes(cx, &data[..]), 1, "byte_str")
 103         }
 104     }
 105 }
 106
 107 pub fn ptrcast(val: ValueRef, ty: Type) -> ValueRef {
 108     unsafe {
 109         llvm::LLVMConstPointerCast(val, ty.to_ref())
 110     }
 111 }
 112
 113 fn addr_of_mut(ccx: &CrateContext,
 114                cv: ValueRef,
 115                align: machine::llalign,
 116                kind: &str)
 117                -> ValueRef {
 118     unsafe {
 119         // FIXME: this totally needs a better name generation scheme, perhaps a simple global
 120         // counter? Also most other uses of gensym in trans.
 121         let gsym = token::gensym("_");
 122         let name = format!("{}{}", kind, gsym.0);
 123         let gv = declare::define_global(ccx, &name[..], val_ty(cv)).unwrap_or_else(||{
 124             bug!("symbol `{}` is already defined", name);
 125         });
 126         llvm::LLVMSetInitializer(gv, cv);
 127         llvm::LLVMSetAlignment(gv, align);
 128         SetLinkage(gv, InternalLinkage);
 129         SetUnnamedAddr(gv, true);
 130         gv
 131     }
 132 }
 133
 134 pub fn addr_of(ccx: &CrateContext,
 135                cv: ValueRef,
 136                align: machine::llalign,
 137                kind: &str)
 138                -> ValueRef {
 139     match ccx.const_globals().borrow().get(&cv) {
 140         Some(&gv) => {
 141             unsafe {
 142                 // Upgrade the alignment in cases where the same constant is used with different
 143                 // alignment requirements
 144                 if align > llvm::LLVMGetAlignment(gv) {
 145                     llvm::LLVMSetAlignment(gv, align);
 146                 }
 147             }
 148             return gv;
 149         }
 150         None => {}
 151     }
 152     let gv = addr_of_mut(ccx, cv, align, kind);
 153     unsafe {
 154         llvm::LLVMSetGlobalConstant(gv, True);
 155     }
 156     ccx.const_globals().borrow_mut().insert(cv, gv);
 157     gv
 158 }
 159
 160 /// Deref a constant pointer
 161 fn load_const(cx: &CrateContext, v: ValueRef, t: Ty) -> ValueRef {
 162     let v = match cx.const_unsized().borrow().get(&v) {
 163         Some(&v) => v,
 164         None => v
 165     };
 166     let d = unsafe { llvm::LLVMGetInitializer(v) };
 167     if t.is_bool() {
 168         unsafe { llvm::LLVMConstTrunc(d, Type::i1(cx).to_ref()) }
 169     } else {
 170         d
 171     }
 172 }
 173
 174 fn const_deref<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
 175                          v: ValueRef,
 176                          ty: Ty<'tcx>)
 177                          -> (ValueRef, Ty<'tcx>) {
 178     match ty.builtin_deref(true, ty::NoPreference) {
 179         Some(mt) => {
 180             if type_is_sized(cx.tcx(), mt.ty) {
 181                 (load_const(cx, v, mt.ty), mt.ty)
 182             } else {
 183                 // Derefing a fat pointer does not change the representation,
 184                 // just the type to the unsized contents.
 185                 (v, mt.ty)
 186             }
 187         }
 188         None => {
 189             bug!("unexpected dereferenceable type {:?}", ty)
 190         }
 191     }
 192 }
 193
 194 fn const_fn_call<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 195                            def_id: DefId,
 196                            substs: Substs<'tcx>,
 197                            arg_vals: &[ValueRef],
 198                            param_substs: &'tcx Substs<'tcx>,
 199                            trueconst: TrueConst) -> Result<ValueRef, ConstEvalFailure> {
 200     let fn_like = lookup_const_fn_by_id(ccx.tcx(), def_id);
 201     let fn_like = fn_like.expect("lookup_const_fn_by_id failed in const_fn_call");
 202
 203     let body = match fn_like.body().expr {
 204         Some(ref expr) => expr,
 205         None => return Ok(C_nil(ccx))
 206     };
 207
 208     let args = &fn_like.decl().inputs;
 209     assert_eq!(args.len(), arg_vals.len());
 210
 211     let arg_ids = args.iter().map(|arg| arg.pat.id);
 212     let fn_args = arg_ids.zip(arg_vals.iter().cloned()).collect();
 213
 214     let substs = monomorphize::apply_param_substs(ccx.tcx(),
 215                                                   param_substs,
 216                                                   &substs.erase_regions());
 217     let substs = ccx.tcx().mk_substs(substs);
 218
 219     const_expr(ccx, body, substs, Some(&fn_args), trueconst).map(|(res, _)| res)
 220 }
 221
 222 pub fn get_const_expr<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 223                                 def_id: DefId,
 224                                 ref_expr: &hir::Expr,
 225                                 param_substs: &'tcx Substs<'tcx>)
 226                                 -> &'tcx hir::Expr {
 227     let substs = ccx.tcx().node_id_item_substs(ref_expr.id).substs;
 228     let substs = monomorphize::apply_param_substs(ccx.tcx(),
 229                                                   param_substs,
 230                                                   &substs.erase_regions());
 231     match lookup_const_by_id(ccx.tcx(), def_id, Some(substs)) {
 232         Some((ref expr, _ty)) => expr,
 233         None => {
 234             span_bug!(ref_expr.span, "constant item not found")
 235         }
 236     }
 237 }
 238
 239 pub enum ConstEvalFailure {
 240     /// in case the const evaluator failed on something that panic at runtime
 241     /// as defined in RFC 1229
 242     Runtime(ConstEvalErr),
 243     // in case we found a true constant
 244     Compiletime(ConstEvalErr),
 245 }
 246
 247 impl ConstEvalFailure {
 248     fn into_inner(self) -> ConstEvalErr {
 249         match self {
 250             Runtime(e) => e,
 251             Compiletime(e) => e,
 252         }
 253     }
 254     pub fn description(&self) -> Cow<str> {
 255         match self {
 256             &Runtime(ref e) => e.description(),
 257             &Compiletime(ref e) => e.description(),
 258         }
 259     }
 260 }
 261
 262 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 263 pub enum TrueConst {
 264     Yes, No
 265 }
 266
 267 use self::ConstEvalFailure::*;
 268
 269 fn get_const_val<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 270                            def_id: DefId,
 271                            ref_expr: &hir::Expr,
 272                            param_substs: &'tcx Substs<'tcx>)
 273                            -> Result<ValueRef, ConstEvalFailure> {
 274     let expr = get_const_expr(ccx, def_id, ref_expr, param_substs);
 275     let empty_substs = ccx.tcx().mk_substs(Substs::empty());
 276     match get_const_expr_as_global(ccx, expr, ConstQualif::empty(), empty_substs, TrueConst::Yes) {
 277         Err(Runtime(err)) => {
 278             ccx.tcx().sess.span_err(expr.span, &err.description());
 279             Err(Compiletime(err))
 280         },
 281         other => other,
 282     }
 283 }
 284
 285 pub fn get_const_expr_as_global<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 286                                           expr: &hir::Expr,
 287                                           qualif: ConstQualif,
 288                                           param_substs: &'tcx Substs<'tcx>,
 289                                           trueconst: TrueConst)
 290                                           -> Result<ValueRef, ConstEvalFailure> {
 291     debug!("get_const_expr_as_global: {:?}", expr.id);
 292     // Special-case constants to cache a common global for all uses.
