compiler/rustc_codegen_ssa/src/mir/mod.rs

   1 use crate::traits::*;
   2 use rustc_errors::ErrorReported;
   3 use rustc_middle::mir;
   4 use rustc_middle::mir::interpret::ErrorHandled;
   5 use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt, TyAndLayout};
   6 use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
   7 use rustc_target::abi::call::{FnAbi, PassMode};
   8
   9 use std::iter;
  10
  11 use rustc_index::bit_set::BitSet;
  12 use rustc_index::vec::IndexVec;
  13
  14 use self::debuginfo::{FunctionDebugContext, PerLocalVarDebugInfo};
  15 use self::place::PlaceRef;
  16 use rustc_middle::mir::traversal;
  17
  18 use self::operand::{OperandRef, OperandValue};
  19
  20 /// Master context for codegenning from MIR.
  21 pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
  22     instance: Instance<'tcx>,
  23
  24     mir: &'tcx mir::Body<'tcx>,
  25
  26     debug_context: Option<FunctionDebugContext<Bx::DIScope, Bx::DILocation>>,
  27
  28     llfn: Bx::Function,
  29
  30     cx: &'a Bx::CodegenCx,
  31
  32     fn_abi: FnAbi<'tcx, Ty<'tcx>>,
  33
  34     /// When unwinding is initiated, we have to store this personality
  35     /// value somewhere so that we can load it and re-use it in the
  36     /// resume instruction. The personality is (afaik) some kind of
  37     /// value used for C++ unwinding, which must filter by type: we
  38     /// don't really care about it very much. Anyway, this value
  39     /// contains an alloca into which the personality is stored and
  40     /// then later loaded when generating the DIVERGE_BLOCK.
  41     personality_slot: Option<PlaceRef<'tcx, Bx::Value>>,
  42
  43     /// A backend `BasicBlock` for each MIR `BasicBlock`, created lazily
  44     /// as-needed (e.g. RPO reaching it or another block branching to it).
  45     // FIXME(eddyb) rename `llbbs` and other `ll`-prefixed things to use a
  46     // more backend-agnostic prefix such as `cg` (i.e. this would be `cgbbs`).
  47     cached_llbbs: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>>,
  48
  49     /// The funclet status of each basic block
  50     cleanup_kinds: IndexVec<mir::BasicBlock, analyze::CleanupKind>,
  51
  52     /// When targeting MSVC, this stores the cleanup info for each funclet BB.
  53     /// This is initialized at the same time as the `landing_pads` entry for the
  54     /// funclets' head block, i.e. when needed by an unwind / `cleanup_ret` edge.
  55     funclets: IndexVec<mir::BasicBlock, Option<Bx::Funclet>>,
  56
  57     /// This stores the cached landing/cleanup pad block for a given BB.
  58     // FIXME(eddyb) rename this to `eh_pads`.
  59     landing_pads: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>>,
  60
  61     /// Cached unreachable block
  62     unreachable_block: Option<Bx::BasicBlock>,
  63
  64     /// The location where each MIR arg/var/tmp/ret is stored. This is
  65     /// usually an `PlaceRef` representing an alloca, but not always:
  66     /// sometimes we can skip the alloca and just store the value
  67     /// directly using an `OperandRef`, which makes for tighter LLVM
  68     /// IR. The conditions for using an `OperandRef` are as follows:
  69     ///
  70     /// - the type of the local must be judged "immediate" by `is_llvm_immediate`
  71     /// - the operand must never be referenced indirectly
  72     ///     - we should not take its address using the `&` operator
  73     ///     - nor should it appear in a place path like `tmp.a`
  74     /// - the operand must be defined by an rvalue that can generate immediate
  75     ///   values
  76     ///
  77     /// Avoiding allocs can also be important for certain intrinsics,
  78     /// notably `expect`.
  79     locals: IndexVec<mir::Local, LocalRef<'tcx, Bx::Value>>,
  80
  81     /// All `VarDebugInfo` from the MIR body, partitioned by `Local`.
  82     /// This is `None` if no var`#[non_exhaustive]`iable debuginfo/names are needed.
  83     per_local_var_debug_info:
  84         Option<IndexVec<mir::Local, Vec<PerLocalVarDebugInfo<'tcx, Bx::DIVariable>>>>,
  85
  86     /// Caller location propagated if this function has `#[track_caller]`.
