src/librustc_trans/mir/mod.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 common::{C_i32, C_null};
  12 use libc::c_uint;
  13 use llvm::{self, ValueRef, BasicBlockRef};
  14 use llvm::debuginfo::DIScope;
  15 use rustc::ty::{self, TypeFoldable};
  16 use rustc::ty::layout::{LayoutOf, TyLayout};
  17 use rustc::mir::{self, Mir};
  18 use rustc::ty::subst::Substs;
  19 use rustc::session::config::FullDebugInfo;
  20 use base;
  21 use builder::Builder;
  22 use common::{CodegenCx, Funclet};
  23 use debuginfo::{self, declare_local, VariableAccess, VariableKind, FunctionDebugContext};
  24 use monomorphize::Instance;
  25 use abi::{ArgAttribute, FnType, PassMode};
  26 use type_::Type;
  27
  28 use syntax_pos::{DUMMY_SP, NO_EXPANSION, BytePos, Span};
  29 use syntax::symbol::keywords;
  30
  31 use std::iter;
  32
  33 use rustc_data_structures::bitvec::BitVector;
  34 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
  35
  36 pub use self::constant::trans_static_initializer;
  37
  38 use self::analyze::CleanupKind;
  39 use self::place::PlaceRef;
  40 use rustc::mir::traversal;
  41
  42 use self::operand::{OperandRef, OperandValue};
  43
  44 /// Master context for translating MIR.
  45 pub struct FunctionCx<'a, 'tcx:'a> {
  46     instance: Instance<'tcx>,
  47
  48     mir: &'a mir::Mir<'tcx>,
  49
  50     debug_context: debuginfo::FunctionDebugContext,
  51
  52     llfn: ValueRef,
  53
  54     cx: &'a CodegenCx<'a, 'tcx>,
  55
  56     fn_ty: FnType<'tcx>,
  57
  58     /// When unwinding is initiated, we have to store this personality
  59     /// value somewhere so that we can load it and re-use it in the
  60     /// resume instruction. The personality is (afaik) some kind of
  61     /// value used for C++ unwinding, which must filter by type: we
  62     /// don't really care about it very much. Anyway, this value
  63     /// contains an alloca into which the personality is stored and
  64     /// then later loaded when generating the DIVERGE_BLOCK.
  65     personality_slot: Option<PlaceRef<'tcx>>,
  66
  67     /// A `Block` for each MIR `BasicBlock`
  68     blocks: IndexVec<mir::BasicBlock, BasicBlockRef>,
  69
  70     /// The funclet status of each basic block
  71     cleanup_kinds: IndexVec<mir::BasicBlock, analyze::CleanupKind>,
  72
  73     /// When targeting MSVC, this stores the cleanup info for each funclet
  74     /// BB. This is initialized as we compute the funclets' head block in RPO.
  75     funclets: &'a IndexVec<mir::BasicBlock, Option<Funclet>>,
  76
  77     /// This stores the landing-pad block for a given BB, computed lazily on GNU
  78     /// and eagerly on MSVC.
  79     landing_pads: IndexVec<mir::BasicBlock, Option<BasicBlockRef>>,
  80
  81     /// Cached unreachable block
  82     unreachable_block: Option<BasicBlockRef>,
  83
  84     /// The location where each MIR arg/var/tmp/ret is stored. This is
  85     /// usually an `PlaceRef` representing an alloca, but not always:
  86     /// sometimes we can skip the alloca and just store the value
  87     /// directly using an `OperandRef`, which makes for tighter LLVM
  88     /// IR. The conditions for using an `OperandRef` are as follows:
  89     ///
  90     /// - the type of the local must be judged "immediate" by `is_llvm_immediate`
  91     /// - the operand must never be referenced indirectly
  92     ///     - we should not take its address using the `&` operator
  93     ///     - nor should it appear in a place path like `tmp.a`
  94     /// - the operand must be defined by an rvalue that can generate immediate
  95     ///   values
  96     ///
  97     /// Avoiding allocs can also be important for certain intrinsics,
  98     /// notably `expect`.