 293     if let hir::ExprPath(..) = expr.node {
 294         // `def` must be its own statement and cannot be in the `match`
 295         // otherwise the `def_map` will be borrowed for the entire match instead
 296         // of just to get the `def` value
 297         let def = ccx.tcx().def_map.borrow().get(&expr.id).unwrap().full_def();
 298         match def {
 299             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 300                 if !ccx.tcx().tables.borrow().adjustments.contains_key(&expr.id) {
 301                     debug!("get_const_expr_as_global ({:?}): found const {:?}",
 302                            expr.id, def_id);
 303                     return get_const_val(ccx, def_id, expr, param_substs);
 304                 }
 305             },
 306             _ => {},
 307         }
 308     }
 309
 310     let key = (expr.id, param_substs);
 311     if let Some(&val) = ccx.const_values().borrow().get(&key) {
 312         return Ok(val);
 313     }
 314     let ty = monomorphize::apply_param_substs(ccx.tcx(), param_substs,
 315                                               &ccx.tcx().expr_ty(expr));
 316     let val = if qualif.intersects(ConstQualif::NON_STATIC_BORROWS) {
 317         // Avoid autorefs as they would create global instead of stack
 318         // references, even when only the latter are correct.
 319         const_expr_unadjusted(ccx, expr, ty, param_substs, None, trueconst)?
 320     } else {
 321         const_expr(ccx, expr, param_substs, None, trueconst)?.0
 322     };
 323
 324     // boolean SSA values are i1, but they have to be stored in i8 slots,
 325     // otherwise some LLVM optimization passes don't work as expected
 326     let val = unsafe {
 327         if llvm::LLVMTypeOf(val) == Type::i1(ccx).to_ref() {
 328             llvm::LLVMConstZExt(val, Type::i8(ccx).to_ref())
 329         } else {
 330             val
 331         }
 332     };
 333
 334     let lvalue = addr_of(ccx, val, type_of::align_of(ccx, ty), "const");
 335     ccx.const_values().borrow_mut().insert(key, lvalue);
 336     Ok(lvalue)
 337 }
 338
 339 pub fn const_expr<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
 340                             e: &hir::Expr,
 341                             param_substs: &'tcx Substs<'tcx>,
 342                             fn_args: FnArgMap,
 343                             trueconst: TrueConst)
 344                             -> Result<(ValueRef, Ty<'tcx>), ConstEvalFailure> {
 345     let ety = monomorphize::apply_param_substs(cx.tcx(), param_substs,
 346                                                &cx.tcx().expr_ty(e));
 347     let llconst = const_expr_unadjusted(cx, e, ety, param_substs, fn_args, trueconst)?;
 348     let mut llconst = llconst;
 349     let mut ety_adjusted = monomorphize::apply_param_substs(cx.tcx(), param_substs,
 350                                                             &cx.tcx().expr_ty_adjusted(e));
 351     let opt_adj = cx.tcx().tables.borrow().adjustments.get(&e.id).cloned();
 352     match opt_adj {
 353         Some(AdjustReifyFnPointer) => {
 354             match ety.sty {
 355                 ty::TyFnDef(def_id, substs, _) => {
 356                     llconst = Callee::def(cx, def_id, substs).reify(cx).val;
 357                 }
 358                 _ => {
 359                     bug!("{} cannot be reified to a fn ptr", ety)
 360                 }
 361             }
 362         }
 363         Some(AdjustUnsafeFnPointer) | Some(AdjustMutToConstPointer) => {
 364             // purely a type-level thing
 365         }
 366         Some(AdjustDerefRef(adj)) => {
 367             let mut ty = ety;
 368             // Save the last autoderef in case we can avoid it.
 369             if adj.autoderefs > 0 {
 370                 for _ in 0..adj.autoderefs-1 {
 371                     let (dv, dt) = const_deref(cx, llconst, ty);
 372                     llconst = dv;
 373                     ty = dt;
 374                 }
 375             }
 376
 377             if adj.autoref.is_some() {
 378                 if adj.autoderefs == 0 {
 379                     // Don't copy data to do a deref+ref
 380                     // (i.e., skip the last auto-deref).
 381                     llconst = addr_of(cx, llconst, type_of::align_of(cx, ty), "autoref");
 382                     ty = cx.tcx().mk_imm_ref(cx.tcx().mk_region(ty::ReStatic), ty);
 383                 }
 384             } else if adj.autoderefs > 0 {
 385                 let (dv, dt) = const_deref(cx, llconst, ty);
 386                 llconst = dv;
 387
 388                 // If we derefed a fat pointer then we will have an
 389                 // open type here. So we need to update the type with
 390                 // the one returned from const_deref.
 391                 ety_adjusted = dt;
 392             }
 393
 394             if let Some(target) = adj.unsize {
 395                 let target = monomorphize::apply_param_substs(cx.tcx(),
 396                                                               param_substs,
 397                                                               &target);
 398
 399                 let pointee_ty = ty.builtin_deref(true, ty::NoPreference)
 400                     .expect("consts: unsizing got non-pointer type").ty;
 401                 let (base, old_info) = if !type_is_sized(cx.tcx(), pointee_ty) {
 402                     // Normally, the source is a thin pointer and we are
 403                     // adding extra info to make a fat pointer. The exception
 404                     // is when we are upcasting an existing object fat pointer
 405                     // to use a different vtable. In that case, we want to
 406                     // load out the original data pointer so we can repackage
 407                     // it.
