src/librustc_codegen_ssa/mir/mod.rs

   1 use crate::base;
   2 use crate::traits::*;
   3 use rustc_errors::ErrorReported;
   4 use rustc_middle::mir;
   5 use rustc_middle::mir::interpret::ErrorHandled;
   6 use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt, TyAndLayout};
   7 use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
   8 use rustc_target::abi::call::{FnAbi, PassMode};
   9 use rustc_target::abi::HasDataLayout;
  10
  11 use std::iter;
  12
  13 use rustc_index::bit_set::BitSet;
  14 use rustc_index::vec::IndexVec;
  15
  16 use self::analyze::CleanupKind;
  17 use self::debuginfo::{FunctionDebugContext, PerLocalVarDebugInfo};
  18 use self::place::PlaceRef;
  19 use rustc_middle::mir::traversal;
  20
  21 use self::operand::{OperandRef, OperandValue};
  22
  23 /// Master context for codegenning from MIR.
  24 pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
  25     instance: Instance<'tcx>,
  26
  27     mir: &'tcx mir::Body<'tcx>,
  28
  29     debug_context: Option<FunctionDebugContext<Bx::DIScope>>,
  30
  31     llfn: Bx::Function,
  32
  33     cx: &'a Bx::CodegenCx,
  34
  35     fn_abi: FnAbi<'tcx, Ty<'tcx>>,
  36
  37     /// When unwinding is initiated, we have to store this personality
  38     /// value somewhere so that we can load it and re-use it in the
  39     /// resume instruction. The personality is (afaik) some kind of
  40     /// value used for C++ unwinding, which must filter by type: we
  41     /// don't really care about it very much. Anyway, this value
  42     /// contains an alloca into which the personality is stored and
  43     /// then later loaded when generating the DIVERGE_BLOCK.
  44     personality_slot: Option<PlaceRef<'tcx, Bx::Value>>,
  45
  46     /// A `Block` for each MIR `BasicBlock`
  47     blocks: IndexVec<mir::BasicBlock, 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
  53     /// BB. This is initialized as we compute the funclets' head block in RPO.
  54     funclets: IndexVec<mir::BasicBlock, Option<Bx::Funclet>>,
  55
  56     /// This stores the landing-pad block for a given BB, computed lazily on GNU
  57     /// and eagerly on MSVC.
  58     landing_pads: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>>,
  59
  60     /// Cached unreachable block
  61     unreachable_block: Option<Bx::BasicBlock>,
  62
  63     /// The location where each MIR arg/var/tmp/ret is stored. This is
  64     /// usually an `PlaceRef` representing an alloca, but not always:
  65     /// sometimes we can skip the alloca and just store the value
  66     /// directly using an `OperandRef`, which makes for tighter LLVM
  67     /// IR. The conditions for using an `OperandRef` are as follows:
  68     ///
  69     /// - the type of the local must be judged "immediate" by `is_llvm_immediate`
  70     /// - the operand must never be referenced indirectly
  71     ///     - we should not take its address using the `&` operator
  72     ///     - nor should it appear in a place path like `tmp.a`
  73     /// - the operand must be defined by an rvalue that can generate immediate
  74     ///   values
  75     ///
  76     /// Avoiding allocs can also be important for certain intrinsics,
  77     /// notably `expect`.
  78     locals: IndexVec<mir::Local, LocalRef<'tcx, Bx::Value>>,
  79
  80     /// All `VarDebugInfo` from the MIR body, partitioned by `Local`.
  81     /// This is `None` if no var`#[non_exhaustive]`iable debuginfo/names are needed.
  82     per_local_var_debug_info:
  83         Option<IndexVec<mir::Local, Vec<PerLocalVarDebugInfo<'tcx, Bx::DIVariable>>>>,
  84
  85     /// Caller location propagated if this function has `#[track_caller]`.