  87     caller_location: Option<OperandRef<'tcx, Bx::Value>>,
  88 }
  89
  90 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  91     pub fn monomorphize<T>(&self, value: T) -> T
  92     where
  93         T: Copy + TypeFoldable<'tcx>,
  94     {
  95         debug!("monomorphize: self.instance={:?}", self.instance);
  96         self.instance.subst_mir_and_normalize_erasing_regions(
  97             self.cx.tcx(),
  98             ty::ParamEnv::reveal_all(),
  99             value,
 100         )
 101     }
 102 }
 103
 104 enum LocalRef<'tcx, V> {
 105     Place(PlaceRef<'tcx, V>),
 106     /// `UnsizedPlace(p)`: `p` itself is a thin pointer (indirect place).
 107     /// `*p` is the fat pointer that references the actual unsized place.
 108     /// Every time it is initialized, we have to reallocate the place
 109     /// and update the fat pointer. That's the reason why it is indirect.
 110     UnsizedPlace(PlaceRef<'tcx, V>),
 111     Operand(Option<OperandRef<'tcx, V>>),
 112 }
 113
 114 impl<'a, 'tcx, V: CodegenObject> LocalRef<'tcx, V> {
 115     fn new_operand<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 116         bx: &mut Bx,
 117         layout: TyAndLayout<'tcx>,
 118     ) -> LocalRef<'tcx, V> {
 119         if layout.is_zst() {
 120             // Zero-size temporaries aren't always initialized, which
 121             // doesn't matter because they don't contain data, but
 122             // we need something in the operand.
 123             LocalRef::Operand(Some(OperandRef::new_zst(bx, layout)))
 124         } else {
 125             LocalRef::Operand(None)
 126         }
 127     }
 128 }
 129
 130 ///////////////////////////////////////////////////////////////////////////
 131
 132 pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 133     cx: &'a Bx::CodegenCx,
 134     instance: Instance<'tcx>,
 135 ) {
 136     assert!(!instance.substs.needs_infer());
 137
 138     let llfn = cx.get_fn(instance);
 139
 140     let mir = cx.tcx().instance_mir(instance.def);
 141
 142     let fn_abi = FnAbi::of_instance(cx, instance, &[]);
 143     debug!("fn_abi: {:?}", fn_abi);
 144
 145     let debug_context = cx.create_function_debug_context(instance, &fn_abi, llfn, &mir);
 146
 147     let start_llbb = Bx::append_block(cx, llfn, "start");
 148     let mut bx = Bx::build(cx, start_llbb);
 149
 150     if mir.basic_blocks().iter().any(|bb| bb.is_cleanup) {
 151         bx.set_personality_fn(cx.eh_personality());
 152     }
 153
 154     let cleanup_kinds = analyze::cleanup_kinds(&mir);
 155     // Allocate a `Block` for every basic block, except
 156     // the start block, if nothing loops back to it.
 157     let reentrant_start_block = !mir.predecessors()[mir::START_BLOCK].is_empty();
 158     let cached_llbbs: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>> =
 159         mir.basic_blocks()
 160             .indices()
 161             .map(|bb| {
 162                 if bb == mir::START_BLOCK && !reentrant_start_block {
 163                     Some(start_llbb)
 164                 } else {
 165                     None
 166                 }
 167             })
 168             .collect();
 169
 170     let mut fx = FunctionCx {
 171         instance,
 172         mir,
 173         llfn,
 174         fn_abi,
 175         cx,
 176         personality_slot: None,
 177         cached_llbbs,
 178         unreachable_block: None,
 179         cleanup_kinds,
 180         landing_pads: IndexVec::from_elem(None, mir.basic_blocks()),
 181         funclets: IndexVec::from_fn_n(|_| None, mir.basic_blocks().len()),
 182         locals: IndexVec::new(),
 183         debug_context,
 184         per_local_var_debug_info: None,
 185         caller_location: None,
 186     };
 187
 188     fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut bx);
 189
 190     // Evaluate all required consts; codegen later assumes that CTFE will never fail.