  99     locals: IndexVec<mir::Local, LocalRef<'tcx>>,
 100
 101     /// Debug information for MIR scopes.
 102     scopes: IndexVec<mir::VisibilityScope, debuginfo::MirDebugScope>,
 103
 104     /// If this function is being monomorphized, this contains the type substitutions used.
 105     param_substs: &'tcx Substs<'tcx>,
 106 }
 107
 108 impl<'a, 'tcx> FunctionCx<'a, 'tcx> {
 109     pub fn monomorphize<T>(&self, value: &T) -> T
 110         where T: TypeFoldable<'tcx>
 111     {
 112         self.cx.tcx.subst_and_normalize_erasing_regions(
 113             self.param_substs,
 114             ty::ParamEnv::reveal_all(),
 115             value,
 116         )
 117     }
 118
 119     pub fn set_debug_loc(&mut self, bx: &Builder, source_info: mir::SourceInfo) {
 120         let (scope, span) = self.debug_loc(source_info);
 121         debuginfo::set_source_location(&self.debug_context, bx, scope, span);
 122     }
 123
 124     pub fn debug_loc(&mut self, source_info: mir::SourceInfo) -> (DIScope, Span) {
 125         // Bail out if debug info emission is not enabled.
 126         match self.debug_context {
 127             FunctionDebugContext::DebugInfoDisabled |
 128             FunctionDebugContext::FunctionWithoutDebugInfo => {
 129                 return (self.scopes[source_info.scope].scope_metadata, source_info.span);
 130             }
 131             FunctionDebugContext::RegularContext(_) =>{}
 132         }
 133
 134         // In order to have a good line stepping behavior in debugger, we overwrite debug
 135         // locations of macro expansions with that of the outermost expansion site
 136         // (unless the crate is being compiled with `-Z debug-macros`).
 137         if source_info.span.ctxt() == NO_EXPANSION ||
 138            self.cx.sess().opts.debugging_opts.debug_macros {
 139             let scope = self.scope_metadata_for_loc(source_info.scope, source_info.span.lo());
 140             (scope, source_info.span)
 141         } else {
 142             // Walk up the macro expansion chain until we reach a non-expanded span.
 143             // We also stop at the function body level because no line stepping can occur
 144             // at the level above that.
 145             let mut span = source_info.span;
 146             while span.ctxt() != NO_EXPANSION && span.ctxt() != self.mir.span.ctxt() {
 147                 if let Some(info) = span.ctxt().outer().expn_info() {
 148                     span = info.call_site;
 149                 } else {
 150                     break;
 151                 }
 152             }
 153             let scope = self.scope_metadata_for_loc(source_info.scope, span.lo());
 154             // Use span of the outermost expansion site, while keeping the original lexical scope.
 155             (scope, span)
 156         }
 157     }
 158
 159     // DILocations inherit source file name from the parent DIScope.  Due to macro expansions
 160     // it may so happen that the current span belongs to a different file than the DIScope
 161     // corresponding to span's containing visibility scope.  If so, we need to create a DIScope
 162     // "extension" into that file.
 163     fn scope_metadata_for_loc(&self, scope_id: mir::VisibilityScope, pos: BytePos)
 164                                -> llvm::debuginfo::DIScope {
 165         let scope_metadata = self.scopes[scope_id].scope_metadata;
 166         if pos < self.scopes[scope_id].file_start_pos ||
 167            pos >= self.scopes[scope_id].file_end_pos {
 168             let cm = self.cx.sess().codemap();
 169             let defining_crate = self.debug_context.get_ref(DUMMY_SP).defining_crate;
 170             debuginfo::extend_scope_to_file(self.cx,
 171                                             scope_metadata,
 172                                             &cm.lookup_char_pos(pos).file,
 173                                             defining_crate)
 174         } else {
 175             scope_metadata
 176         }
 177     }
 178 }
 179
 180 enum LocalRef<'tcx> {
 181     Place(PlaceRef<'tcx>),
 182     Operand(Option<OperandRef<'tcx>>),
 183 }
 184
 185 impl<'a, 'tcx> LocalRef<'tcx> {
 186     fn new_operand(cx: &CodegenCx<'a, 'tcx>, layout: TyLayout<'tcx>) -> LocalRef<'tcx> {
 187         if layout.is_zst() {
 188             // Zero-size temporaries aren't always initialized, which
 189             // doesn't matter because they don't contain data, but
 190             // we need something in the operand.