 408                     (const_get_elt(llconst, &[abi::FAT_PTR_ADDR as u32]),
 409                      Some(const_get_elt(llconst, &[abi::FAT_PTR_EXTRA as u32])))
 410                 } else {
 411                     (llconst, None)
 412                 };
 413
 414                 let unsized_ty = target.builtin_deref(true, ty::NoPreference)
 415                     .expect("consts: unsizing got non-pointer target type").ty;
 416                 let ptr_ty = type_of::in_memory_type_of(cx, unsized_ty).ptr_to();
 417                 let base = ptrcast(base, ptr_ty);
 418                 let info = base::unsized_info(cx, pointee_ty, unsized_ty, old_info);
 419
 420                 if old_info.is_none() {
 421                     let prev_const = cx.const_unsized().borrow_mut()
 422                                        .insert(base, llconst);
 423                     assert!(prev_const.is_none() || prev_const == Some(llconst));
 424                 }
 425                 assert_eq!(abi::FAT_PTR_ADDR, 0);
 426                 assert_eq!(abi::FAT_PTR_EXTRA, 1);
 427                 llconst = C_struct(cx, &[base, info], false);
 428             }
 429         }
 430         None => {}
 431     };
 432
 433     let llty = type_of::sizing_type_of(cx, ety_adjusted);
 434     let csize = machine::llsize_of_alloc(cx, val_ty(llconst));
 435     let tsize = machine::llsize_of_alloc(cx, llty);
 436     if csize != tsize {
 437         cx.sess().abort_if_errors();
 438         unsafe {
 439             // FIXME these values could use some context
 440             llvm::LLVMDumpValue(llconst);
 441             llvm::LLVMDumpValue(C_undef(llty));
 442         }
 443         bug!("const {:?} of type {:?} has size {} instead of {}",
 444              e, ety_adjusted,
 445              csize, tsize);
 446     }
 447     Ok((llconst, ety_adjusted))
 448 }
 449
 450 fn check_unary_expr_validity(cx: &CrateContext, e: &hir::Expr, t: Ty,
 451                              te: ValueRef, trueconst: TrueConst) -> Result<(), ConstEvalFailure> {
 452     // The only kind of unary expression that we check for validity
 453     // here is `-expr`, to check if it "overflows" (e.g. `-i32::MIN`).
 454     if let hir::ExprUnary(hir::UnNeg, ref inner_e) = e.node {
 455
 456         // An unfortunate special case: we parse e.g. -128 as a
 457         // negation of the literal 128, which means if we're expecting
 458         // a i8 (or if it was already suffixed, e.g. `-128_i8`), then
 459         // 128 will have already overflowed to -128, and so then the
 460         // constant evaluator thinks we're trying to negate -128.
 461         //
 462         // Catch this up front by looking for ExprLit directly,
 463         // and just accepting it.
 464         if let hir::ExprLit(_) = inner_e.node { return Ok(()); }
 465         let cval = match to_const_int(te, t, cx.tcx()) {
 466             Some(v) => v,
 467             None => return Ok(()),
 468         };
 469         match -cval {
 470             Ok(_) => return Ok(()),
 471             Err(err) => const_err(cx, e, Err(err), trueconst),
 472         }
 473     } else {
 474         Ok(())
 475     }
 476 }
 477
 478 fn to_const_int(value: ValueRef, t: Ty, tcx: &TyCtxt) -> Option<ConstInt> {
 479     match t.sty {
 480         ty::TyInt(int_type) => const_to_opt_int(value).and_then(|input| match int_type {
 481             ast::IntTy::I8 => {
 482                 assert_eq!(input as i8 as i64, input);
 483                 Some(ConstInt::I8(input as i8))
 484             },
 485             ast::IntTy::I16 => {
 486                 assert_eq!(input as i16 as i64, input);
 487                 Some(ConstInt::I16(input as i16))
 488             },
 489             ast::IntTy::I32 => {
 490                 assert_eq!(input as i32 as i64, input);
 491                 Some(ConstInt::I32(input as i32))
 492             },
 493             ast::IntTy::I64 => {
 494                 Some(ConstInt::I64(input))
 495             },
 496             ast::IntTy::Is => {
 497                 ConstIsize::new(input, tcx.sess.target.int_type)
 498                     .ok().map(ConstInt::Isize)
 499             },
 500         }),
 501         ty::TyUint(uint_type) => const_to_opt_uint(value).and_then(|input| match uint_type {
 502             ast::UintTy::U8 => {
 503                 assert_eq!(input as u8 as u64, input);
 504                 Some(ConstInt::U8(input as u8))
 505             },
 506             ast::UintTy::U16 => {
 507                 assert_eq!(input as u16 as u64, input);
 508                 Some(ConstInt::U16(input as u16))
 509             },
 510             ast::UintTy::U32 => {
 511                 assert_eq!(input as u32 as u64, input);
 512                 Some(ConstInt::U32(input as u32))
 513             },
 514             ast::UintTy::U64 => {
 515                 Some(ConstInt::U64(input))
 516             },
 517             ast::UintTy::Us => {
 518                 ConstUsize::new(input, tcx.sess.target.uint_type)
 519                     .ok().map(ConstInt::Usize)
 520             },
 521         }),
 522         _ => None,
 523     }
 524 }
 525
 526 fn const_err(cx: &CrateContext,
 527              e: &hir::Expr,
 528              result: Result<ConstInt, ConstMathErr>,
 529              trueconst: TrueConst)
 530              -> Result<(), ConstEvalFailure> {
 531     match (result, trueconst) {
 532         (Ok(_), _) => {
 533             // We do not actually care about a successful result.
