1077 lines
45 KiB
Rust
1077 lines
45 KiB
Rust
//! Propagates constants for early reporting of statically known
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//! assertion failures
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use std::cell::Cell;
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use rustc_ast::ast::Mutability;
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use rustc_hir::def::DefKind;
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use rustc_hir::HirId;
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use rustc_index::bit_set::BitSet;
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use rustc_index::vec::IndexVec;
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use rustc_middle::mir::interpret::{InterpResult, Scalar};
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use rustc_middle::mir::visit::{
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MutVisitor, MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor,
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};
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use rustc_middle::mir::{
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AggregateKind, AssertKind, BasicBlock, BinOp, Body, ClearCrossCrate, Constant, Local,
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LocalDecl, LocalKind, Location, Operand, Place, Rvalue, SourceInfo, SourceScope,
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SourceScopeData, Statement, StatementKind, Terminator, TerminatorKind, UnOp, RETURN_PLACE,
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};
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use rustc_middle::ty::layout::{HasTyCtxt, LayoutError, TyAndLayout};
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use rustc_middle::ty::subst::{InternalSubsts, Subst};
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use rustc_middle::ty::{self, ConstKind, Instance, ParamEnv, Ty, TyCtxt, TypeFoldable};
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use rustc_session::lint;
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use rustc_span::{def_id::DefId, Span};
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use rustc_target::abi::{HasDataLayout, LayoutOf, Size, TargetDataLayout};
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use rustc_trait_selection::traits;
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use crate::const_eval::error_to_const_error;
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use crate::interpret::{
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self, compile_time_machine, intern_const_alloc_recursive, AllocId, Allocation, Frame, ImmTy,
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Immediate, InternKind, InterpCx, LocalState, LocalValue, Memory, MemoryKind, OpTy,
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Operand as InterpOperand, PlaceTy, Pointer, ScalarMaybeUninit, StackPopCleanup,
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};
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use crate::transform::{MirPass, MirSource};
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/// The maximum number of bytes that we'll allocate space for a return value.
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const MAX_ALLOC_LIMIT: u64 = 1024;
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/// Macro for machine-specific `InterpError` without allocation.
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/// (These will never be shown to the user, but they help diagnose ICEs.)
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macro_rules! throw_machine_stop_str {
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($($tt:tt)*) => {{
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// We make a new local type for it. The type itself does not carry any information,
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// but its vtable (for the `MachineStopType` trait) does.
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struct Zst;
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// Printing this type shows the desired string.
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impl std::fmt::Display for Zst {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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write!(f, $($tt)*)
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}
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}
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impl rustc_middle::mir::interpret::MachineStopType for Zst {}
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throw_machine_stop!(Zst)
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}};
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}
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pub struct ConstProp;
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impl<'tcx> MirPass<'tcx> for ConstProp {
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fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut Body<'tcx>) {
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// will be evaluated by miri and produce its errors there
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if source.promoted.is_some() {
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return;
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}
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use rustc_middle::hir::map::blocks::FnLikeNode;
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let hir_id = tcx.hir().as_local_hir_id(source.def_id().expect_local());
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let is_fn_like = FnLikeNode::from_node(tcx.hir().get(hir_id)).is_some();
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let is_assoc_const = tcx.def_kind(source.def_id()) == DefKind::AssocConst;
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// Only run const prop on functions, methods, closures and associated constants
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if !is_fn_like && !is_assoc_const {
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// skip anon_const/statics/consts because they'll be evaluated by miri anyway
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trace!("ConstProp skipped for {:?}", source.def_id());
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return;
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}
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let is_generator = tcx.type_of(source.def_id()).is_generator();
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// FIXME(welseywiser) const prop doesn't work on generators because of query cycles
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// computing their layout.
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if is_generator {
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trace!("ConstProp skipped for generator {:?}", source.def_id());
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return;
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}
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// Check if it's even possible to satisfy the 'where' clauses
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// for this item.
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// This branch will never be taken for any normal function.
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// However, it's possible to `#!feature(trivial_bounds)]` to write
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// a function with impossible to satisfy clauses, e.g.:
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// `fn foo() where String: Copy {}`
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//
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// We don't usually need to worry about this kind of case,
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// since we would get a compilation error if the user tried
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// to call it. However, since we can do const propagation
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// even without any calls to the function, we need to make
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// sure that it even makes sense to try to evaluate the body.