 191             LocalRef::Operand(Some(OperandRef::new_zst(cx, layout)))
 192         } else {
 193             LocalRef::Operand(None)
 194         }
 195     }
 196 }
 197
 198 ///////////////////////////////////////////////////////////////////////////
 199
 200 pub fn trans_mir<'a, 'tcx: 'a>(
 201     cx: &'a CodegenCx<'a, 'tcx>,
 202     llfn: ValueRef,
 203     mir: &'a Mir<'tcx>,
 204     instance: Instance<'tcx>,
 205     sig: ty::FnSig<'tcx>,
 206 ) {
 207     let fn_ty = FnType::new(cx, sig, &[]);
 208     debug!("fn_ty: {:?}", fn_ty);
 209     let debug_context =
 210         debuginfo::create_function_debug_context(cx, instance, sig, llfn, mir);
 211     let bx = Builder::new_block(cx, llfn, "start");
 212
 213     if mir.basic_blocks().iter().any(|bb| bb.is_cleanup) {
 214         bx.set_personality_fn(cx.eh_personality());
 215     }
 216
 217     let cleanup_kinds = analyze::cleanup_kinds(&mir);
 218     // Allocate a `Block` for every basic block, except
 219     // the start block, if nothing loops back to it.
 220     let reentrant_start_block = !mir.predecessors_for(mir::START_BLOCK).is_empty();
 221     let block_bxs: IndexVec<mir::BasicBlock, BasicBlockRef> =
 222         mir.basic_blocks().indices().map(|bb| {
 223             if bb == mir::START_BLOCK && !reentrant_start_block {
 224                 bx.llbb()
 225             } else {
 226                 bx.build_sibling_block(&format!("{:?}", bb)).llbb()
 227             }
 228         }).collect();
 229
 230     // Compute debuginfo scopes from MIR scopes.
 231     let scopes = debuginfo::create_mir_scopes(cx, mir, &debug_context);
 232     let (landing_pads, funclets) = create_funclets(mir, &bx, &cleanup_kinds, &block_bxs);
 233
 234     let mut fx = FunctionCx {
 235         instance,
 236         mir,
 237         llfn,
 238         fn_ty,
 239         cx,
 240         personality_slot: None,
 241         blocks: block_bxs,
 242         unreachable_block: None,
 243         cleanup_kinds,
 244         landing_pads,
 245         funclets: &funclets,
 246         scopes,
 247         locals: IndexVec::new(),
 248         debug_context,
 249         param_substs: {
 250             assert!(!instance.substs.needs_infer());
 251             instance.substs
 252         },
 253     };
 254
 255     let memory_locals = analyze::memory_locals(&fx);
 256
 257     // Allocate variable and temp allocas
 258     fx.locals = {
 259         let args = arg_local_refs(&bx, &fx, &fx.scopes, &memory_locals);
 260
 261         let mut allocate_local = |local| {
 262             let decl = &mir.local_decls[local];
 263             let layout = bx.cx.layout_of(fx.monomorphize(&decl.ty));
 264             assert!(!layout.ty.has_erasable_regions());
 265
 266             if let Some(name) = decl.name {
 267                 // User variable
 268                 let debug_scope = fx.scopes[decl.source_info.scope];
 269                 let dbg = debug_scope.is_valid() && bx.sess().opts.debuginfo == FullDebugInfo;
 270
 271                 if !memory_locals.contains(local.index()) && !dbg {
 272                     debug!("alloc: {:?} ({}) -> operand", local, name);
 273                     return LocalRef::new_operand(bx.cx, layout);
 274                 }
 275
 276                 debug!("alloc: {:?} ({}) -> place", local, name);
 277                 let place = PlaceRef::alloca(&bx, layout, &name.as_str());
 278                 if dbg {
 279                     let (scope, span) = fx.debug_loc(decl.source_info);
 280                     declare_local(&bx, &fx.debug_context, name, layout.ty, scope,
 281                         VariableAccess::DirectVariable { alloca: place.llval },
 282                         VariableKind::LocalVariable, span);
 283                 }
 284                 LocalRef::Place(place)
 285             } else {
 286                 // Temporary or return place
 287                 if local == mir::RETURN_PLACE && fx.fn_ty.ret.is_indirect() {
 288                     debug!("alloc: {:?} (return place) -> place", local);
 289                     let llretptr = llvm::get_param(llfn, 0);
 290                     LocalRef::Place(PlaceRef::new_sized(llretptr, layout, layout.align))
 291                 } else if memory_locals.contains(local.index()) {
 292                     debug!("alloc: {:?} -> place", local);
 293                     LocalRef::Place(PlaceRef::alloca(&bx, layout, &format!("{:?}", local)))
 294                 } else {
 295                     // If this is an immediate local, we do not create an
 296                     // alloca in advance. Instead we wait until we see the
 297                     // definition and update the operand there.