 534             Ok(())
 535         },
 536         (Err(err), TrueConst::Yes) => {
 537             let err = ConstEvalErr{ span: e.span, kind: ErrKind::Math(err) };
 538             cx.tcx().sess.span_err(e.span, &err.description());
 539             Err(Compiletime(err))
 540         },
 541         (Err(err), TrueConst::No) => {
 542             let err = ConstEvalErr{ span: e.span, kind: ErrKind::Math(err) };
 543             cx.tcx().sess.span_warn(e.span, &err.description());
 544             Err(Runtime(err))
 545         },
 546     }
 547 }
 548
 549 fn check_binary_expr_validity(cx: &CrateContext, e: &hir::Expr, t: Ty,
 550                               te1: ValueRef, te2: ValueRef,
 551                               trueconst: TrueConst) -> Result<(), ConstEvalFailure> {
 552     let b = if let hir::ExprBinary(b, _, _) = e.node { b } else { bug!() };
 553     let (lhs, rhs) = match (to_const_int(te1, t, cx.tcx()), to_const_int(te2, t, cx.tcx())) {
 554         (Some(v1), Some(v2)) => (v1, v2),
 555         _ => return Ok(()),
 556     };
 557     let result = match b.node {
 558         hir::BiAdd => lhs + rhs,
 559         hir::BiSub => lhs - rhs,
 560         hir::BiMul => lhs * rhs,
 561         hir::BiDiv => lhs / rhs,
 562         hir::BiRem => lhs % rhs,
 563         hir::BiShl => lhs << rhs,
 564         hir::BiShr => lhs >> rhs,
 565         _ => return Ok(()),
 566     };
 567     const_err(cx, e, result, trueconst)
 568 }
 569
 570 fn const_expr_unadjusted<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
 571                                    e: &hir::Expr,
 572                                    ety: Ty<'tcx>,
 573                                    param_substs: &'tcx Substs<'tcx>,
 574                                    fn_args: FnArgMap,
 575                                    trueconst: TrueConst)
 576                                    -> Result<ValueRef, ConstEvalFailure>
 577 {
 578     debug!("const_expr_unadjusted(e={:?}, ety={:?}, param_substs={:?})",
 579            e,
 580            ety,
 581            param_substs);
 582
 583     let map_list = |exprs: &[P<hir::Expr>]| -> Result<Vec<ValueRef>, ConstEvalFailure> {
 584         exprs.iter()
 585              .map(|e| const_expr(cx, &e, param_substs, fn_args, trueconst).map(|(l, _)| l))
 586              .collect::<Vec<Result<ValueRef, ConstEvalFailure>>>()
 587              .into_iter()
 588              .collect()
 589          // this dance is necessary to eagerly run const_expr so all errors are reported
 590     };
 591     let _icx = push_ctxt("const_expr");
 592     Ok(match e.node {
 593         hir::ExprLit(ref lit) => const_lit(cx, e, &lit),
 594         hir::ExprBinary(b, ref e1, ref e2) => {
 595             /* Neither type is bottom, and we expect them to be unified
 596              * already, so the following is safe. */
 597             let (te1, ty) = const_expr(cx, &e1, param_substs, fn_args, trueconst)?;
 598             debug!("const_expr_unadjusted: te1={:?}, ty={:?}",
 599                    Value(te1), ty);
 600             assert!(!ty.is_simd());
 601             let is_float = ty.is_fp();
 602             let signed = ty.is_signed();
 603
 604             let (te2, ty2) = const_expr(cx, &e2, param_substs, fn_args, trueconst)?;
 605             debug!("const_expr_unadjusted: te2={:?}, ty={:?}",
 606                    Value(te2), ty2);
 607
 608             check_binary_expr_validity(cx, e, ty, te1, te2, trueconst)?;
 609
 610             unsafe { match b.node {
 611                 hir::BiAdd if is_float => llvm::LLVMConstFAdd(te1, te2),
 612                 hir::BiAdd             => llvm::LLVMConstAdd(te1, te2),
 613
 614                 hir::BiSub if is_float => llvm::LLVMConstFSub(te1, te2),
 615                 hir::BiSub             => llvm::LLVMConstSub(te1, te2),
 616
 617                 hir::BiMul if is_float => llvm::LLVMConstFMul(te1, te2),
 618                 hir::BiMul             => llvm::LLVMConstMul(te1, te2),
 619
 620                 hir::BiDiv if is_float => llvm::LLVMConstFDiv(te1, te2),
 621                 hir::BiDiv if signed   => llvm::LLVMConstSDiv(te1, te2),
 622                 hir::BiDiv             => llvm::LLVMConstUDiv(te1, te2),
 623
 624                 hir::BiRem if is_float => llvm::LLVMConstFRem(te1, te2),
 625                 hir::BiRem if signed   => llvm::LLVMConstSRem(te1, te2),
 626                 hir::BiRem             => llvm::LLVMConstURem(te1, te2),
 627
 628                 hir::BiAnd    => llvm::LLVMConstAnd(te1, te2),
 629                 hir::BiOr     => llvm::LLVMConstOr(te1, te2),
 630                 hir::BiBitXor => llvm::LLVMConstXor(te1, te2),
 631                 hir::BiBitAnd => llvm::LLVMConstAnd(te1, te2),
 632                 hir::BiBitOr  => llvm::LLVMConstOr(te1, te2),
 633                 hir::BiShl    => {
 634                     let te2 = base::cast_shift_const_rhs(b.node, te1, te2);
 635                     llvm::LLVMConstShl(te1, te2)
 636                 },
 637                 hir::BiShr    => {
 638                     let te2 = base::cast_shift_const_rhs(b.node, te1, te2);
 639                     if signed { llvm::LLVMConstAShr(te1, te2) }
 640                     else      { llvm::LLVMConstLShr(te1, te2) }
 641                 },
 642                 hir::BiEq | hir::BiNe | hir::BiLt | hir::BiLe | hir::BiGt | hir::BiGe => {
 643                     if is_float {
 644                         let cmp = base::bin_op_to_fcmp_predicate(b.node);
 645                         ConstFCmp(cmp, te1, te2)
 646                     } else {
 647                         let cmp = base::bin_op_to_icmp_predicate(b.node, signed);
 648                         ConstICmp(cmp, te1, te2)
 649                     }
 650                 },
 651             } } // unsafe { match b.node {
 652         },
 653         hir::ExprUnary(u, ref inner_e) => {
 654             let (te, ty) = const_expr(cx, &inner_e, param_substs, fn_args, trueconst)?;
 655
 656             check_unary_expr_validity(cx, e, ty, te, trueconst)?;
 657
 658             let is_float = ty.is_fp();
 659             unsafe { match u {
 660                 hir::UnDeref           => const_deref(cx, te, ty).0,
 661                 hir::UnNot             => llvm::LLVMConstNot(te),
 662                 hir::UnNeg if is_float => llvm::LLVMConstFNeg(te),