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// If there are unsatisfiable where clauses, then all bets are
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// off, and we just give up.
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//
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// We manually filter the predicates, skipping anything that's not
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// "global". We are in a potentially generic context
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// (e.g. we are evaluating a function without substituting generic
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// parameters, so this filtering serves two purposes:
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//
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// 1. We skip evaluating any predicates that we would
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// never be able prove are unsatisfiable (e.g. `<T as Foo>`
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// 2. We avoid trying to normalize predicates involving generic
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// parameters (e.g. `<T as Foo>::MyItem`). This can confuse
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// the normalization code (leading to cycle errors), since
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// it's usually never invoked in this way.
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let predicates = tcx
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.predicates_of(source.def_id())
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.predicates
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.iter()
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.filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
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if !traits::normalize_and_test_predicates(
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tcx,
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traits::elaborate_predicates(tcx, predicates).map(|o| o.predicate).collect(),
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) {
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trace!("ConstProp skipped for {:?}: found unsatisfiable predicates", source.def_id());
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return;
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}
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trace!("ConstProp starting for {:?}", source.def_id());
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let dummy_body = &Body::new(
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body.basic_blocks().clone(),
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body.source_scopes.clone(),
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body.local_decls.clone(),
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Default::default(),
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body.arg_count,
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Default::default(),
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tcx.def_span(source.def_id()),
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Default::default(),
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body.generator_kind,
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);
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// FIXME(oli-obk, eddyb) Optimize locals (or even local paths) to hold
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// constants, instead of just checking for const-folding succeeding.
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// That would require an uniform one-def no-mutation analysis
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// and RPO (or recursing when needing the value of a local).
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let mut optimization_finder = ConstPropagator::new(body, dummy_body, tcx, source);
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optimization_finder.visit_body(body);
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trace!("ConstProp done for {:?}", source.def_id());
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}
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}
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struct ConstPropMachine<'mir, 'tcx> {
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/// The virtual call stack.
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stack: Vec<Frame<'mir, 'tcx, (), ()>>,
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}
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impl<'mir, 'tcx> ConstPropMachine<'mir, 'tcx> {
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fn new() -> Self {
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Self { stack: Vec::new() }
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}
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}
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impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx> {
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compile_time_machine!(<'mir, 'tcx>);
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type MemoryExtra = ();
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fn find_mir_or_eval_fn(
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_ecx: &mut InterpCx<'mir, 'tcx, Self>,
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_instance: ty::Instance<'tcx>,
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_args: &[OpTy<'tcx>],
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_ret: Option<(PlaceTy<'tcx>, BasicBlock)>,
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_unwind: Option<BasicBlock>,
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) -> InterpResult<'tcx, Option<&'mir Body<'tcx>>> {
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Ok(None)
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}
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fn call_intrinsic(
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_ecx: &mut InterpCx<'mir, 'tcx, Self>,
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_instance: ty::Instance<'tcx>,
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_args: &[OpTy<'tcx>],
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_ret: Option<(PlaceTy<'tcx>, BasicBlock)>,
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_unwind: Option<BasicBlock>,
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) -> InterpResult<'tcx> {
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throw_machine_stop_str!("calling intrinsics isn't supported in ConstProp")
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}
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fn assert_panic(
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_ecx: &mut InterpCx<'mir, 'tcx, Self>,
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_msg: &rustc_middle::mir::AssertMessage<'tcx>,
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_unwind: Option<rustc_middle::mir::BasicBlock>,
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) -> InterpResult<'tcx> {
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bug!("panics terminators are not evaluated in ConstProp")
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}
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fn ptr_to_int(_mem: &Memory<'mir, 'tcx, Self>, _ptr: Pointer) -> InterpResult<'tcx, u64> {
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throw_unsup!(ReadPointerAsBytes)
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}
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fn binary_ptr_op(
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_ecx: &InterpCx<'mir, 'tcx, Self>,
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_bin_op: BinOp,
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_left: ImmTy<'tcx>,
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_right: ImmTy<'tcx>,
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) -> InterpResult<'tcx, (Scalar, bool, Ty<'tcx>)> {
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// We can't do this because aliasing of memory can differ between const eval and llvm
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throw_machine_stop_str!("pointer arithmetic or comparisons aren't supported in ConstProp")
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}
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fn box_alloc(