 298                     debug!("alloc: {:?} -> operand", local);
 299                     LocalRef::new_operand(bx.cx, layout)
 300                 }
 301             }
 302         };
 303
 304         let retptr = allocate_local(mir::RETURN_PLACE);
 305         iter::once(retptr)
 306             .chain(args.into_iter())
 307             .chain(mir.vars_and_temps_iter().map(allocate_local))
 308             .collect()
 309     };
 310
 311     // Branch to the START block, if it's not the entry block.
 312     if reentrant_start_block {
 313         bx.br(fx.blocks[mir::START_BLOCK]);
 314     }
 315
 316     // Up until here, IR instructions for this function have explicitly not been annotated with
 317     // source code location, so we don't step into call setup code. From here on, source location
 318     // emitting should be enabled.
 319     debuginfo::start_emitting_source_locations(&fx.debug_context);
 320
 321     let rpo = traversal::reverse_postorder(&mir);
 322     let mut visited = BitVector::new(mir.basic_blocks().len());
 323
 324     // Translate the body of each block using reverse postorder
 325     for (bb, _) in rpo {
 326         visited.insert(bb.index());
 327         fx.trans_block(bb);
 328     }
 329
 330     // Remove blocks that haven't been visited, or have no
 331     // predecessors.
 332     for bb in mir.basic_blocks().indices() {
 333         // Unreachable block
 334         if !visited.contains(bb.index()) {
 335             debug!("trans_mir: block {:?} was not visited", bb);
 336             unsafe {
 337                 llvm::LLVMDeleteBasicBlock(fx.blocks[bb]);
 338             }
 339         }
 340     }
 341 }
 342
 343 fn create_funclets<'a, 'tcx>(
 344     mir: &'a Mir<'tcx>,
 345     bx: &Builder<'a, 'tcx>,
 346     cleanup_kinds: &IndexVec<mir::BasicBlock, CleanupKind>,
 347     block_bxs: &IndexVec<mir::BasicBlock, BasicBlockRef>)
 348     -> (IndexVec<mir::BasicBlock, Option<BasicBlockRef>>,
 349         IndexVec<mir::BasicBlock, Option<Funclet>>)
 350 {
 351     block_bxs.iter_enumerated().zip(cleanup_kinds).map(|((bb, &llbb), cleanup_kind)| {
 352         match *cleanup_kind {
 353             CleanupKind::Funclet if base::wants_msvc_seh(bx.sess()) => {}
 354             _ => return (None, None)
 355         }
 356
 357         let cleanup;
 358         let ret_llbb;
 359         match mir[bb].terminator.as_ref().map(|t| &t.kind) {
 360             // This is a basic block that we're aborting the program for,
 361             // notably in an `extern` function. These basic blocks are inserted
 362             // so that we assert that `extern` functions do indeed not panic,
 363             // and if they do we abort the process.
 364             //
 365             // On MSVC these are tricky though (where we're doing funclets). If
 366             // we were to do a cleanuppad (like below) the normal functions like
 367             // `longjmp` would trigger the abort logic, terminating the
 368             // program. Instead we insert the equivalent of `catch(...)` for C++
 369             // which magically doesn't trigger when `longjmp` files over this
 370             // frame.