 663                 hir::UnNeg             => llvm::LLVMConstNeg(te),
 664             } }
 665         },
 666         hir::ExprField(ref base, field) => {
 667             let (bv, bt) = const_expr(cx, &base, param_substs, fn_args, trueconst)?;
 668             let brepr = adt::represent_type(cx, bt);
 669             let vinfo = VariantInfo::from_ty(cx.tcx(), bt, None);
 670             let ix = vinfo.field_index(field.node);
 671             adt::const_get_field(&brepr, bv, vinfo.discr, ix)
 672         },
 673         hir::ExprTupField(ref base, idx) => {
 674             let (bv, bt) = const_expr(cx, &base, param_substs, fn_args, trueconst)?;
 675             let brepr = adt::represent_type(cx, bt);
 676             let vinfo = VariantInfo::from_ty(cx.tcx(), bt, None);
 677             adt::const_get_field(&brepr, bv, vinfo.discr, idx.node)
 678         },
 679         hir::ExprIndex(ref base, ref index) => {
 680             let (bv, bt) = const_expr(cx, &base, param_substs, fn_args, trueconst)?;
 681             let iv = const_expr(cx, &index, param_substs, fn_args, TrueConst::Yes)?.0;
 682             let iv = if let Some(iv) = const_to_opt_uint(iv) {
 683                 iv
 684             } else {
 685                 span_bug!(index.span, "index is not an integer-constant expression");
 686             };
 687             let (arr, len) = match bt.sty {
 688                 ty::TyArray(_, u) => (bv, C_uint(cx, u)),
 689                 ty::TySlice(..) | ty::TyStr => {
 690                     let e1 = const_get_elt(bv, &[0]);
 691                     (load_const(cx, e1, bt), const_get_elt(bv, &[1]))
 692                 },
 693                 ty::TyRef(_, mt) => match mt.ty.sty {
 694                     ty::TyArray(_, u) => {
 695                         (load_const(cx, bv, mt.ty), C_uint(cx, u))
 696                     },
 697                     _ => span_bug!(base.span,
 698                                    "index-expr base must be a vector \
 699                                     or string type, found {:?}",
 700                                    bt),
 701                 },
 702                 _ => span_bug!(base.span,
 703                                "index-expr base must be a vector \
 704                                 or string type, found {:?}",
 705                                bt),
 706             };
 707
 708             let len = unsafe { llvm::LLVMConstIntGetZExtValue(len) as u64 };
 709             let len = match bt.sty {
 710                 ty::TyBox(ty) | ty::TyRef(_, ty::TypeAndMut{ty, ..}) => match ty.sty {
 711                     ty::TyStr => {
 712                         assert!(len > 0);
 713                         len - 1
 714                     },
 715                     _ => len,
 716                 },
 717                 _ => len,
 718             };
 719             if iv >= len {
 720                 // FIXME #3170: report this earlier on in the const-eval
 721                 // pass. Reporting here is a bit late.
 722                 span_err!(cx.sess(), e.span, E0515,
 723                           "const index-expr is out of bounds");
 724                 C_undef(val_ty(arr).element_type())
 725             } else {
 726                 const_get_elt(arr, &[iv as c_uint])
 727             }
 728         },
 729         hir::ExprCast(ref base, _) => {
 730             let t_cast = ety;
 731             let llty = type_of::type_of(cx, t_cast);
 732             let (v, t_expr) = const_expr(cx, &base, param_substs, fn_args, trueconst)?;
 733             debug!("trans_const_cast({:?} as {:?})", t_expr, t_cast);
 734             if expr::cast_is_noop(cx.tcx(), base, t_expr, t_cast) {
 735                 return Ok(v);
 736             }
 737             if type_is_fat_ptr(cx.tcx(), t_expr) {
 738                 // Fat pointer casts.
 739                 let t_cast_inner =
 740                     t_cast.builtin_deref(true, ty::NoPreference).expect("cast to non-pointer").ty;
 741                 let ptr_ty = type_of::in_memory_type_of(cx, t_cast_inner).ptr_to();
 742                 let addr = ptrcast(const_get_elt(v, &[abi::FAT_PTR_ADDR as u32]),
 743                                    ptr_ty);
 744                 if type_is_fat_ptr(cx.tcx(), t_cast) {
 745                     let info = const_get_elt(v, &[abi::FAT_PTR_EXTRA as u32]);
 746                     return Ok(C_struct(cx, &[addr, info], false))
 747                 } else {
 748                     return Ok(addr);
 749                 }
 750             }
 751             unsafe { match (
 752                 CastTy::from_ty(t_expr).expect("bad input type for cast"),
 753                 CastTy::from_ty(t_cast).expect("bad output type for cast"),
 754             ) {
 755                 (CastTy::Int(IntTy::CEnum), CastTy::Int(_)) => {
 756                     let repr = adt::represent_type(cx, t_expr);
 757                     let discr = adt::const_get_discrim(&repr, v);
 758                     let iv = C_integral(cx.int_type(), discr.0, false);
 759                     let s = adt::is_discr_signed(&repr) as Bool;
 760                     llvm::LLVMConstIntCast(iv, llty.to_ref(), s)
 761                 },
 762                 (CastTy::Int(_), CastTy::Int(_)) => {
 763                     let s = t_expr.is_signed() as Bool;
 764                     llvm::LLVMConstIntCast(v, llty.to_ref(), s)
 765                 },
 766                 (CastTy::Int(_), CastTy::Float) => {
 767                     if t_expr.is_signed() {
 768                         llvm::LLVMConstSIToFP(v, llty.to_ref())
 769                     } else {
 770                         llvm::LLVMConstUIToFP(v, llty.to_ref())
 771                     }
 772                 },
 773                 (CastTy::Float, CastTy::Float) => llvm::LLVMConstFPCast(v, llty.to_ref()),
 774                 (CastTy::Float, CastTy::Int(IntTy::I)) => llvm::LLVMConstFPToSI(v, llty.to_ref()),
 775                 (CastTy::Float, CastTy::Int(_)) => llvm::LLVMConstFPToUI(v, llty.to_ref()),
 776                 (CastTy::Ptr(_), CastTy::Ptr(_)) | (CastTy::FnPtr, CastTy::Ptr(_))
 777                 | (CastTy::RPtr(_), CastTy::Ptr(_)) => {
 778                     ptrcast(v, llty)
 779                 },
 780                 (CastTy::FnPtr, CastTy::FnPtr) => ptrcast(v, llty), // isn't this a coercion?
