diff options
Diffstat (limited to 'compiler/rustc_codegen_ssa/src/mir/mod.rs')
| -rw-r--r-- | compiler/rustc_codegen_ssa/src/mir/mod.rs | 410 |
1 files changed, 410 insertions, 0 deletions
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs new file mode 100644 index 000000000..8ee375fa9 --- /dev/null +++ b/compiler/rustc_codegen_ssa/src/mir/mod.rs @@ -0,0 +1,410 @@ +use crate::traits::*; +use rustc_middle::mir; +use rustc_middle::mir::interpret::ErrorHandled; +use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, TyAndLayout}; +use rustc_middle::ty::{self, Instance, Ty, TypeFoldable, TypeVisitable}; +use rustc_target::abi::call::{FnAbi, PassMode}; + +use std::iter; + +use rustc_index::bit_set::BitSet; +use rustc_index::vec::IndexVec; + +use self::debuginfo::{FunctionDebugContext, PerLocalVarDebugInfo}; +use self::place::PlaceRef; +use rustc_middle::mir::traversal; + +use self::operand::{OperandRef, OperandValue}; + +/// Master context for codegenning from MIR. +pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> { + instance: Instance<'tcx>, + + mir: &'tcx mir::Body<'tcx>, + + debug_context: Option<FunctionDebugContext<Bx::DIScope, Bx::DILocation>>, + + llfn: Bx::Function, + + cx: &'a Bx::CodegenCx, + + fn_abi: &'tcx FnAbi<'tcx, Ty<'tcx>>, + + /// When unwinding is initiated, we have to store this personality + /// value somewhere so that we can load it and re-use it in the + /// resume instruction. The personality is (afaik) some kind of + /// value used for C++ unwinding, which must filter by type: we + /// don't really care about it very much. Anyway, this value + /// contains an alloca into which the personality is stored and + /// then later loaded when generating the DIVERGE_BLOCK. + personality_slot: Option<PlaceRef<'tcx, Bx::Value>>, + + /// A backend `BasicBlock` for each MIR `BasicBlock`, created lazily + /// as-needed (e.g. RPO reaching it or another block branching to it). + // FIXME(eddyb) rename `llbbs` and other `ll`-prefixed things to use a + // more backend-agnostic prefix such as `cg` (i.e. this would be `cgbbs`). + cached_llbbs: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>>, + + /// The funclet status of each basic block + cleanup_kinds: IndexVec<mir::BasicBlock, analyze::CleanupKind>, + + /// When targeting MSVC, this stores the cleanup info for each funclet BB. + /// This is initialized at the same time as the `landing_pads` entry for the + /// funclets' head block, i.e. when needed by an unwind / `cleanup_ret` edge. + funclets: IndexVec<mir::BasicBlock, Option<Bx::Funclet>>, + + /// This stores the cached landing/cleanup pad block for a given BB. + // FIXME(eddyb) rename this to `eh_pads`. + landing_pads: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>>, + + /// Cached unreachable block + unreachable_block: Option<Bx::BasicBlock>, + + /// Cached double unwind guarding block + double_unwind_guard: Option<Bx::BasicBlock>, + + /// The location where each MIR arg/var/tmp/ret is stored. This is + /// usually an `PlaceRef` representing an alloca, but not always: + /// sometimes we can skip the alloca and just store the value + /// directly using an `OperandRef`, which makes for tighter LLVM + /// IR. The conditions for using an `OperandRef` are as follows: + /// + /// - the type of the local must be judged "immediate" by `is_llvm_immediate` + /// - the operand must never be referenced indirectly + /// - we should not take its address using the `&` operator + /// - nor should it appear in a place path like `tmp.a` + /// - the operand must be defined by an rvalue that can generate immediate + /// values + /// + /// Avoiding allocs can also be important for certain intrinsics, + /// notably `expect`. + locals: IndexVec<mir::Local, LocalRef<'tcx, Bx::Value>>, + + /// All `VarDebugInfo` from the MIR body, partitioned by `Local`. + /// This is `None` if no var`#[non_exhaustive]`iable debuginfo/names are needed. + per_local_var_debug_info: + Option<IndexVec<mir::Local, Vec<PerLocalVarDebugInfo<'tcx, Bx::DIVariable>>>>, + + /// Caller location propagated if this function has `#[track_caller]`. + caller_location: Option<OperandRef<'tcx, Bx::Value>>, +} + +impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { + pub fn monomorphize<T>(&self, value: T) -> T + where + T: Copy + TypeFoldable<'tcx>, + { + debug!("monomorphize: self.instance={:?