  86     caller_location: Option<OperandRef<'tcx, Bx::Value>>,
  87 }
  88
  89 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  90     pub fn monomorphize<T>(&self, value: &T) -> T
  91     where
  92         T: Copy + TypeFoldable<'tcx>,
  93     {
  94         debug!("monomorphize: self.instance={:?}", self.instance);
  95         if let Some(substs) = self.instance.substs_for_mir_body() {
  96             self.cx.tcx().subst_and_normalize_erasing_regions(
  97                 substs,
  98                 ty::ParamEnv::reveal_all(),
  99                 &value,
 100             )
 101         } else {
 102             self.cx.tcx().normalize_erasing_regions(ty::ParamEnv::reveal_all(), *value)
 103         }
 104     }
 105 }
 106
 107 enum LocalRef<'tcx, V> {
 108     Place(PlaceRef<'tcx, V>),
 109     /// `UnsizedPlace(p)`: `p` itself is a thin pointer (indirect place).
 110     /// `*p` is the fat pointer that references the actual unsized place.
 111     /// Every time it is initialized, we have to reallocate the place
 112     /// and update the fat pointer. That's the reason why it is indirect.
 113     UnsizedPlace(PlaceRef<'tcx, V>),
 114     Operand(Option<OperandRef<'tcx, V>>),
 115 }
 116
 117 impl<'a, 'tcx, V: CodegenObject> LocalRef<'tcx, V> {
 118     fn new_operand<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 119         bx: &mut Bx,
 120         layout: TyAndLayout<'tcx>,
 121     ) -> LocalRef<'tcx, V> {
 122         if layout.is_zst() {
 123             // Zero-size temporaries aren't always initialized, which
 124             // doesn't matter because they don't contain data, but
 125             // we need something in the operand.
 126             LocalRef::Operand(Some(OperandRef::new_zst(bx, layout)))
 127         } else {
 128             LocalRef::Operand(None)
 129         }
 130     }
 131 }
 132
 133 ///////////////////////////////////////////////////////////////////////////
 134
 135 pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 136     cx: &'a Bx::CodegenCx,
 137     instance: Instance<'tcx>,
 138 ) {
 139     assert!(!instance.substs.needs_infer());
 140
 141     let llfn = cx.get_fn(instance);
 142
 143     let mir = cx.tcx().instance_mir(instance.def);
 144
 145     let fn_abi = FnAbi::of_instance(cx, instance, &[]);
 146     debug!("fn_abi: {:?}", fn_abi);
 147
 148     let debug_context = cx.create_function_debug_context(instance, &fn_abi, llfn, &mir);
 149
 150     let mut bx = Bx::new_block(cx, llfn, "start");
 151
 152     if mir.basic_blocks().iter().any(|bb| bb.is_cleanup) {
 153         bx.set_personality_fn(cx.eh_personality());
 154     }
 155
 156     bx.sideeffect();
 157
 158     let cleanup_kinds = analyze::cleanup_kinds(&mir);
 159     // Allocate a `Block` for every basic block, except
 160     // the start block, if nothing loops back to it.
 161     let reentrant_start_block = !mir.predecessors()[mir::START_BLOCK].is_empty();
 162     let block_bxs: IndexVec<mir::BasicBlock, Bx::BasicBlock> = mir
 163         .basic_blocks()
 164         .indices()
 165         .map(|bb| {
 166             if bb == mir::START_BLOCK && !reentrant_start_block {
 167                 bx.llbb()
 168             } else {
 169                 bx.build_sibling_block(&format!("{:?}", bb)).llbb()
 170             }
 171         })
 172         .collect();
 173
 174     let (landing_pads, funclets) = create_funclets(&mir, &mut bx, &cleanup_kinds, &block_bxs);
 175     let mut fx = FunctionCx {
 176         instance,
 177         mir,
 178         llfn,
 179         fn_abi,
 180         cx,
 181         personality_slot: None,
 182         blocks: block_bxs,
 183         unreachable_block: None,
 184         cleanup_kinds,
 185         landing_pads,
 186         funclets,
 187         locals: IndexVec::new(),
 188         debug_context,
 189         per_local_var_debug_info: None,
 190         caller_location: None,
 191     };
 192
 193     fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info();
 194
 195     for const_ in &mir.required_consts {
 196         if let Err(err) = fx.eval_mir_constant(const_) {
 197             match err {