 781                 (CastTy::Int(_), CastTy::Ptr(_)) => llvm::LLVMConstIntToPtr(v, llty.to_ref()),
 782                 (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) => {
 783                   llvm::LLVMConstPtrToInt(v, llty.to_ref())
 784                 },
 785                 _ => {
 786                   span_bug!(e.span, "bad combination of types for cast")
 787                 },
 788             } } // unsafe { match ( ... ) {
 789         },
 790         hir::ExprAddrOf(hir::MutImmutable, ref sub) => {
 791             // If this is the address of some static, then we need to return
 792             // the actual address of the static itself (short circuit the rest
 793             // of const eval).
 794             let mut cur = sub;
 795             loop {
 796                 match cur.node {
 797                     hir::ExprBlock(ref blk) => {
 798                         if let Some(ref sub) = blk.expr {
 799                             cur = sub;
 800                         } else {
 801                             break;
 802                         }
 803                     },
 804                     _ => break,
 805                 }
 806             }
 807             let opt_def = cx.tcx().def_map.borrow().get(&cur.id).map(|d| d.full_def());
 808             if let Some(Def::Static(def_id, _)) = opt_def {
 809                 get_static(cx, def_id).val
 810             } else {
 811                 // If this isn't the address of a static, then keep going through
 812                 // normal constant evaluation.
 813                 let (v, ty) = const_expr(cx, &sub, param_substs, fn_args, trueconst)?;
 814                 addr_of(cx, v, type_of::align_of(cx, ty), "ref")
 815             }
 816         },
 817         hir::ExprAddrOf(hir::MutMutable, ref sub) => {
 818             let (v, ty) = const_expr(cx, &sub, param_substs, fn_args, trueconst)?;
 819             addr_of_mut(cx, v, type_of::align_of(cx, ty), "ref_mut_slice")
 820         },
 821         hir::ExprTup(ref es) => {
 822             let repr = adt::represent_type(cx, ety);
 823             let vals = map_list(&es[..])?;
 824             adt::trans_const(cx, &repr, Disr(0), &vals[..])
 825         },
 826         hir::ExprStruct(_, ref fs, ref base_opt) => {
 827             let repr = adt::represent_type(cx, ety);
 828
 829             let base_val = match *base_opt {
 830                 Some(ref base) => Some(const_expr(
 831                     cx,
 832                     &base,
 833                     param_substs,
 834                     fn_args,
 835                     trueconst,
 836                 )?),
 837                 None => None
 838             };
 839
 840             let VariantInfo { discr, fields } = VariantInfo::of_node(cx.tcx(), ety, e.id);
 841             let cs = fields.iter().enumerate().map(|(ix, &Field(f_name, _))| {
 842                 match (fs.iter().find(|f| f_name == f.name.node), base_val) {
 843                     (Some(ref f), _) => {
 844                         const_expr(cx, &f.expr, param_substs, fn_args, trueconst).map(|(l, _)| l)
 845                     },
 846                     (_, Some((bv, _))) => Ok(adt::const_get_field(&repr, bv, discr, ix)),
 847                     (_, None) => span_bug!(e.span, "missing struct field"),
 848                 }
 849             })
 850             .collect::<Vec<Result<_, ConstEvalFailure>>>()
 851             .into_iter()
 852             .collect::<Result<Vec<_>,ConstEvalFailure>>();
 853             let cs = cs?;
 854             if ety.is_simd() {
 855                 C_vector(&cs[..])
 856             } else {
 857                 adt::trans_const(cx, &repr, discr, &cs[..])
 858             }
 859         },
 860         hir::ExprVec(ref es) => {
 861             let unit_ty = ety.sequence_element_type(cx.tcx());
 862             let llunitty = type_of::type_of(cx, unit_ty);
 863             let vs = es.iter()
 864                        .map(|e| const_expr(
 865                            cx,
 866                            &e,
 867                            param_substs,
 868                            fn_args,
 869                            trueconst,
 870                        ).map(|(l, _)| l))
 871                        .collect::<Vec<Result<_, ConstEvalFailure>>>()
 872                        .into_iter()
 873                        .collect::<Result<Vec<_>, ConstEvalFailure>>();
 874             let vs = vs?;
 875             // If the vector contains enums, an LLVM array won't work.
 876             if vs.iter().any(|vi| val_ty(*vi) != llunitty) {
 877                 C_struct(cx, &vs[..], false)
 878             } else {
 879                 C_array(llunitty, &vs[..])
 880             }
 881         },
 882         hir::ExprRepeat(ref elem, ref count) => {
 883             let unit_ty = ety.sequence_element_type(cx.tcx());
 884             let llunitty = type_of::type_of(cx, unit_ty);
 885             let n = eval_repeat_count(cx.tcx(), count);
 886             let unit_val = const_expr(cx, &elem, param_substs, fn_args, trueconst)?.0;
 887             let vs = vec![unit_val; n];
 888             if val_ty(unit_val) != llunitty {
 889                 C_struct(cx, &vs[..], false)
 890             } else {
 891                 C_array(llunitty, &vs[..])
 892             }
 893         },
 894         hir::ExprPath(..) => {
 895             let def = cx.tcx().def_map.borrow().get(&e.id).unwrap().full_def();
 896             match def {
 897                 Def::Local(_, id) => {
 898                     if let Some(val) = fn_args.and_then(|args| args.get(&id).cloned()) {
 899                         val
 900                     } else {
 901                         span_bug!(e.span, "const fn argument not found")
 902                     }
 903                 }
 904                 Def::Fn(..) | Def::Method(..) => C_nil(cx),
 905                 Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 906                     load_const(cx, get_const_val(cx, def_id, e, param_substs)?,
 907                                ety)
 908                 }
 909                 Def::Variant(enum_did, variant_did) => {
 910                     let vinfo = cx.tcx().lookup_adt_def(enum_did).variant_with_id(variant_did);
 911                     match vinfo.kind() {
 912                         ty::VariantKind::Unit => {
 913                             let repr = adt::represent_type(cx, ety);
 914                             adt::trans_const(cx, &repr, Disr::from(vinfo.disr_val), &[])
 915                         }
 916                         ty::VariantKind::Tuple => C_nil(cx),
 917                         ty::VariantKind::Struct => {
 918                             span_bug!(e.span, "path-expr refers to a dict variant!")