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_ecx: &mut InterpCx<'mir, 'tcx, Self>,
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_dest: PlaceTy<'tcx>,
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) -> InterpResult<'tcx> {
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throw_machine_stop_str!("can't const prop heap allocations")
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}
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fn access_local(
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_ecx: &InterpCx<'mir, 'tcx, Self>,
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frame: &Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>,
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local: Local,
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) -> InterpResult<'tcx, InterpOperand<Self::PointerTag>> {
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let l = &frame.locals[local];
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if l.value == LocalValue::Uninitialized {
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throw_machine_stop_str!("tried to access an uninitialized local")
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}
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l.access()
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}
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fn before_access_global(
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_memory_extra: &(),
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_alloc_id: AllocId,
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allocation: &Allocation<Self::PointerTag, Self::AllocExtra>,
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_static_def_id: Option<DefId>,
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is_write: bool,
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) -> InterpResult<'tcx> {
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if is_write {
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throw_machine_stop_str!("can't write to global");
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}
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// If the static allocation is mutable, then we can't const prop it as its content
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// might be different at runtime.
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if allocation.mutability == Mutability::Mut {
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throw_machine_stop_str!("can't access mutable globals in ConstProp");
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}
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Ok(())
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}
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#[inline(always)]
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fn stack(
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ecx: &'a InterpCx<'mir, 'tcx, Self>,
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) -> &'a [Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>] {
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&ecx.machine.stack
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}
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#[inline(always)]
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fn stack_mut(
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ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
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) -> &'a mut Vec<Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>> {
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&mut ecx.machine.stack
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}
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}
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/// Finds optimization opportunities on the MIR.
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struct ConstPropagator<'mir, 'tcx> {
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ecx: InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>,
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tcx: TyCtxt<'tcx>,
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can_const_prop: IndexVec<Local, ConstPropMode>,
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param_env: ParamEnv<'tcx>,
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// FIXME(eddyb) avoid cloning these two fields more than once,
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// by accessing them through `ecx` instead.
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source_scopes: IndexVec<SourceScope, SourceScopeData>,
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local_decls: IndexVec<Local, LocalDecl<'tcx>>,
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// Because we have `MutVisitor` we can't obtain the `SourceInfo` from a `Location`. So we store
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// the last known `SourceInfo` here and just keep revisiting it.
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source_info: Option<SourceInfo>,
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// Locals we need to forget at the end of the current block
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locals_of_current_block: BitSet<Local>,
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}
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impl<'mir, 'tcx> LayoutOf for ConstPropagator<'mir, 'tcx> {
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type Ty = Ty<'tcx>;
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type TyAndLayout = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
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fn layout_of(&self, ty: Ty<'tcx>) -> Self::TyAndLayout {
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self.tcx.layout_of(self.param_env.and(ty))
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}
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}
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impl<'mir, 'tcx> HasDataLayout for ConstPropagator<'mir, 'tcx> {
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#[inline]
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fn data_layout(&self) -> &TargetDataLayout {
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&self.tcx.data_layout
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}
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}
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impl<'mir, 'tcx> HasTyCtxt<'tcx> for ConstPropagator<'mir, 'tcx> {
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#[inline]
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fn tcx(&self) -> TyCtxt<'tcx> {
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self.tcx
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}
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}
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impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
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fn new(
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body: &Body<'tcx>,
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dummy_body: &'mir Body<'tcx>,
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tcx: TyCtxt<'tcx>,
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source: MirSource<'tcx>,
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) -> ConstPropagator<'mir, 'tcx> {
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let def_id = source.def_id();
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let substs = &InternalSubsts::identity_for_item(tcx, def_id);
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let param_env = tcx.param_env(def_id).with_reveal_all();
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let span = tcx.def_span(def_id);
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let mut ecx = InterpCx::new(tcx.at(span), param_env, ConstPropMachine::new(), ());
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let can_const_prop = CanConstProp::check(body);
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let ret = ecx
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.layout_of(body.return_ty().subst(tcx, substs))
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.ok()
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// Don't bother allocating memory for ZST types which have no values
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// or for large values.