}", self.instance); + self.instance.subst_mir_and_normalize_erasing_regions( + self.cx.tcx(), + ty::ParamEnv::reveal_all(), + value, + ) + } +} + +enum LocalRef<'tcx, V> { + Place(PlaceRef<'tcx, V>), + /// `UnsizedPlace(p)`: `p` itself is a thin pointer (indirect place). + /// `*p` is the fat pointer that references the actual unsized place. + /// Every time it is initialized, we have to reallocate the place + /// and update the fat pointer. That's the reason why it is indirect. + UnsizedPlace(PlaceRef<'tcx, V>), + Operand(Option<OperandRef<'tcx, V>>), +} + +impl<'a, 'tcx, V: CodegenObject> LocalRef<'tcx, V> { + fn new_operand<Bx: BuilderMethods<'a, 'tcx, Value = V>>( + bx: &mut Bx, + layout: TyAndLayout<'tcx>, + ) -> LocalRef<'tcx, V> { + if layout.is_zst() { + // Zero-size temporaries aren't always initialized, which + // doesn't matter because they don't contain data, but + // we need something in the operand. + LocalRef::Operand(Some(OperandRef::new_zst(bx, layout))) + } else { + LocalRef::Operand(None) + } + } +} + +/////////////////////////////////////////////////////////////////////////// + +#[instrument(level = "debug", skip(cx))] +pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( + cx: &'a Bx::CodegenCx, + instance: Instance<'tcx>, +) { + assert!(!instance.substs.needs_infer()); + + let llfn = cx.get_fn(instance); + + let mir = cx.tcx().instance_mir(instance.def); + + let fn_abi = cx.fn_abi_of_instance(instance, ty::List::empty()); + debug!("fn_abi: {:?}", fn_abi); + + let debug_context = cx.create_function_debug_context(instance, &fn_abi, llfn, &mir); + + let start_llbb = Bx::append_block(cx, llfn, "start"); + let mut bx = Bx::build(cx, start_llbb); + + if mir.basic_blocks().iter().any(|bb| bb.is_cleanup) { + bx.set_personality_fn(cx.eh_personality()); + } + + let cleanup_kinds = analyze::cleanup_kinds(&mir); + let cached_llbbs: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>> = mir + .basic_blocks() + .indices() + .map(|bb| if bb == mir::START_BLOCK { Some(start_llbb) } else { None }) + .collect(); + + let mut fx = FunctionCx { + instance, + mir, + llfn, + fn_abi, + cx, + personality_slot: None, + cached_llbbs, + unreachable_block: None, + double_unwind_guard: None, + cleanup_kinds, + landing_pads: IndexVec::from_elem(None, mir.basic_blocks()), + funclets: IndexVec::from_fn_n(|_| None, mir.basic_blocks().len()), + locals: IndexVec::new(), + debug_context, + per_local_var_debug_info: None, + caller_location: None, + }; + + fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut bx); + + // Evaluate all required consts; codegen later assumes that CTFE will never fail. + let mut all_consts_ok = true; + for const_ in &mir.required_consts { + if let Err(err) = fx.eval_mir_constant(const_) { + all_consts_ok = false; + match err { + // errored or at least linted + ErrorHandled::Reported(_) | ErrorHandled::Linted => {} + ErrorHandled::TooGeneric => { + span_bug!(const_.span, "codgen encountered polymorphic constant: {:?}", err) + } + } + } + } + if !all_consts_ok { + // We leave the IR in some half-built state here, and rely on this code not even being + // submitted to LLVM once an error was raised. + return; + } + + let memory_locals = analyze::non_ssa_locals(&fx); + + // Allocate variable and temp allocas + fx.locals = { + let args = arg_local_refs(&mut bx, &mut fx, &memory_locals); + + let mut allocate_local = |local| { + let decl = &mir.local_decls[local]; + let layout = bx.layout_of(fx.monomorphize(decl.ty)); + assert!(!layout.ty.has_erasable_regions()); + + if local == mir::RETURN_PLACE && fx.fn_abi.ret.is_indirect() { + debug!("alloc: {:?} (return place) -> place", local); + let llretptr = bx.get_param(0); + return LocalRef::Place(PlaceRef::new_sized(llretptr, layout)); + } + + if memory_locals.contains(local) { + debug!("alloc: {:?} -> place", local); + if layout.is_unsized() { + LocalRef::UnsizedPlace(PlaceRef::alloca_unsized_indirect(&mut bx, layout)) + } else { + LocalRef::Place(PlaceRef::alloca(&mut bx, layout)) + } + } else { + debug!("alloc: {:?