 371             //
 372             // Lots more discussion can be found on #48251 but this codegen is
 373             // modeled after clang's for:
 374             //
 375             //      try {
 376             //          foo();
 377             //      } catch (...) {
 378             //          bar();
 379             //      }
 380             Some(&mir::TerminatorKind::Abort) => {
 381                 let cs_bx = bx.build_sibling_block(&format!("cs_funclet{:?}", bb));
 382                 let cp_bx = bx.build_sibling_block(&format!("cp_funclet{:?}", bb));
 383                 ret_llbb = cs_bx.llbb();
 384
 385                 let cs = cs_bx.catch_switch(None, None, 1);
 386                 cs_bx.add_handler(cs, cp_bx.llbb());
 387
 388                 // The "null" here is actually a RTTI type descriptor for the
 389                 // C++ personality function, but `catch (...)` has no type so
 390                 // it's null. The 64 here is actually a bitfield which
 391                 // represents that this is a catch-all block.
 392                 let null = C_null(Type::i8p(bx.cx));
 393                 let sixty_four = C_i32(bx.cx, 64);
 394                 cleanup = cp_bx.catch_pad(cs, &[null, sixty_four, null]);
 395                 cp_bx.br(llbb);
 396             }
 397             _ => {
 398                 let cleanup_bx = bx.build_sibling_block(&format!("funclet_{:?}", bb));
 399                 ret_llbb = cleanup_bx.llbb();
 400                 cleanup = cleanup_bx.cleanup_pad(None, &[]);
 401                 cleanup_bx.br(llbb);
 402             }
 403         };
 404
 405         (Some(ret_llbb), Some(Funclet::new(cleanup)))
 406     }).unzip()
 407 }
 408
 409 /// Produce, for each argument, a `ValueRef` pointing at the
 410 /// argument's value. As arguments are places, these are always
 411 /// indirect.
 412 fn arg_local_refs<'a, 'tcx>(bx: &Builder<'a, 'tcx>,
 413                             fx: &FunctionCx<'a, 'tcx>,
 414                             scopes: &IndexVec<mir::VisibilityScope, debuginfo::MirDebugScope>,
 415                             memory_locals: &BitVector)
 416                             -> Vec<LocalRef<'tcx>> {
 417     let mir = fx.mir;
 418     let tcx = bx.tcx();
 419     let mut idx = 0;
 420     let mut llarg_idx = fx.fn_ty.ret.is_indirect() as usize;
 421
 422     // Get the argument scope, if it exists and if we need it.
 423     let arg_scope = scopes[mir::ARGUMENT_VISIBILITY_SCOPE];
 424     let arg_scope = if arg_scope.is_valid() && bx.sess().opts.debuginfo == FullDebugInfo {
 425         Some(arg_scope.scope_metadata)
 426     } else {
 427         None
 428     };
 429
 430     let deref_op = unsafe {
 431         [llvm::LLVMRustDIBuilderCreateOpDeref()]
 432     };
 433
 434     mir.args_iter().enumerate().map(|(arg_index, local)| {
 435         let arg_decl = &mir.local_decls[local];
 436
 437         let name = if let Some(name) = arg_decl.name {
 438             name.as_str().to_string()
 439         } else {
 440             format!("arg{}", arg_index)
 441         };
 442
 443         if Some(local) == mir.spread_arg {
 444             // This argument (e.g. the last argument in the "rust-call" ABI)
 445             // is a tuple that was spread at the ABI level and now we have
 446             // to reconstruct it into a tuple local variable, from multiple
 447             // individual LLVM function arguments.
 448
 449             let arg_ty = fx.monomorphize(&arg_decl.ty);
 450             let tupled_arg_tys = match arg_ty.sty {
 451                 ty::TyTuple(ref tys) => tys,
 452                 _ => bug!("spread argument isn't a tuple?!")
