src/librustc_trans/mir/operand.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::ty::Ty;
  13 use rustc::ty::layout::Layout;
  14 use rustc::mir;
  15 use rustc_data_structures::indexed_vec::Idx;
  16
  17 use base;
  18 use common;
  19 use builder::Builder;
  20 use value::Value;
  21 use type_of;
  22 use type_::Type;
  23
  24 use std::fmt;
  25
  26 use super::{MirContext, LocalRef};
  27 use super::lvalue::Alignment;
  28
  29 /// The representation of a Rust value. The enum variant is in fact
  30 /// uniquely determined by the value's type, but is kept as a
  31 /// safety check.
  32 #[derive(Copy, Clone)]
  33 pub enum OperandValue {
  34     /// A reference to the actual operand. The data is guaranteed
  35     /// to be valid for the operand's lifetime.
  36     Ref(ValueRef, Alignment),
  37     /// A single LLVM value.
  38     Immediate(ValueRef),
  39     /// A pair of immediate LLVM values. Used by fat pointers too.
  40     Pair(ValueRef, ValueRef)
  41 }
  42
  43 /// An `OperandRef` is an "SSA" reference to a Rust value, along with
  44 /// its type.
  45 ///
  46 /// NOTE: unless you know a value's type exactly, you should not
  47 /// generate LLVM opcodes acting on it and instead act via methods,
  48 /// to avoid nasty edge cases. In particular, using `Builder.store`
  49 /// directly is sure to cause problems -- use `MirContext.store_operand`
  50 /// instead.
  51 #[derive(Copy, Clone)]
  52 pub struct OperandRef<'tcx> {
  53     // The value.
  54     pub val: OperandValue,
  55
  56     // The type of value being returned.
  57     pub ty: Ty<'tcx>
  58 }
  59
  60 impl<'tcx> fmt::Debug for OperandRef<'tcx> {
  61     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  62         match self.val {
  63             OperandValue::Ref(r, align) => {
  64                 write!(f, "OperandRef(Ref({:?}, {:?}) @ {:?})",
  65                        Value(r), align, self.ty)
  66             }
  67             OperandValue::Immediate(i) => {
  68                 write!(f, "OperandRef(Immediate({:?}) @ {:?})",
  69                        Value(i), self.ty)
  70             }
  71             OperandValue::Pair(a, b) => {
  72                 write!(f, "OperandRef(Pair({:?}, {:?}) @ {:?})",
  73                        Value(a), Value(b), self.ty)
  74             }
  75         }
  76     }
  77 }
  78
  79 impl<'a, 'tcx> OperandRef<'tcx> {
  80     /// Asserts that this operand refers to a scalar and returns
  81     /// a reference to its value.
  82     pub fn immediate(self) -> ValueRef {
  83         match self.val {
  84             OperandValue::Immediate(s) => s,
  85             _ => bug!("not immediate: {:?}", self)
  86         }
  87     }
  88
  89     /// If this operand is a Pair, we return an
  90     /// Immediate aggregate with the two values.
  91     pub fn pack_if_pair(mut self, bcx: &Builder<'a, 'tcx>) -> OperandRef<'tcx> {
  92         if let OperandValue::Pair(a, b) = self.val {
  93             // Reconstruct the immediate aggregate.
  94             let llty = type_of::type_of(bcx.ccx, self.ty);
  95             let mut llpair = common::C_undef(llty);
  96             let elems = [a, b];
  97             for i in 0..2 {
  98                 let mut elem = elems[i];
  99                 // Extend boolean i1's to i8.
 100                 if common::val_ty(elem) == Type::i1(bcx.ccx) {
 101                     elem = bcx.zext(elem, Type::i8(bcx.ccx));
 102                 }
 103                 llpair = bcx.insert_value(llpair, elem, i);
 104             }
 105             self.val = OperandValue::Immediate(llpair);
 106         }
 107         self
 108     }
 109
 110     /// If this operand is a pair in an Immediate,
 111     /// we return a Pair with the two halves.
 112     pub fn unpack_if_pair(mut self, bcx: &Builder<'a, 'tcx>) -> OperandRef<'tcx> {
 113         if let OperandValue::Immediate(llval) = self.val {
 114             // Deconstruct the immediate aggregate.
