src/librustc_trans/trans/mir/lvalue.rs

   1 // Copyright 2012-2014 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 use llvm::ValueRef;
  12 use rustc::middle::ty::{self, Ty};
  13 use rustc_mir::repr as mir;
  14 use rustc_mir::tcx::LvalueTy;
  15 use trans::adt;
  16 use trans::base;
  17 use trans::build;
  18 use trans::common::{self, Block};
  19 use trans::debuginfo::DebugLoc;
  20 use trans::machine;
  21
  22 use std::ptr;
  23
  24 use super::{MirContext, TempRef};
  25
  26 #[derive(Copy, Clone)]
  27 pub struct LvalueRef<'tcx> {
  28     /// Pointer to the contents of the lvalue
  29     pub llval: ValueRef,
  30
  31     /// This lvalue's extra data if it is unsized, or null
  32     pub llextra: ValueRef,
  33
  34     /// Monomorphized type of this lvalue, including variant information
  35     pub ty: LvalueTy<'tcx>,
  36 }
  37
  38 impl<'tcx> LvalueRef<'tcx> {
  39     pub fn new_sized(llval: ValueRef, lvalue_ty: LvalueTy<'tcx>) -> LvalueRef<'tcx> {
  40         LvalueRef { llval: llval, llextra: ptr::null_mut(), ty: lvalue_ty }
  41     }
  42
  43     pub fn alloca<'bcx>(bcx: Block<'bcx, 'tcx>,
  44                         ty: Ty<'tcx>,
  45                         name: &str)
  46                         -> LvalueRef<'tcx>
  47     {
  48         let lltemp = base::alloc_ty(bcx, ty, name);
  49         LvalueRef::new_sized(lltemp, LvalueTy::from_ty(ty))
  50     }
  51 }
  52
  53 impl<'bcx, 'tcx> MirContext<'bcx, 'tcx> {
  54     pub fn lvalue_len(&mut self,
  55                       bcx: Block<'bcx, 'tcx>,
  56                       lvalue: LvalueRef<'tcx>)
  57                       -> ValueRef {
  58         match lvalue.ty.to_ty(bcx.tcx()).sty {
  59             ty::TyArray(_, n) => common::C_uint(bcx.ccx(), n),
  60             ty::TySlice(_) | ty::TyStr => {
  61                 assert!(lvalue.llextra != ptr::null_mut());
  62                 lvalue.llextra
  63             }
  64             _ => bcx.sess().bug("unexpected type in get_base_and_len"),
  65         }
  66     }
  67
  68     pub fn trans_lvalue(&mut self,
  69                         bcx: Block<'bcx, 'tcx>,
  70                         lvalue: &mir::Lvalue<'tcx>)
  71                         -> LvalueRef<'tcx> {
  72         debug!("trans_lvalue(lvalue={:?})", lvalue);
  73
  74         let fcx = bcx.fcx;
  75         let ccx = fcx.ccx;
  76         let tcx = bcx.tcx();
  77         match *lvalue {
  78             mir::Lvalue::Var(index) => self.vars[index as usize],
  79             mir::Lvalue::Temp(index) => match self.temps[index as usize] {
  80                 TempRef::Lvalue(lvalue) =>
  81                     lvalue,
  82                 TempRef::Operand(..) =>
  83                     tcx.sess.bug(&format!("using operand temp {:?} as lvalue", lvalue)),
  84             },
  85             mir::Lvalue::Arg(index) => self.args[index as usize],
  86             mir::Lvalue::Static(def_id) => {
  87                 let const_ty = self.mir.lvalue_ty(tcx, lvalue);
  88                 LvalueRef::new_sized(
  89                     common::get_static_val(ccx, def_id, const_ty.to_ty(tcx)),
  90                     const_ty)
  91             },
  92             mir::Lvalue::ReturnPointer => {
  93                 let return_ty = bcx.monomorphize(&self.mir.return_ty);
  94                 let llval = fcx.get_ret_slot(bcx, return_ty, "return");
  95                 LvalueRef::new_sized(llval, LvalueTy::from_ty(return_ty.unwrap()))
  96             }
  97             mir::Lvalue::Projection(ref projection) => {
  98                 let tr_base = self.trans_lvalue(bcx, &projection.base);
  99                 let projected_ty = tr_base.ty.projection_ty(tcx, &projection.elem);
 100                 let (llprojected, llextra) = match projection.elem {
 101                     mir::ProjectionElem::Deref => {
 102                         let base_ty = tr_base.ty.to_ty(tcx);
 103                         if common::type_is_sized(tcx, projected_ty.to_ty(tcx)) {
 104                             (base::load_ty(bcx, tr_base.llval, base_ty),