 198                 // errored or at least linted
 199                 ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted => {}
 200                 ErrorHandled::TooGeneric => {
 201                     span_bug!(const_.span, "codgen encountered polymorphic constant: {:?}", err)
 202                 }
 203             }
 204         }
 205     }
 206
 207     let memory_locals = analyze::non_ssa_locals(&fx);
 208
 209     // Allocate variable and temp allocas
 210     fx.locals = {
 211         let args = arg_local_refs(&mut bx, &mut fx, &memory_locals);
 212
 213         let mut allocate_local = |local| {
 214             let decl = &mir.local_decls[local];
 215             let layout = bx.layout_of(fx.monomorphize(&decl.ty));
 216             assert!(!layout.ty.has_erasable_regions());
 217
 218             if local == mir::RETURN_PLACE && fx.fn_abi.ret.is_indirect() {
 219                 debug!("alloc: {:?} (return place) -> place", local);
 220                 let llretptr = bx.get_param(0);
 221                 return LocalRef::Place(PlaceRef::new_sized(llretptr, layout));
 222             }
 223
 224             if memory_locals.contains(local) {
 225                 debug!("alloc: {:?} -> place", local);
 226                 if layout.is_unsized() {
 227                     LocalRef::UnsizedPlace(PlaceRef::alloca_unsized_indirect(&mut bx, layout))
 228                 } else {
 229                     LocalRef::Place(PlaceRef::alloca(&mut bx, layout))
 230                 }
 231             } else {
 232                 debug!("alloc: {:?} -> operand", local);
 233                 LocalRef::new_operand(&mut bx, layout)
 234             }
 235         };
 236
 237         let retptr = allocate_local(mir::RETURN_PLACE);
 238         iter::once(retptr)
 239             .chain(args.into_iter())
 240             .chain(mir.vars_and_temps_iter().map(allocate_local))
 241             .collect()
 242     };
 243
 244     // Apply debuginfo to the newly allocated locals.
 245     fx.debug_introduce_locals(&mut bx);
 246
 247     // Branch to the START block, if it's not the entry block.
 248     if reentrant_start_block {
 249         bx.br(fx.blocks[mir::START_BLOCK]);
 250     }
 251
 252     let rpo = traversal::reverse_postorder(&mir);
 253     let mut visited = BitSet::new_empty(mir.basic_blocks().len());
 254
 255     // Codegen the body of each block using reverse postorder
 256     for (bb, _) in rpo {
 257         visited.insert(bb.index());
 258         fx.codegen_block(bb);
 259     }
 260
 261     // Remove blocks that haven't been visited, or have no
 262     // predecessors.
 263     for bb in mir.basic_blocks().indices() {
 264         // Unreachable block
 265         if !visited.contains(bb.index()) {
 266             debug!("codegen_mir: block {:?} was not visited", bb);
 267             unsafe {
 268                 bx.delete_basic_block(fx.blocks[bb]);
 269             }
 270         }
 271     }
 272 }
 273
 274 fn create_funclets<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 275     mir: &'tcx mir::Body<'tcx>,
 276     bx: &mut Bx,
 277     cleanup_kinds: &IndexVec<mir::BasicBlock, CleanupKind>,
 278     block_bxs: &IndexVec<mir::BasicBlock, Bx::BasicBlock>,
 279 ) -> (
 280     IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>>,
 281     IndexVec<mir::BasicBlock, Option<Bx::Funclet>>,
 282 ) {
 283     block_bxs
 284         .iter_enumerated()
 285         .zip(cleanup_kinds)
 286         .map(|((bb, &llbb), cleanup_kind)| {
 287             match *cleanup_kind {
 288                 CleanupKind::Funclet if base::wants_msvc_seh(bx.sess()) => {}
 289                 _ => return (None, None),
 290             }
 291
 292             let funclet;
 293             let ret_llbb;
 294             match mir[bb].terminator.as_ref().map(|t| &t.kind) {
 295                 // This is a basic block that we're aborting the program for,
 296                 // notably in an `extern` function. These basic blocks are inserted
 297                 // so that we assert that `extern` functions do indeed not panic,
 298                 // and if they do we abort the process.