 919                         }
 920                     }
 921                 }
 922                 // Unit struct or ctor.
 923                 Def::Struct(..) => C_null(type_of::type_of(cx, ety)),
 924                 _ => {
 925                     span_bug!(e.span, "expected a const, fn, struct, \
 926                                        or variant def")
 927                 }
 928             }
 929         },
 930         hir::ExprCall(ref callee, ref args) => {
 931             let mut callee = &**callee;
 932             loop {
 933                 callee = match callee.node {
 934                     hir::ExprBlock(ref block) => match block.expr {
 935                         Some(ref tail) => &tail,
 936                         None => break,
 937                     },
 938                     _ => break,
 939                 };
 940             }
 941             let def = cx.tcx().def_map.borrow()[&callee.id].full_def();
 942             let arg_vals = map_list(args)?;
 943             match def {
 944                 Def::Fn(did) | Def::Method(did) => {
 945                     const_fn_call(
 946                         cx,
 947                         did,
 948                         cx.tcx().node_id_item_substs(callee.id).substs,
 949                         &arg_vals,
 950                         param_substs,
 951                         trueconst,
 952                     )?
 953                 }
 954                 Def::Struct(..) => {
 955                     if ety.is_simd() {
 956                         C_vector(&arg_vals[..])
 957                     } else {
 958                         let repr = adt::represent_type(cx, ety);
 959                         adt::trans_const(cx, &repr, Disr(0), &arg_vals[..])
 960                     }
 961                 }
 962                 Def::Variant(enum_did, variant_did) => {
 963                     let repr = adt::represent_type(cx, ety);
 964                     let vinfo = cx.tcx().lookup_adt_def(enum_did).variant_with_id(variant_did);
 965                     adt::trans_const(cx,
 966                                      &repr,
 967                                      Disr::from(vinfo.disr_val),
 968                                      &arg_vals[..])
 969                 }
 970                 _ => span_bug!(e.span, "expected a struct, variant, or const fn def"),
 971             }
 972         },
 973         hir::ExprMethodCall(_, _, ref args) => {
 974             let arg_vals = map_list(args)?;
 975             let method_call = ty::MethodCall::expr(e.id);
 976             let method = cx.tcx().tables.borrow().method_map[&method_call];
 977             const_fn_call(cx, method.def_id, method.substs.clone(),
 978                           &arg_vals, param_substs, trueconst)?
 979         },
 980         hir::ExprType(ref e, _) => const_expr(cx, &e, param_substs, fn_args, trueconst)?.0,
 981         hir::ExprBlock(ref block) => {
 982             match block.expr {
 983                 Some(ref expr) => const_expr(
 984                     cx,
 985                     &expr,
 986                     param_substs,
 987                     fn_args,
 988                     trueconst,
 989                 )?.0,
 990                 None => C_nil(cx),
 991             }
 992         },
 993         hir::ExprClosure(_, ref decl, ref body) => {
 994             match ety.sty {
 995                 ty::TyClosure(def_id, ref substs) => {
 996                     closure::trans_closure_expr(closure::Dest::Ignore(cx),
 997                                                 decl,
 998                                                 body,
 999                                                 e.id,
1000                                                 def_id,
1001                                                 substs);
1002                 }
1003                 _ =>
1004                     span_bug!(
1005                         e.span,
1006                         "bad type for closure expr: {:?}", ety)
1007             }
1008             C_null(type_of::type_of(cx, ety))
1009         },
1010         _ => span_bug!(e.span,
1011                        "bad constant expression type in consts::const_expr"),
1012     })
1013 }
1014
1015 pub fn get_static<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, def_id: DefId)
1016                             -> Datum<'tcx, Lvalue> {
1017     let ty = ccx.tcx().lookup_item_type(def_id).ty;
1018
1019     let instance = Instance::mono(ccx.tcx(), def_id);
1020     if let Some(&g) = ccx.instances().borrow().get(&instance) {
1021         return Datum::new(g, ty, Lvalue::new("static"));
1022     }
1023
1024     let g = if let Some(id) = ccx.tcx().map.as_local_node_id(def_id) {
1025         let llty = type_of::type_of(ccx, ty);
1026         match ccx.tcx().map.get(id) {
1027             hir_map::NodeItem(&hir::Item {
1028                 ref attrs, span, node: hir::ItemStatic(..), ..
1029             }) => {
1030                 // If this static came from an external crate, then
1031                 // we need to get the symbol from metadata instead of
1032                 // using the current crate's name/version
1033                 // information in the hash of the symbol
1034                 let sym = exported_name(ccx, instance, attrs);
1035                 debug!("making {}", sym);
1036
1037                 // Create the global before evaluating the initializer;
1038                 // this is necessary to allow recursive statics.
1039                 let g = declare::define_global(ccx, &sym, llty).unwrap_or_else(|| {
1040                     ccx.sess().span_fatal(span,
1041                         &format!("symbol `{}` is already defined", sym))
1042                 });
1043
1044                 ccx.item_symbols().borrow_mut().insert(id, sym);
1045                 g
1046             }
1047
1048             hir_map::NodeForeignItem(&hir::ForeignItem {
1049                 ref attrs, name, span, node: hir::ForeignItemStatic(..), ..
1050             }) => {
1051                 let ident = imported_name(name, attrs);
1052                 let g = if let Some(name) =
1053                         attr::first_attr_value_str_by_name(&attrs, "linkage") {
1054                     // If this is a static with a linkage specified, then we need to handle
1055                     // it a little specially. The typesystem prevents things like &T and
1056                     // extern "C" fn() from being non-null, so we can't just declare a
1057                     // static and call it a day. Some linkages (like weak) will make it such
1058                     // that the static actually has a null value.