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.filter(|ret_layout| {
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!ret_layout.is_zst() && ret_layout.size < Size::from_bytes(MAX_ALLOC_LIMIT)
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})
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.map(|ret_layout| ecx.allocate(ret_layout, MemoryKind::Stack));
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ecx.push_stack_frame(
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Instance::new(def_id, substs),
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dummy_body,
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ret.map(Into::into),
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StackPopCleanup::None { cleanup: false },
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)
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.expect("failed to push initial stack frame");
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ConstPropagator {
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ecx,
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tcx,
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param_env,
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can_const_prop,
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// FIXME(eddyb) avoid cloning these two fields more than once,
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// by accessing them through `ecx` instead.
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source_scopes: body.source_scopes.clone(),
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//FIXME(wesleywiser) we can't steal this because `Visitor::super_visit_body()` needs it
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local_decls: body.local_decls.clone(),
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source_info: None,
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locals_of_current_block: BitSet::new_empty(body.local_decls.len()),
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}
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}
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fn get_const(&self, place: Place<'tcx>) -> Option<OpTy<'tcx>> {
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let op = self.ecx.eval_place_to_op(place, None).ok();
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// Try to read the local as an immediate so that if it is representable as a scalar, we can
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// handle it as such, but otherwise, just return the value as is.
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match op.map(|ret| self.ecx.try_read_immediate(ret)) {
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Some(Ok(Ok(imm))) => Some(imm.into()),
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_ => op,
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}
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}
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/// Remove `local` from the pool of `Locals`. Allows writing to them,
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/// but not reading from them anymore.
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fn remove_const(ecx: &mut InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>, local: Local) {
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ecx.frame_mut().locals[local] =
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LocalState { value: LocalValue::Uninitialized, layout: Cell::new(None) };
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}
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fn lint_root(&self, source_info: SourceInfo) -> Option<HirId> {
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match &self.source_scopes[source_info.scope].local_data {
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ClearCrossCrate::Set(data) => Some(data.lint_root),
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ClearCrossCrate::Clear => None,
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}
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}
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fn use_ecx<F, T>(&mut self, f: F) -> Option<T>
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where
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F: FnOnce(&mut Self) -> InterpResult<'tcx, T>,
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{
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match f(self) {
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Ok(val) => Some(val),
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Err(error) => {
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// Some errors shouldn't come up because creating them causes
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// an allocation, which we should avoid. When that happens,
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// dedicated error variants should be introduced instead.
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assert!(
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!error.kind.allocates(),
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"const-prop encountered allocating error: {}",
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error
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);
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None
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}
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}
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}
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|
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/// Returns the value, if any, of evaluating `c`.
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fn eval_constant(&mut self, c: &Constant<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> {
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// FIXME we need to revisit this for #67176
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if c.needs_subst() {
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return None;
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}
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match self.ecx.eval_const_to_op(c.literal, None) {
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Ok(op) => Some(op),
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Err(error) => {
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// Make sure errors point at the constant.
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self.ecx.set_span(c.span);
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let err = error_to_const_error(&self.ecx, error);
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if let Some(lint_root) = self.lint_root(source_info) {
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let lint_only = match c.literal.val {
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// Promoteds must lint and not error as the user didn't ask for them
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ConstKind::Unevaluated(_, _, Some(_)) => true,
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|
// Out of backwards compatibility we cannot report hard errors in unused
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|
// generic functions using associated constants of the generic parameters.
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_ => c.literal.needs_subst(),
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};
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if lint_only {
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// Out of backwards compatibility we cannot report hard errors in unused
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// generic functions using associated constants of the generic parameters.
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err.report_as_lint(
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self.ecx.tcx,
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"erroneous constant used",
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lint_root,
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Some(c.span),
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);
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} else {
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err.report_as_error(self.ecx.tcx, "erroneous constant used");
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}
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} else {
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err.report_as_error(self.ecx.tcx, "erroneous constant used");
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}
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None
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}
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}
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}
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|
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/// Returns the value, if any, of evaluating `place`.