 299                 //
 300                 // On MSVC these are tricky though (where we're doing funclets). If
 301                 // we were to do a cleanuppad (like below) the normal functions like
 302                 // `longjmp` would trigger the abort logic, terminating the
 303                 // program. Instead we insert the equivalent of `catch(...)` for C++
 304                 // which magically doesn't trigger when `longjmp` files over this
 305                 // frame.
 306                 //
 307                 // Lots more discussion can be found on #48251 but this codegen is
 308                 // modeled after clang's for:
 309                 //
 310                 //      try {
 311                 //          foo();
 312                 //      } catch (...) {
 313                 //          bar();
 314                 //      }
 315                 Some(&mir::TerminatorKind::Abort) => {
 316                     let mut cs_bx = bx.build_sibling_block(&format!("cs_funclet{:?}", bb));
 317                     let mut cp_bx = bx.build_sibling_block(&format!("cp_funclet{:?}", bb));
 318                     ret_llbb = cs_bx.llbb();
 319
 320                     let cs = cs_bx.catch_switch(None, None, 1);
 321                     cs_bx.add_handler(cs, cp_bx.llbb());
 322
 323                     // The "null" here is actually a RTTI type descriptor for the
 324                     // C++ personality function, but `catch (...)` has no type so
 325                     // it's null. The 64 here is actually a bitfield which
 326                     // represents that this is a catch-all block.
 327                     let null = bx.const_null(
 328                         bx.type_i8p_ext(bx.cx().data_layout().instruction_address_space),
 329                     );
 330                     let sixty_four = bx.const_i32(64);
 331                     funclet = cp_bx.catch_pad(cs, &[null, sixty_four, null]);
 332                     cp_bx.br(llbb);
 333                 }
 334                 _ => {
 335                     let mut cleanup_bx = bx.build_sibling_block(&format!("funclet_{:?}", bb));
 336                     ret_llbb = cleanup_bx.llbb();
 337                     funclet = cleanup_bx.cleanup_pad(None, &[]);
 338                     cleanup_bx.br(llbb);
 339                 }
 340             };
 341
 342             (Some(ret_llbb), Some(funclet))
 343         })
 344         .unzip()
 345 }
 346
 347 /// Produces, for each argument, a `Value` pointing at the
 348 /// argument's value. As arguments are places, these are always
 349 /// indirect.
 350 fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 351     bx: &mut Bx,
 352     fx: &mut FunctionCx<'a, 'tcx, Bx>,
 353     memory_locals: &BitSet<mir::Local>,
 354 ) -> Vec<LocalRef<'tcx, Bx::Value>> {
 355     let mir = fx.mir;
 356     let mut idx = 0;
 357     let mut llarg_idx = fx.fn_abi.ret.is_indirect() as usize;
 358
 359     let args = mir
 360         .args_iter()
 361         .enumerate()
 362         .map(|(arg_index, local)| {
 363             let arg_decl = &mir.local_decls[local];
 364
 365             if Some(local) == mir.spread_arg {
 366                 // This argument (e.g., the last argument in the "rust-call" ABI)
 367                 // is a tuple that was spread at the ABI level and now we have
 368                 // to reconstruct it into a tuple local variable, from multiple
 369                 // individual LLVM function arguments.
 370
 371                 let arg_ty = fx.monomorphize(&arg_decl.ty);
 372                 let tupled_arg_tys = match arg_ty.kind {
 373                     ty::Tuple(ref tys) => tys,
 374                     _ => bug!("spread argument isn't a tuple?!"),
 375                 };
 376
 377                 let place = PlaceRef::alloca(bx, bx.layout_of(arg_ty));
 378                 for i in 0..tupled_arg_tys.len() {
 379                     let arg = &fx.fn_abi.args[idx];
 380                     idx += 1;
 381                     if arg.pad.is_some() {
 382                         llarg_idx += 1;
 383                     }
 384                     let pr_field = place.project_field(bx, i);
 385                     bx.store_fn_arg(arg, &mut llarg_idx, pr_field);
 386                 }
 387
 388                 return LocalRef::Place(place);
 389             }
 390
 391             if fx.fn_abi.c_variadic && arg_index == fx.fn_abi.args.len() {
 392                 let arg_ty = fx.monomorphize(&arg_decl.ty);
 393
 394                 let va_list = PlaceRef::alloca(bx, bx.layout_of(arg_ty));
 395                 bx.va_start(va_list.llval);
 396
 397                 return LocalRef::Place(va_list);
 398             }
 399
 400             let arg = &fx.fn_abi.args[idx];
 401             idx += 1;
 402             if arg.pad.is_some() {
 403                 llarg_idx += 1;
 404             }
 405
 406             if !memory_locals.contains(local) {
 407                 // We don't have to cast or keep the argument in the alloca.