 115             if common::type_is_imm_pair(bcx.ccx, self.ty) {
 116                 debug!("Operand::unpack_if_pair: unpacking {:?}", self);
 117
 118                 let mut a = bcx.extract_value(llval, 0);
 119                 let mut b = bcx.extract_value(llval, 1);
 120
 121                 let pair_fields = common::type_pair_fields(bcx.ccx, self.ty);
 122                 if let Some([a_ty, b_ty]) = pair_fields {
 123                     if a_ty.is_bool() {
 124                         a = bcx.trunc(a, Type::i1(bcx.ccx));
 125                     }
 126                     if b_ty.is_bool() {
 127                         b = bcx.trunc(b, Type::i1(bcx.ccx));
 128                     }
 129                 }
 130
 131                 self.val = OperandValue::Pair(a, b);
 132             }
 133         }
 134         self
 135     }
 136 }
 137
 138 impl<'a, 'tcx> MirContext<'a, 'tcx> {
 139     pub fn trans_load(&mut self,
 140                       bcx: &Builder<'a, 'tcx>,
 141                       llval: ValueRef,
 142                       align: Alignment,
 143                       ty: Ty<'tcx>)
 144                       -> OperandRef<'tcx>
 145     {
 146         debug!("trans_load: {:?} @ {:?}", Value(llval), ty);
 147
 148         let val = if common::type_is_fat_ptr(bcx.ccx, ty) {
 149             let (lldata, llextra) = base::load_fat_ptr(bcx, llval, align, ty);
 150             OperandValue::Pair(lldata, llextra)
 151         } else if common::type_is_imm_pair(bcx.ccx, ty) {
 152             let f_align = match *bcx.ccx.layout_of(ty) {
 153                 Layout::Univariant { ref variant, .. } =>
 154                     Alignment::from_packed(variant.packed) | align,
 155                 _ => align
 156             };
 157             let [a_ty, b_ty] = common::type_pair_fields(bcx.ccx, ty).unwrap();
 158             let a_ptr = bcx.struct_gep(llval, 0);
 159             let b_ptr = bcx.struct_gep(llval, 1);
 160
 161             OperandValue::Pair(
 162                 base::load_ty(bcx, a_ptr, f_align, a_ty),
 163                 base::load_ty(bcx, b_ptr, f_align, b_ty)
 164             )
 165         } else if common::type_is_immediate(bcx.ccx, ty) {
 166             OperandValue::Immediate(base::load_ty(bcx, llval, align, ty))
 167         } else {
 168             OperandValue::Ref(llval, align)
 169         };
 170
 171         OperandRef { val: val, ty: ty }
 172     }
 173
 174     pub fn trans_consume(&mut self,
 175                          bcx: &Builder<'a, 'tcx>,
 176                          lvalue: &mir::Lvalue<'tcx>)
 177                          -> OperandRef<'tcx>
 178     {
 179         debug!("trans_consume(lvalue={:?})", lvalue);
 180
 181         // watch out for locals that do not have an
 182         // alloca; they are handled somewhat differently
 183         if let mir::Lvalue::Local(index) = *lvalue {
 184             match self.locals[index] {
 185                 LocalRef::Operand(Some(o)) => {
 186                     return o;
 187                 }
 188                 LocalRef::Operand(None) => {
 189                     bug!("use of {:?} before def", lvalue);
 190                 }
 191                 LocalRef::Lvalue(..) => {
 192                     // use path below
 193                 }
 194             }
 195         }
 196
 197         // Moves out of pair fields are trivial.
 198         if let &mir::Lvalue::Projection(ref proj) = lvalue {
 199             if let mir::Lvalue::Local(index) = proj.base {
 200                 if let LocalRef::Operand(Some(o)) = self.locals[index] {
 201                     match (o.val, &proj.elem) {
 202                         (OperandValue::Pair(a, b),
 203                          &mir::ProjectionElem::Field(ref f, ty)) => {
 204                             let llval = [a, b][f.index()];
 205                             let op = OperandRef {
 206                                 val: OperandValue::Immediate(llval),
 207                                 ty: self.monomorphize(&ty)
 208                             };
 209
 210                             // Handle nested pairs.
 211                             return op.unpack_if_pair(bcx);
 212                         }
 213                         _ => {}
 214                     }
 215                 }
 216             }
 217         }
 218
 219         // for most lvalues, to consume them we just load them
 220         // out from their home
 221         let tr_lvalue = self.trans_lvalue(bcx, lvalue);
 222         let ty = tr_lvalue.ty.to_ty(bcx.tcx());
 223         self.trans_load(bcx, tr_lvalue.llval, tr_lvalue.alignment, ty)
 224     }
 225
 226     pub fn trans_operand(&mut self,
 227                          bcx: &Builder<'a, 'tcx>,
 228                          operand: &mir::Operand<'tcx>)
 229                          -> OperandRef<'tcx>
 230     {
 231         debug!("trans_operand(operand={:?})", operand);
 232
 233         match *operand {
 234             mir::Operand::Consume(ref lvalue) => {
 235                 self.trans_consume(bcx, lvalue)
 236             }
 237
 238             mir::Operand::Constant(ref constant) => {
 239                 let val = self.trans_constant(bcx, constant);
 240                 let operand = val.to_operand(bcx.ccx);
 241                 if let OperandValue::Ref(ptr, align) = operand.val {
 242                     // If this is a OperandValue::Ref to an immediate constant, load it.
 243                     self.trans_load(bcx, ptr, align, operand.ty)
 244                 } else {
 245                     operand
 246                 }
 247             }
 248         }
 249     }
 250
 251     pub fn store_operand(&mut self,
 252                          bcx: &Builder<'a, 'tcx>,
 253                          lldest: ValueRef,
 254                          align: Option<u32>,
 255                          operand: OperandRef<'tcx>) {
 256         debug!("store_operand: operand={:?}, align={:?}", operand, align);
 257         // Avoid generating stores of zero-sized values, because the only way to have a zero-sized
 258         // value is through `undef`, and store itself is useless.
 259         if common::type_is_zero_size(bcx.ccx, operand.ty) {
 260             return;
 261         }
 262         match operand.val {
 263             OperandValue::Ref(r, Alignment::Packed) =>
 264                 base::memcpy_ty(bcx, lldest, r, operand.ty, Some(1)),
 265             OperandValue::Ref(r, Alignment::AbiAligned) =>
 266                 base::memcpy_ty(bcx, lldest, r, operand.ty, align),
 267             OperandValue::Immediate(s) => {
 268                 bcx.store(base::from_immediate(bcx, s), lldest, align);
 269             }
 270             OperandValue::Pair(a, b) => {
 271                 let f_align = match *bcx.ccx.layout_of(operand.ty) {
 272                     Layout::Univariant { ref variant, .. } if variant.packed => {
 273                         Some(1)
 274                     }
 275                     _ => align
 276                 };
 277
 278                 let a = base::from_immediate(bcx, a);
 279                 let b = base::from_immediate(bcx, b);
 280                 bcx.store(a, bcx.struct_gep(lldest, 0), f_align);
 281                 bcx.store(b, bcx.struct_gep(lldest, 1), f_align);
 282             }
 283         }
 284     }
 285 }