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fn eval_place(&mut self, place: Place<'tcx>) -> Option<OpTy<'tcx>> {
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trace!("eval_place(place={:?})", place);
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self.use_ecx(|this| this.ecx.eval_place_to_op(place, None))
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}
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|
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/// Returns the value, if any, of evaluating `op`. Calls upon `eval_constant`
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/// or `eval_place`, depending on the variant of `Operand` used.
|
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fn eval_operand(&mut self, op: &Operand<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> {
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match *op {
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Operand::Constant(ref c) => self.eval_constant(c, source_info),
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Operand::Move(place) | Operand::Copy(place) => self.eval_place(place),
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}
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}
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fn report_assert_as_lint(
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&self,
|
|
lint: &'static lint::Lint,
|
|
source_info: SourceInfo,
|
|
message: &'static str,
|
|
panic: AssertKind<u64>,
|
|
) -> Option<()> {
|
|
let lint_root = self.lint_root(source_info)?;
|
|
self.tcx.struct_span_lint_hir(lint, lint_root, source_info.span, |lint| {
|
|
let mut err = lint.build(message);
|
|
err.span_label(source_info.span, format!("{:?}", panic));
|
|
err.emit()
|
|
});
|
|
None
|
|
}
|
|
|
|
fn check_unary_op(
|
|
&mut self,
|
|
op: UnOp,
|
|
arg: &Operand<'tcx>,
|
|
source_info: SourceInfo,
|
|
) -> Option<()> {
|
|
if self.use_ecx(|this| {
|
|
let val = this.ecx.read_immediate(this.ecx.eval_operand(arg, None)?)?;
|
|
let (_res, overflow, _ty) = this.ecx.overflowing_unary_op(op, val)?;
|
|
Ok(overflow)
|
|
})? {
|
|
// `AssertKind` only has an `OverflowNeg` variant, so make sure that is
|
|
// appropriate to use.
|
|
assert_eq!(op, UnOp::Neg, "Neg is the only UnOp that can overflow");
|
|
self.report_assert_as_lint(
|
|
lint::builtin::ARITHMETIC_OVERFLOW,
|
|
source_info,
|
|
"this arithmetic operation will overflow",
|
|
AssertKind::OverflowNeg,
|
|
)?;
|
|
}
|
|
|
|
Some(())
|
|
}
|
|
|
|
fn check_binary_op(
|
|
&mut self,
|
|
op: BinOp,
|
|
left: &Operand<'tcx>,
|
|
right: &Operand<'tcx>,
|
|
source_info: SourceInfo,
|
|
) -> Option<()> {
|
|
let r =
|
|
self.use_ecx(|this| this.ecx.read_immediate(this.ecx.eval_operand(right, None)?))?;
|
|
// Check for exceeding shifts *even if* we cannot evaluate the LHS.
|
|
if op == BinOp::Shr || op == BinOp::Shl {
|
|
// We need the type of the LHS. We cannot use `place_layout` as that is the type
|
|
// of the result, which for checked binops is not the same!
|
|
let left_ty = left.ty(&self.local_decls, self.tcx);
|
|
let left_size_bits = self.ecx.layout_of(left_ty).ok()?.size.bits();
|
|
let right_size = r.layout.size;
|
|
let r_bits = r.to_scalar().ok();
|
|
// This is basically `force_bits`.
|
|
let r_bits = r_bits.and_then(|r| r.to_bits_or_ptr(right_size, &self.tcx).ok());
|
|
if r_bits.map_or(false, |b| b >= left_size_bits as u128) {
|
|
self.report_assert_as_lint(
|
|
lint::builtin::ARITHMETIC_OVERFLOW,
|
|
source_info,
|
|
"this arithmetic operation will overflow",
|
|
AssertKind::Overflow(op),
|
|
)?;
|
|
}
|
|
}
|
|
|
|
// The remaining operators are handled through `overflowing_binary_op`.