 408                 // FIXME(eddyb): We should figure out how to use llvm.dbg.value instead
 409                 // of putting everything in allocas just so we can use llvm.dbg.declare.
 410                 let local = |op| LocalRef::Operand(Some(op));
 411                 match arg.mode {
 412                     PassMode::Ignore => {
 413                         return local(OperandRef::new_zst(bx, arg.layout));
 414                     }
 415                     PassMode::Direct(_) => {
 416                         let llarg = bx.get_param(llarg_idx);
 417                         llarg_idx += 1;
 418                         return local(OperandRef::from_immediate_or_packed_pair(
 419                             bx, llarg, arg.layout,
 420                         ));
 421                     }
 422                     PassMode::Pair(..) => {
 423                         let (a, b) = (bx.get_param(llarg_idx), bx.get_param(llarg_idx + 1));
 424                         llarg_idx += 2;
 425
 426                         return local(OperandRef {
 427                             val: OperandValue::Pair(a, b),
 428                             layout: arg.layout,
 429                         });
 430                     }
 431                     _ => {}
 432                 }
 433             }
 434
 435             if arg.is_sized_indirect() {
 436                 // Don't copy an indirect argument to an alloca, the caller
 437                 // already put it in a temporary alloca and gave it up.
 438                 // FIXME: lifetimes
 439                 let llarg = bx.get_param(llarg_idx);
 440                 llarg_idx += 1;
 441                 LocalRef::Place(PlaceRef::new_sized(llarg, arg.layout))
 442             } else if arg.is_unsized_indirect() {
 443                 // As the storage for the indirect argument lives during
 444                 // the whole function call, we just copy the fat pointer.
 445                 let llarg = bx.get_param(llarg_idx);
 446                 llarg_idx += 1;
 447                 let llextra = bx.get_param(llarg_idx);
 448                 llarg_idx += 1;
 449                 let indirect_operand = OperandValue::Pair(llarg, llextra);
 450
 451                 let tmp = PlaceRef::alloca_unsized_indirect(bx, arg.layout);
 452                 indirect_operand.store(bx, tmp);
 453                 LocalRef::UnsizedPlace(tmp)
 454             } else {
 455                 let tmp = PlaceRef::alloca(bx, arg.layout);
 456                 bx.store_fn_arg(arg, &mut llarg_idx, tmp);
 457                 LocalRef::Place(tmp)
 458             }
 459         })
 460         .collect::<Vec<_>>();
 461
 462     if fx.instance.def.requires_caller_location(bx.tcx()) {
 463         assert_eq!(
 464             fx.fn_abi.args.len(),
 465             args.len() + 1,
 466             "#[track_caller] fn's must have 1 more argument in their ABI than in their MIR",
 467         );
 468
 469         let arg = fx.fn_abi.args.last().unwrap();
 470         match arg.mode {
 471             PassMode::Direct(_) => (),
 472             _ => bug!("caller location must be PassMode::Direct, found {:?}", arg.mode),
 473         }
 474
 475         fx.caller_location = Some(OperandRef {
 476             val: OperandValue::Immediate(bx.get_param(llarg_idx)),
 477             layout: arg.layout,
 478         });
 479     }
 480
 481     args
 482 }
 483
 484 mod analyze;
 485 mod block;
 486 pub mod constant;
 487 pub mod coverageinfo;
 488 pub mod debuginfo;
 489 pub mod operand;
 490 pub mod place;
 491 mod rvalue;
 492 mod statement;