 191     let mut all_consts_ok = true;
 192     for const_ in &mir.required_consts {
 193         if let Err(err) = fx.eval_mir_constant(const_) {
 194             all_consts_ok = false;
 195             match err {
 196                 // errored or at least linted
 197                 ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted => {}
 198                 ErrorHandled::TooGeneric => {
 199                     span_bug!(const_.span, "codgen encountered polymorphic constant: {:?}", err)
 200                 }
 201             }
 202         }
 203     }
 204     if !all_consts_ok {
 205         // We leave the IR in some half-built state here, and rely on this code not even being
 206         // submitted to LLVM once an error was raised.
 207         return;
 208     }
 209
 210     let memory_locals = analyze::non_ssa_locals(&fx);
 211
 212     // Allocate variable and temp allocas
 213     fx.locals = {
 214         let args = arg_local_refs(&mut bx, &mut fx, &memory_locals);
 215
 216         let mut allocate_local = |local| {
 217             let decl = &mir.local_decls[local];
 218             let layout = bx.layout_of(fx.monomorphize(decl.ty));
 219             assert!(!layout.ty.has_erasable_regions(cx.tcx()));
 220
 221             if local == mir::RETURN_PLACE && fx.fn_abi.ret.is_indirect() {
 222                 debug!("alloc: {:?} (return place) -> place", local);
 223                 let llretptr = bx.get_param(0);
 224                 return LocalRef::Place(PlaceRef::new_sized(llretptr, layout));
 225             }
 226
 227             if memory_locals.contains(local) {
 228                 debug!("alloc: {:?} -> place", local);
 229                 if layout.is_unsized() {
 230                     LocalRef::UnsizedPlace(PlaceRef::alloca_unsized_indirect(&mut bx, layout))
 231                 } else {
 232                     LocalRef::Place(PlaceRef::alloca(&mut bx, layout))
 233                 }
 234             } else {
 235                 debug!("alloc: {:?} -> operand", local);
 236                 LocalRef::new_operand(&mut bx, layout)
 237             }
 238         };
 239
 240         let retptr = allocate_local(mir::RETURN_PLACE);
 241         iter::once(retptr)
 242             .chain(args.into_iter())
 243             .chain(mir.vars_and_temps_iter().map(allocate_local))
 244             .collect()
 245     };
 246
 247     // Apply debuginfo to the newly allocated locals.
 248     fx.debug_introduce_locals(&mut bx);
 249
 250     // Branch to the START block, if it's not the entry block.
 251     if reentrant_start_block {
 252         bx.br(fx.llbb(mir::START_BLOCK));
 253     }
 254
 255     // Codegen the body of each block using reverse postorder
 256     // FIXME(eddyb) reuse RPO iterator between `analysis` and this.
 257     for (bb, _) in traversal::reverse_postorder(&mir) {
 258         fx.codegen_block(bb);
 259     }
 260 }
 261
 262 /// Produces, for each argument, a `Value` pointing at the
 263 /// argument's value. As arguments are places, these are always
 264 /// indirect.
 265 fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 266     bx: &mut Bx,
 267     fx: &mut FunctionCx<'a, 'tcx, Bx>,
 268     memory_locals: &BitSet<mir::Local>,
 269 ) -> Vec<LocalRef<'tcx, Bx::Value>> {
 270     let mir = fx.mir;
 271     let mut idx = 0;
 272     let mut llarg_idx = fx.fn_abi.ret.is_indirect() as usize;
 273
 274     let args = mir
 275         .args_iter()
 276         .enumerate()
 277         .map(|(arg_index, local)| {
 278             let arg_decl = &mir.local_decls[local];
 279
 280             if Some(local) == mir.spread_arg {
 281                 // This argument (e.g., the last argument in the "rust-call" ABI)
 282                 // is a tuple that was spread at the ABI level and now we have
 283                 // to reconstruct it into a tuple local variable, from multiple
 284                 // individual LLVM function arguments.