|
|
if self.use_ecx(|this| {
|
|
let l = this.ecx.read_immediate(this.ecx.eval_operand(left, None)?)?;
|
|
let (_res, overflow, _ty) = this.ecx.overflowing_binary_op(op, l, r)?;
|
|
Ok(overflow)
|
|
})? {
|
|
self.report_assert_as_lint(
|
|
lint::builtin::ARITHMETIC_OVERFLOW,
|
|
source_info,
|
|
"this arithmetic operation will overflow",
|
|
AssertKind::Overflow(op),
|
|
)?;
|
|
}
|
|
|
|
Some(())
|
|
}
|
|
|
|
fn const_prop(
|
|
&mut self,
|
|
rvalue: &Rvalue<'tcx>,
|
|
place_layout: TyAndLayout<'tcx>,
|
|
source_info: SourceInfo,
|
|
place: Place<'tcx>,
|
|
) -> Option<()> {
|
|
// #66397: Don't try to eval into large places as that can cause an OOM
|
|
if place_layout.size >= Size::from_bytes(MAX_ALLOC_LIMIT) {
|
|
return None;
|
|
}
|
|
|
|
// Perform any special handling for specific Rvalue types.
|
|
// Generally, checks here fall into one of two categories:
|
|
// 1. Additional checking to provide useful lints to the user
|
|
// - In this case, we will do some validation and then fall through to the
|
|
// end of the function which evals the assignment.
|
|
// 2. Working around bugs in other parts of the compiler
|
|
// - In this case, we'll return `None` from this function to stop evaluation.
|
|
match rvalue {
|
|
// Additional checking: give lints to the user if an overflow would occur.
|
|
// We do this here and not in the `Assert` terminator as that terminator is
|
|
// only sometimes emitted (overflow checks can be disabled), but we want to always
|
|
// lint.
|
|
Rvalue::UnaryOp(op, arg) => {
|
|
trace!("checking UnaryOp(op = {:?}, arg = {:?})", op, arg);
|
|
self.check_unary_op(*op, arg, source_info)?;
|
|
}
|
|
Rvalue::BinaryOp(op, left, right) => {
|
|
trace!("checking BinaryOp(op = {:?}, left = {:?}, right = {:?})", op, left, right);
|
|
self.check_binary_op(*op, left, right, source_info)?;
|
|
}
|
|
Rvalue::CheckedBinaryOp(op, left, right) => {
|
|
trace!(
|
|
"checking CheckedBinaryOp(op = {:?}, left = {:?}, right = {:?})",
|
|
op,
|
|
left,
|
|
right
|
|
);
|
|
self.check_binary_op(*op, left, right, source_info)?;
|
|
}
|
|
|
|
// Do not try creating references (#67862)
|
|
Rvalue::Ref(_, _, place_ref) => {
|
|
trace!("skipping Ref({:?})", place_ref);
|
|
|
|
return None;
|
|
}
|
|
|
|
_ => {}
|
|
}
|
|
|
|
// FIXME we need to revisit this for #67176
|
|
if rvalue.needs_subst() {
|
|
return None;
|
|
}
|
|
|
|
self.use_ecx(|this| {
|
|
trace!("calling eval_rvalue_into_place(rvalue = {:?}, place = {:?})", rvalue, place);
|
|
this.ecx.eval_rvalue_into_place(rvalue, place)?;
|
|
Ok(())
|
|
})
|
|
}
|
|
|
|
/// Creates a new `Operand::Constant` from a `Scalar` value
|
|
fn operand_from_scalar(&self, scalar: Scalar, ty: Ty<'tcx>, span: Span) -> Operand<'tcx> {
|
|
Operand::Constant(Box::new(Constant {
|
|
span,
|
|
user_ty: None,
|
|
literal: self.tcx.mk_const(*ty::Const::from_scalar(self.tcx, scalar, ty)),
|
|
}))
|
|
}
|
|
|
|
fn replace_with_const(
|
|
&mut self,
|
|
rval: &mut Rvalue<'tcx>,
|
|
value: OpTy<'tcx>,
|
|
source_info: SourceInfo,
|
|
) {
|
|
if let Rvalue::Use(Operand::Constant(c)) = rval {
|
|
if !matches!(c.literal.val, ConstKind::Unevaluated(..)) {
|
|
trace!("skipping replace of Rvalue::Use({:?} because it is already a const", c);
|
|
return;
|
|
}
|
|
}
|
|
|
|
trace!("attepting to replace {:?} with {:?}", rval, value);
|
|
if let Err(e) = self.ecx.const_validate_operand(
|
|
value,
|
|
vec![],
|
|
// FIXME: is ref tracking too expensive?