 453             };
 454
 455             let place = PlaceRef::alloca(bx, bx.cx.layout_of(arg_ty), &name);
 456             for i in 0..tupled_arg_tys.len() {
 457                 let arg = &fx.fn_ty.args[idx];
 458                 idx += 1;
 459                 if arg.pad.is_some() {
 460                     llarg_idx += 1;
 461                 }
 462                 arg.store_fn_arg(bx, &mut llarg_idx, place.project_field(bx, i));
 463             }
 464
 465             // Now that we have one alloca that contains the aggregate value,
 466             // we can create one debuginfo entry for the argument.
 467             arg_scope.map(|scope| {
 468                 let variable_access = VariableAccess::DirectVariable {
 469                     alloca: place.llval
 470                 };
 471                 declare_local(
 472                     bx,
 473                     &fx.debug_context,
 474                     arg_decl.name.unwrap_or(keywords::Invalid.name()),
 475                     arg_ty, scope,
 476                     variable_access,
 477                     VariableKind::ArgumentVariable(arg_index + 1),
 478                     DUMMY_SP
 479                 );
 480             });
 481
 482             return LocalRef::Place(place);
 483         }
 484
 485         let arg = &fx.fn_ty.args[idx];
 486         idx += 1;
 487         if arg.pad.is_some() {
 488             llarg_idx += 1;
 489         }
 490
 491         if arg_scope.is_none() && !memory_locals.contains(local.index()) {
 492             // We don't have to cast or keep the argument in the alloca.
 493             // FIXME(eddyb): We should figure out how to use llvm.dbg.value instead
 494             // of putting everything in allocas just so we can use llvm.dbg.declare.
 495             let local = |op| LocalRef::Operand(Some(op));
 496             match arg.mode {
 497                 PassMode::Ignore => {
 498                     return local(OperandRef::new_zst(bx.cx, arg.layout));
 499                 }
 500                 PassMode::Direct(_) => {
 501                     let llarg = llvm::get_param(bx.llfn(), llarg_idx as c_uint);
 502                     bx.set_value_name(llarg, &name);
 503                     llarg_idx += 1;
 504                     return local(
 505                         OperandRef::from_immediate_or_packed_pair(bx, llarg, arg.layout));
 506                 }
 507                 PassMode::Pair(..) => {
 508                     let a = llvm::get_param(bx.llfn(), llarg_idx as c_uint);
 509                     bx.set_value_name(a, &(name.clone() + ".0"));
 510                     llarg_idx += 1;
 511
 512                     let b = llvm::get_param(bx.llfn(), llarg_idx as c_uint);
 513                     bx.set_value_name(b, &(name + ".1"));
 514                     llarg_idx += 1;
 515
 516                     return local(OperandRef {
 517                         val: OperandValue::Pair(a, b),
 518                         layout: arg.layout
 519                     });
 520                 }
 521                 _ => {}
 522             }
 523         }
 524
 525         let place = if arg.is_indirect() {
 526             // Don't copy an indirect argument to an alloca, the caller
 527             // already put it in a temporary alloca and gave it up.
 528             // FIXME: lifetimes
 529             let llarg = llvm::get_param(bx.llfn(), llarg_idx as c_uint);
 530             bx.set_value_name(llarg, &name);
 531             llarg_idx += 1;
 532             PlaceRef::new_sized(llarg, arg.layout, arg.layout.align)
 533         } else {
 534             let tmp = PlaceRef::alloca(bx, arg.layout, &name);
 535             arg.store_fn_arg(bx, &mut llarg_idx, tmp);
 536             tmp
 537         };
 538         arg_scope.map(|scope| {
 539             // Is this a regular argument?
 540             if arg_index > 0 || mir.upvar_decls.is_empty() {
 541                 // The Rust ABI passes indirect variables using a pointer and a manual copy, so we
 542                 // need to insert a deref here, but the C ABI uses a pointer and a copy using the
 543                 // byval attribute, for which LLVM does the deref itself, so we must not add it.
 544                 // Starting with D31439 in LLVM 5, it *always* does the deref itself.
