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mod.rs
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use crate::traits::*;
use rustc_errors::ErrorReported;
use rustc_middle::mir;
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt, TyAndLayout};
use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
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: 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>,
/// 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)
}
}
}
///////////////////////////////////////////////////////////////////////////
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 = FnAbi::of_instance(cx, instance, &[]);
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);
// Allocate a `Block` for every basic block, except
// the start block, if nothing loops back to it.
let reentrant_start_block = !mir.predecessors()[mir::START_BLOCK].is_empty();
let cached_llbbs: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>> =
mir.basic_blocks()
.indices()
.map(|bb| {
if bb == mir::START_BLOCK && !reentrant_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,
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(ErrorReported) | 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);
// Branch to the START block, if it's not the entry block.
if reentrant_start_block {
bx.br(fx.llbb(mir::START_BLOCK));
}
// Codegen the body of each block using reverse postorder
// FIXME(eddyb) reuse RPO iterator between `analysis` and this.
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 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 tupled_arg_tys = match arg_ty.kind() {
ty::Tuple(tys) => tys,
_ => 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);
}
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()) {
assert_eq!(
fx.fn_abi.args.len(),
args.len() + 1,
"#[track_caller] fn's must have 1 more argument in their ABI than in their MIR",
);
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;