|
|
&mut interpret::RefTracking::empty(),
|
|
/*may_ref_to_static*/ true,
|
|
) {
|
|
trace!("validation error, attempt failed: {:?}", e);
|
|
return;
|
|
}
|
|
|
|
// FIXME> figure out what to do when try_read_immediate fails
|
|
let imm = self.use_ecx(|this| this.ecx.try_read_immediate(value));
|
|
|
|
if let Some(Ok(imm)) = imm {
|
|
match *imm {
|
|
interpret::Immediate::Scalar(ScalarMaybeUninit::Scalar(scalar)) => {
|
|
*rval = Rvalue::Use(self.operand_from_scalar(
|
|
scalar,
|
|
value.layout.ty,
|
|
source_info.span,
|
|
));
|
|
}
|
|
Immediate::ScalarPair(
|
|
ScalarMaybeUninit::Scalar(one),
|
|
ScalarMaybeUninit::Scalar(two),
|
|
) => {
|
|
// Found a value represented as a pair. For now only do cont-prop if type of
|
|
// Rvalue is also a pair with two scalars. The more general case is more
|
|
// complicated to implement so we'll do it later.
|
|
// FIXME: implement the general case stated above ^.
|
|
let ty = &value.layout.ty.kind;
|
|
// Only do it for tuples
|
|
if let ty::Tuple(substs) = ty {
|
|
// Only do it if tuple is also a pair with two scalars
|
|
if substs.len() == 2 {
|
|
let opt_ty1_ty2 = self.use_ecx(|this| {
|
|
let ty1 = substs[0].expect_ty();
|
|
let ty2 = substs[1].expect_ty();
|
|
let ty_is_scalar = |ty| {
|
|
this.ecx.layout_of(ty).ok().map(|layout| layout.abi.is_scalar())
|
|
== Some(true)
|
|
};
|
|
if ty_is_scalar(ty1) && ty_is_scalar(ty2) {
|
|
Ok(Some((ty1, ty2)))
|
|
} else {
|
|
Ok(None)
|
|
}
|
|
});
|
|
|
|
if let Some(Some((ty1, ty2))) = opt_ty1_ty2 {
|
|
*rval = Rvalue::Aggregate(
|
|
Box::new(AggregateKind::Tuple),
|
|
vec![
|
|
self.operand_from_scalar(one, ty1, source_info.span),
|
|
self.operand_from_scalar(two, ty2, source_info.span),
|
|
],
|
|
);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
_ => {}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Returns `true` if and only if this `op` should be const-propagated into.
|
|
fn should_const_prop(&mut self, op: OpTy<'tcx>) -> bool {
|
|
let mir_opt_level = self.tcx.sess.opts.debugging_opts.mir_opt_level;
|
|
|
|
if mir_opt_level == 0 {
|
|
return false;
|
|
}
|
|
|
|
match *op {
|
|
interpret::Operand::Immediate(Immediate::Scalar(ScalarMaybeUninit::Scalar(s))) => {
|
|
s.is_bits()
|
|
}
|
|
interpret::Operand::Immediate(Immediate::ScalarPair(
|
|
ScalarMaybeUninit::Scalar(l),
|
|
ScalarMaybeUninit::Scalar(r),
|
|
)) => l.is_bits() && r.is_bits(),
|
|
interpret::Operand::Indirect(_) if mir_opt_level >= 2 => {
|
|
let mplace = op.assert_mem_place(&self.ecx);
|
|
intern_const_alloc_recursive(&mut self.ecx, InternKind::ConstProp, mplace, false);
|
|
true
|
|
}
|
|
_ => false,
|
|
}
|
|
}
|
|
}
|
|
|
|
/// The mode that `ConstProp` is allowed to run in for a given `Local`.
|
|
#[derive(Clone, Copy, Debug, PartialEq)]
|
|
enum ConstPropMode {
|
|
/// The `Local` can be propagated into and reads of this `Local` can also be propagated.
|
|
FullConstProp,
|
|
/// The `Local` can only be propagated into and from its own block.
|
|
OnlyInsideOwnBlock,
|
|
/// The `Local` can be propagated into but reads cannot be propagated.