 105                              ptr::null_mut())
 106                         } else {
 107                             base::load_fat_ptr(bcx, tr_base.llval, base_ty)
 108                         }
 109                     }
 110                     mir::ProjectionElem::Field(ref field) => {
 111                         let base_ty = tr_base.ty.to_ty(tcx);
 112                         let base_repr = adt::represent_type(ccx, base_ty);
 113                         let discr = match tr_base.ty {
 114                             LvalueTy::Ty { .. } => 0,
 115                             LvalueTy::Downcast { adt_def: _, substs: _, variant_index: v } => v,
 116                         };
 117                         let discr = discr as u64;
 118                         (adt::trans_field_ptr(bcx, &base_repr, tr_base.llval, discr, field.index()),
 119                          if common::type_is_sized(tcx, projected_ty.to_ty(tcx)) {
 120                              ptr::null_mut()
 121                          } else {
 122                              tr_base.llextra
 123                          })
 124                     }
 125                     mir::ProjectionElem::Index(ref index) => {
 126                         let index = self.trans_operand(bcx, index);
 127                         let llindex = self.prepare_index(bcx, index.immediate());
 128                         (build::InBoundsGEP(bcx, tr_base.llval, &[llindex]),
 129                          ptr::null_mut())
 130                     }
 131                     mir::ProjectionElem::ConstantIndex { offset,
 132                                                          from_end: false,
 133                                                          min_length: _ } => {
 134                         let lloffset = common::C_u32(bcx.ccx(), offset);
 135                         let llindex = self.prepare_index(bcx, lloffset);
 136                         (build::InBoundsGEP(bcx, tr_base.llval, &[llindex]),
 137                          ptr::null_mut())
 138                     }
 139                     mir::ProjectionElem::ConstantIndex { offset,
 140                                                          from_end: true,
 141                                                          min_length: _ } => {
 142                         let lloffset = common::C_u32(bcx.ccx(), offset);
 143                         let lllen = self.lvalue_len(bcx, tr_base);
 144                         let llindex = build::Sub(bcx, lllen, lloffset, DebugLoc::None);
 145                         let llindex = self.prepare_index(bcx, llindex);
 146                         (build::InBoundsGEP(bcx, tr_base.llval, &[llindex]),
 147                          ptr::null_mut())
 148                     }
 149                     mir::ProjectionElem::Downcast(..) => {
 150                         (tr_base.llval, tr_base.llextra)
 151                     }
 152                 };
 153                 LvalueRef {
 154                     llval: llprojected,
 155                     llextra: llextra,
 156                     ty: projected_ty,
 157                 }
 158             }
 159         }
 160     }
 161
 162     /// Adjust the bitwidth of an index since LLVM is less forgiving
 163     /// than we are.
 164     ///
 165     /// nmatsakis: is this still necessary? Not sure.
 166     fn prepare_index(&mut self,
 167                      bcx: Block<'bcx, 'tcx>,
 168                      llindex: ValueRef)
 169                      -> ValueRef
 170     {
 171         let ccx = bcx.ccx();
 172         let index_size = machine::llbitsize_of_real(bcx.ccx(), common::val_ty(llindex));
 173         let int_size = machine::llbitsize_of_real(bcx.ccx(), ccx.int_type());
 174         if index_size < int_size {
 175             build::ZExt(bcx, llindex, ccx.int_type())
 176         } else if index_size > int_size {
 177             build::Trunc(bcx, llindex, ccx.int_type())
 178         } else {
 179             llindex
 180         }
 181     }
 182 }