 285
 286                 let arg_ty = fx.monomorphize(arg_decl.ty);
 287                 let tupled_arg_tys = match arg_ty.kind() {
 288                     ty::Tuple(tys) => tys,
 289                     _ => bug!("spread argument isn't a tuple?!"),
 290                 };
 291
 292                 let place = PlaceRef::alloca(bx, bx.layout_of(arg_ty));
 293                 for i in 0..tupled_arg_tys.len() {
 294                     let arg = &fx.fn_abi.args[idx];
 295                     idx += 1;
 296                     if arg.pad.is_some() {
 297                         llarg_idx += 1;
 298                     }
 299                     let pr_field = place.project_field(bx, i);
 300                     bx.store_fn_arg(arg, &mut llarg_idx, pr_field);
 301                 }
 302
 303                 return LocalRef::Place(place);
 304             }
 305
 306             if fx.fn_abi.c_variadic && arg_index == fx.fn_abi.args.len() {
 307                 let arg_ty = fx.monomorphize(arg_decl.ty);
 308
 309                 let va_list = PlaceRef::alloca(bx, bx.layout_of(arg_ty));
 310                 bx.va_start(va_list.llval);
 311
 312                 return LocalRef::Place(va_list);
 313             }
 314
 315             let arg = &fx.fn_abi.args[idx];
 316             idx += 1;
 317             if arg.pad.is_some() {
 318                 llarg_idx += 1;
 319             }
 320
 321             if !memory_locals.contains(local) {
 322                 // We don't have to cast or keep the argument in the alloca.
 323                 // FIXME(eddyb): We should figure out how to use llvm.dbg.value instead
 324                 // of putting everything in allocas just so we can use llvm.dbg.declare.
 325                 let local = |op| LocalRef::Operand(Some(op));
 326                 match arg.mode {
 327                     PassMode::Ignore => {
 328                         return local(OperandRef::new_zst(bx, arg.layout));
 329                     }
 330                     PassMode::Direct(_) => {
 331                         let llarg = bx.get_param(llarg_idx);
 332                         llarg_idx += 1;
 333                         return local(OperandRef::from_immediate_or_packed_pair(
 334                             bx, llarg, arg.layout,
 335                         ));
 336                     }
 337                     PassMode::Pair(..) => {
 338                         let (a, b) = (bx.get_param(llarg_idx), bx.get_param(llarg_idx + 1));
 339                         llarg_idx += 2;
 340
 341                         return local(OperandRef {
 342                             val: OperandValue::Pair(a, b),
 343                             layout: arg.layout,
 344                         });
 345                     }
 346                     _ => {}
 347                 }
 348             }
 349
 350             if arg.is_sized_indirect() {
 351                 // Don't copy an indirect argument to an alloca, the caller
 352                 // already put it in a temporary alloca and gave it up.
 353                 // FIXME: lifetimes
 354                 let llarg = bx.get_param(llarg_idx);
 355                 llarg_idx += 1;
 356                 LocalRef::Place(PlaceRef::new_sized(llarg, arg.layout))
 357             } else if arg.is_unsized_indirect() {
 358                 // As the storage for the indirect argument lives during
 359                 // the whole function call, we just copy the fat pointer.
 360                 let llarg = bx.get_param(llarg_idx);
 361                 llarg_idx += 1;
 362                 let llextra = bx.get_param(llarg_idx);
 363                 llarg_idx += 1;
 364                 let indirect_operand = OperandValue::Pair(llarg, llextra);
 365
 366                 let tmp = PlaceRef::alloca_unsized_indirect(bx, arg.layout);
 367                 indirect_operand.store(bx, tmp);
 368                 LocalRef::UnsizedPlace(tmp)
 369             } else {
 370                 let tmp = PlaceRef::alloca(bx, arg.layout);
 371                 bx.store_fn_arg(arg, &mut llarg_idx, tmp);
 372                 LocalRef::Place(tmp)
 373             }
 374         })
 375         .collect::<Vec<_>>();
 376
 377     if fx.instance.def.requires_caller_location(bx.tcx()) {
 378         assert_eq!(
 379             fx.fn_abi.args.len(),
 380             args.len() + 1,
 381             "#[track_caller] fn's must have 1 more argument in their ABI than in their MIR",
 382         );
 383
 384         let arg = fx.fn_abi.args.last().unwrap();
 385         match arg.mode {
 386             PassMode::Direct(_) => (),
 387             _ => bug!("caller location must be PassMode::Direct, found {:?}", arg.mode),
 388         }
 389
 390         fx.caller_location = Some(OperandRef {
 391             val: OperandValue::Immediate(bx.get_param(llarg_idx)),
 392             layout: arg.layout,
 393         });
 394     }
 395
 396     args
 397 }
 398
 399 mod analyze;
 400 mod block;
 401 pub mod constant;
 402 pub mod coverageinfo;
 403 pub mod debuginfo;
 404 mod intrinsic;
 405 pub mod operand;
 406 pub mod place;
 407 mod rvalue;
 408 mod statement;