} -> operand", local); + LocalRef::new_operand(&mut bx, layout) + } + }; + + let retptr = allocate_local(mir::RETURN_PLACE); + iter::once(retptr) + .chain(args.into_iter()) + .chain(mir.vars_and_temps_iter().map(allocate_local)) + .collect() + }; + + // Apply debuginfo to the newly allocated locals. + fx.debug_introduce_locals(&mut bx); + + // Codegen the body of each block using reverse postorder + for (bb, _) in traversal::reverse_postorder(&mir) { + fx.codegen_block(bb); + } +} + +/// Produces, for each argument, a `Value` pointing at the +/// argument's value. As arguments are places, these are always +/// indirect. +fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( + bx: &mut Bx, + fx: &mut FunctionCx<'a, 'tcx, Bx>, + memory_locals: &BitSet<mir::Local>, +) -> Vec<LocalRef<'tcx, Bx::Value>> { + let mir = fx.mir; + let mut idx = 0; + let mut llarg_idx = fx.fn_abi.ret.is_indirect() as usize; + + let mut num_untupled = None; + + let args = mir + .args_iter() + .enumerate() + .map(|(arg_index, local)| { + let arg_decl = &mir.local_decls[local]; + + if Some(local) == mir.spread_arg { + // This argument (e.g., the last argument in the "rust-call" ABI) + // is a tuple that was spread at the ABI level and now we have + // to reconstruct it into a tuple local variable, from multiple + // individual LLVM function arguments. + + let arg_ty = fx.monomorphize(arg_decl.ty); + let ty::Tuple(tupled_arg_tys) = arg_ty.kind() else { + bug!("spread argument isn't a tuple?!"); + }; + + let place = PlaceRef::alloca(bx, bx.layout_of(arg_ty)); + for i in 0..tupled_arg_tys.len() { + let arg = &fx.fn_abi.args[idx]; + idx += 1; + if arg.pad.is_some() { + llarg_idx += 1; + } + let pr_field = place.project_field(bx, i); + bx.store_fn_arg(arg, &mut llarg_idx, pr_field); + } + assert_eq!( + None, + num_untupled.replace(tupled_arg_tys.len()), + "Replaced existing num_tupled" + ); + + return LocalRef::Place(place); + } + + if fx.fn_abi.c_variadic && arg_index == fx.fn_abi.args.len() { + let arg_ty = fx.monomorphize(arg_decl.ty); + + let va_list = PlaceRef::alloca(bx, bx.layout_of(arg_ty)); + bx.va_start(va_list.llval); + + return LocalRef::Place(va_list); + } + + let arg = &fx.fn_abi.args[idx]; + idx += 1; + if arg.pad.is_some() { + llarg_idx += 1; + } + + if !memory_locals.contains(local) { + // We don't have to cast or keep the argument in the alloca. + // FIXME(eddyb): We should figure out how to use llvm.dbg.value instead + // of putting everything in allocas just so we can use llvm.dbg.declare. + let local = |op| LocalRef::Operand(Some(op)); + match arg.mode { + PassMode::Ignore => { + return local(OperandRef::new_zst(bx, arg.layout)); + } + PassMode::Direct(_) => { + let llarg = bx.get_param(llarg_idx); + llarg_idx += 1; + return local(OperandRef::from_immediate_or_packed_pair( + bx, llarg, arg.layout, + )); + } + PassMode::Pair(..) => { + let (a, b) = (bx.get_param(llarg_idx), bx.get_param(llarg_idx + 1)); + llarg_idx += 2; + + return local(OperandRef { + val: OperandValue::Pair(a, b), + layout: arg.layout, + }); + } + _ => {} + } + } + + if arg.is_sized_indirect() { + // Don't copy an indirect argument to an alloca, the caller + // already put it in a temporary alloca and gave it up. + // FIXME: lifetimes + let llarg = bx.get_param(llarg_idx); + llarg_idx += 1; + LocalRef::Place(PlaceRef::new_sized(llarg, arg.layout)) + } else if arg.is_unsized_indirect() { + // As the storage for the indirect argument lives during + // the whole function call, we just copy the fat pointer. + let llarg = bx.get_param(llarg_idx); + llarg_idx += 1; + let llextra = bx.get_param(llarg_idx); + llarg_idx += 1; + let indirect_operand = OperandValue::Pair(llarg, llextra); + + let tmp = PlaceRef::alloca_unsized_indirect(bx, arg.layout); + indirect_operand.store(bx, tmp); + LocalRef::UnsizedPlace(tmp) + } else { + let tmp = PlaceRef::alloca(bx, arg.layout); + bx.store_fn_arg(arg, &mut llarg_idx, tmp); + LocalRef::Place(tmp) + } + }) + .collect::<Vec<_>>(); + + if fx.instance.def.requires_caller_location(bx.tcx()) { + let mir_args = if let Some(num_untupled) = num_untupled { + // Subtract off the tupled argument that gets 'expanded' + args.len() - 1 + num_untupled + } else { + args.len() + }; + assert_eq!( + fx.fn_abi.args.len(), + mir_args + 1, + "#[track_caller] instance {:?} must have 1 more argument in their ABI than in their MIR", + fx.instance + ); + + let arg = fx.fn_abi.args.last().unwrap(); + match arg.mode { + PassMode::Direct(_) => (), + _ => bug!("caller location must be PassMode::Direct, found {:?}", arg.mode), + } + + fx.caller_location = Some(OperandRef { + val: OperandValue::Immediate(bx.get_param(llarg_idx)), + layout: arg.layout, + }); + } + + args +} + +mod analyze; +mod block; +pub mod constant; +pub mod coverageinfo; +pub mod debuginfo; +mod intrinsic; +pub mod operand; +pub mod place; +mod rvalue; +mod statement; |