1059                     let linkage = match base::llvm_linkage_by_name(&name) {
1060                         Some(linkage) => linkage,
1061                         None => {
1062                             ccx.sess().span_fatal(span, "invalid linkage specified");
1063                         }
1064                     };
1065                     let llty2 = match ty.sty {
1066                         ty::TyRawPtr(ref mt) => type_of::type_of(ccx, mt.ty),
1067                         _ => {
1068                             ccx.sess().span_fatal(span, "must have type `*const T` or `*mut T`");
1069                         }
1070                     };
1071                     unsafe {
1072                         // Declare a symbol `foo` with the desired linkage.
1073                         let g1 = declare::declare_global(ccx, &ident, llty2);
1074                         llvm::SetLinkage(g1, linkage);
1075
1076                         // Declare an internal global `extern_with_linkage_foo` which
1077                         // is initialized with the address of `foo`.  If `foo` is
1078                         // discarded during linking (for example, if `foo` has weak
1079                         // linkage and there are no definitions), then
1080                         // `extern_with_linkage_foo` will instead be initialized to
1081                         // zero.
1082                         let mut real_name = "_rust_extern_with_linkage_".to_string();
1083                         real_name.push_str(&ident);
1084                         let g2 = declare::define_global(ccx, &real_name, llty).unwrap_or_else(||{
1085                             ccx.sess().span_fatal(span,
1086                                 &format!("symbol `{}` is already defined", ident))
1087                         });
1088                         llvm::SetLinkage(g2, llvm::InternalLinkage);
1089                         llvm::LLVMSetInitializer(g2, g1);
1090                         g2
1091                     }
1092                 } else {
1093                     // Generate an external declaration.
1094                     declare::declare_global(ccx, &ident, llty)
1095                 };
1096
1097                 for attr in attrs {
1098                     if attr.check_name("thread_local") {
1099                         llvm::set_thread_local(g, true);
1100                     }
1101                 }
1102
1103                 g
1104             }
1105
1106             item => bug!("get_static: expected static, found {:?}", item)
1107         }
1108     } else {
1109         // FIXME(nagisa): perhaps the map of externs could be offloaded to llvm somehow?
1110         // FIXME(nagisa): investigate whether it can be changed into define_global
1111         let name = ccx.sess().cstore.item_symbol(def_id);
1112         let g = declare::declare_global(ccx, &name, type_of::type_of(ccx, ty));
1113         // Thread-local statics in some other crate need to *always* be linked
1114         // against in a thread-local fashion, so we need to be sure to apply the
1115         // thread-local attribute locally if it was present remotely. If we
1116         // don't do this then linker errors can be generated where the linker
1117         // complains that one object files has a thread local version of the
1118         // symbol and another one doesn't.
1119         for attr in ccx.tcx().get_attrs(def_id).iter() {
1120             if attr.check_name("thread_local") {
1121                 llvm::set_thread_local(g, true);
1122             }
1123         }
1124         if ccx.use_dll_storage_attrs() {
1125             llvm::SetDLLStorageClass(g, llvm::DLLImportStorageClass);
1126         }
1127         g
1128     };
1129
1130     ccx.instances().borrow_mut().insert(instance, g);
1131     Datum::new(g, ty, Lvalue::new("static"))
1132 }
1133
1134 pub fn trans_static(ccx: &CrateContext,
1135                     m: hir::Mutability,
1136                     expr: &hir::Expr,
1137                     id: ast::NodeId,
1138                     attrs: &[ast::Attribute])
1139                     -> Result<ValueRef, ConstEvalErr> {
1140
1141     if collector::collecting_debug_information(ccx) {
1142         ccx.record_translation_item_as_generated(TransItem::Static(id));
1143     }
1144
1145     unsafe {
1146         let _icx = push_ctxt("trans_static");
1147         let def_id = ccx.tcx().map.local_def_id(id);
1148         let datum = get_static(ccx, def_id);
1149
1150         let empty_substs = ccx.tcx().mk_substs(Substs::empty());
1151         let (v, _) = const_expr(
1152             ccx,
1153             expr,
1154             empty_substs,
1155             None,
1156             TrueConst::Yes,
1157         ).map_err(|e| e.into_inner())?;
1158
1159         // boolean SSA values are i1, but they have to be stored in i8 slots,
1160         // otherwise some LLVM optimization passes don't work as expected
1161         let mut val_llty = val_ty(v);
1162         let v = if val_llty == Type::i1(ccx) {
1163             val_llty = Type::i8(ccx);
1164             llvm::LLVMConstZExt(v, val_llty.to_ref())
1165         } else {
1166             v
1167         };
1168
1169         let llty = type_of::type_of(ccx, datum.ty);
1170         let g = if val_llty == llty {
1171             datum.val
1172         } else {
1173             // If we created the global with the wrong type,
1174             // correct the type.
1175             let empty_string = CString::new("").unwrap();
1176             let name_str_ref = CStr::from_ptr(llvm::LLVMGetValueName(datum.val));
1177             let name_string = CString::new(name_str_ref.to_bytes()).unwrap();
1178             llvm::LLVMSetValueName(datum.val, empty_string.as_ptr());
1179             let new_g = llvm::LLVMGetOrInsertGlobal(
1180                 ccx.llmod(), name_string.as_ptr(), val_llty.to_ref());
1181             // To avoid breaking any invariants, we leave around the old
1182             // global for the moment; we'll replace all references to it
1183             // with the new global later. (See base::trans_crate.)
1184             ccx.statics_to_rauw().borrow_mut().push((datum.val, new_g));
1185             new_g
1186         };
1187         llvm::LLVMSetAlignment(g, type_of::align_of(ccx, datum.ty));
1188         llvm::LLVMSetInitializer(g, v);
1189
1190         // As an optimization, all shared statics which do not have interior
1191         // mutability are placed into read-only memory.
1192         if m != hir::MutMutable {
1193             let tcontents = datum.ty.type_contents(ccx.tcx());
1194             if !tcontents.interior_unsafe() {
1195                 llvm::LLVMSetGlobalConstant(g, llvm::True);
1196             }
1197         }
1198
1199         debuginfo::create_global_var_metadata(ccx, id, g);
1200
1201         if attr::contains_name(attrs,
1202                                "thread_local") {
1203             llvm::set_thread_local(g, true);
1204         }
1205         Ok(g)
1206     }
1207 }