 545                 let mut variable_access = VariableAccess::DirectVariable {
 546                     alloca: place.llval
 547                 };
 548                 if unsafe { llvm::LLVMRustVersionMajor() < 5 } {
 549                     if let PassMode::Indirect(ref attrs) = arg.mode {
 550                         if !attrs.contains(ArgAttribute::ByVal) {
 551                             variable_access = VariableAccess::IndirectVariable {
 552                                 alloca: place.llval,
 553                                 address_operations: &deref_op,
 554                             };
 555                         }
 556                     }
 557                 }
 558
 559                 declare_local(
 560                     bx,
 561                     &fx.debug_context,
 562                     arg_decl.name.unwrap_or(keywords::Invalid.name()),
 563                     arg.layout.ty,
 564                     scope,
 565                     variable_access,
 566                     VariableKind::ArgumentVariable(arg_index + 1),
 567                     DUMMY_SP
 568                 );
 569                 return;
 570             }
 571
 572             // Or is it the closure environment?
 573             let (closure_layout, env_ref) = match arg.layout.ty.sty {
 574                 ty::TyRef(_, mt) | ty::TyRawPtr(mt) => (bx.cx.layout_of(mt.ty), true),
 575                 _ => (arg.layout, false)
 576             };
 577
 578             let upvar_tys = match closure_layout.ty.sty {
 579                 ty::TyClosure(def_id, substs) |
 580                 ty::TyGenerator(def_id, substs, _) => substs.upvar_tys(def_id, tcx),
 581                 _ => bug!("upvar_decls with non-closure arg0 type `{}`", closure_layout.ty)
 582             };
 583
 584             // Store the pointer to closure data in an alloca for debuginfo
 585             // because that's what the llvm.dbg.declare intrinsic expects.
 586
 587             // FIXME(eddyb) this shouldn't be necessary but SROA seems to
 588             // mishandle DW_OP_plus not preceded by DW_OP_deref, i.e. it
 589             // doesn't actually strip the offset when splitting the closure
 590             // environment into its components so it ends up out of bounds.
 591             let env_ptr = if !env_ref {
 592                 let scratch = PlaceRef::alloca(bx,
 593                     bx.cx.layout_of(tcx.mk_mut_ptr(arg.layout.ty)),
 594                     "__debuginfo_env_ptr");
 595                 bx.store(place.llval, scratch.llval, scratch.align);
 596                 scratch.llval
 597             } else {
 598                 place.llval
 599             };
 600
 601             for (i, (decl, ty)) in mir.upvar_decls.iter().zip(upvar_tys).enumerate() {
 602                 let byte_offset_of_var_in_env = closure_layout.fields.offset(i).bytes();
 603
 604                 let ops = unsafe {
 605                     [llvm::LLVMRustDIBuilderCreateOpDeref(),
 606                      llvm::LLVMRustDIBuilderCreateOpPlusUconst(),
 607                      byte_offset_of_var_in_env as i64,
 608                      llvm::LLVMRustDIBuilderCreateOpDeref()]
 609                 };
 610
 611                 // The environment and the capture can each be indirect.
 612
 613                 // FIXME(eddyb) see above why we have to keep
 614                 // a pointer in an alloca for debuginfo atm.
 615                 let mut ops = if env_ref || true { &ops[..] } else { &ops[1..] };
 616
 617                 let ty = if let (true, &ty::TyRef(_, mt)) = (decl.by_ref, &ty.sty) {
 618                     mt.ty
 619                 } else {
 620                     ops = &ops[..ops.len() - 1];
 621                     ty
 622                 };
 623
 624                 let variable_access = VariableAccess::IndirectVariable {
 625                     alloca: env_ptr,
 626                     address_operations: &ops
 627                 };
 628                 declare_local(
 629                     bx,
 630                     &fx.debug_context,
 631                     decl.debug_name,
 632                     ty,
 633                     scope,
 634                     variable_access,
 635                     VariableKind::CapturedVariable,
 636                     DUMMY_SP
 637                 );
 638             }
 639         });
 640         LocalRef::Place(place)
 641     }).collect()
 642 }
 643
 644 mod analyze;
 645 mod block;
 646 mod constant;
 647 pub mod place;
 648 pub mod operand;
 649 mod rvalue;
 650 mod statement;