|
|
OnlyPropagateInto,
|
|
/// No propagation is allowed at all.
|
|
NoPropagation,
|
|
}
|
|
|
|
struct CanConstProp {
|
|
can_const_prop: IndexVec<Local, ConstPropMode>,
|
|
// False at the beginning. Once set, no more assignments are allowed to that local.
|
|
found_assignment: BitSet<Local>,
|
|
// Cache of locals' information
|
|
local_kinds: IndexVec<Local, LocalKind>,
|
|
}
|
|
|
|
impl CanConstProp {
|
|
/// Returns true if `local` can be propagated
|
|
fn check(body: &Body<'_>) -> IndexVec<Local, ConstPropMode> {
|
|
let mut cpv = CanConstProp {
|
|
can_const_prop: IndexVec::from_elem(ConstPropMode::FullConstProp, &body.local_decls),
|
|
found_assignment: BitSet::new_empty(body.local_decls.len()),
|
|
local_kinds: IndexVec::from_fn_n(
|
|
|local| body.local_kind(local),
|
|
body.local_decls.len(),
|
|
),
|
|
};
|
|
for (local, val) in cpv.can_const_prop.iter_enumerated_mut() {
|
|
// Cannot use args at all
|
|
// Cannot use locals because if x < y { y - x } else { x - y } would
|
|
// lint for x != y
|
|
// FIXME(oli-obk): lint variables until they are used in a condition
|
|
// FIXME(oli-obk): lint if return value is constant
|
|
if cpv.local_kinds[local] == LocalKind::Arg {
|
|
*val = ConstPropMode::OnlyPropagateInto;
|
|
trace!(
|
|
"local {:?} can't be const propagated because it's a function argument",
|
|
local
|
|
);
|
|
} else if cpv.local_kinds[local] == LocalKind::Var {
|
|
*val = ConstPropMode::OnlyInsideOwnBlock;
|
|
trace!(
|
|
"local {:?} will only be propagated inside its block, because it's a user variable",
|
|
local
|
|
);
|
|
}
|
|
}
|
|
cpv.visit_body(&body);
|
|
cpv.can_const_prop
|
|
}
|
|
}
|
|
|
|
impl<'tcx> Visitor<'tcx> for CanConstProp {
|
|
fn visit_local(&mut self, &local: &Local, context: PlaceContext, _: Location) {
|
|
use rustc_middle::mir::visit::PlaceContext::*;
|
|
match context {
|
|
// Projections are fine, because `&mut foo.x` will be caught by
|
|
// `MutatingUseContext::Borrow` elsewhere.
|
|
MutatingUse(MutatingUseContext::Projection)
|
|
// These are just stores, where the storing is not propagatable, but there may be later
|
|
// mutations of the same local via `Store`
|
|
| MutatingUse(MutatingUseContext::Call)
|
|
// Actual store that can possibly even propagate a value
|
|
| MutatingUse(MutatingUseContext::Store) => {
|
|
if !self.found_assignment.insert(local) {
|
|
match &mut self.can_const_prop[local] {
|
|
// If the local can only get propagated in its own block, then we don't have
|
|
// to worry about multiple assignments, as we'll nuke the const state at the
|
|
// end of the block anyway, and inside the block we overwrite previous
|
|
// states as applicable.
|
|
ConstPropMode::OnlyInsideOwnBlock => {}
|
|
other => {
|
|
trace!(
|
|
"local {:?} can't be propagated because of multiple assignments",
|
|
local,
|
|
);
|
|
*other = ConstPropMode::NoPropagation;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
// Reading constants is allowed an arbitrary number of times
|
|
NonMutatingUse(NonMutatingUseContext::Copy)
|
|
| NonMutatingUse(NonMutatingUseContext::Move)
|
|
| NonMutatingUse(NonMutatingUseContext::Inspect)
|
|
| NonMutatingUse(NonMutatingUseContext::Projection)
|
|
| NonUse(_) => {}
|
|
|
|
// These could be propagated with a smarter analysis or just some careful thinking about
|
|
// whether they'd be fine right now.
|
|
MutatingUse(MutatingUseContext::AsmOutput)
|
|
| MutatingUse(MutatingUseContext::Yield)
|
|
| MutatingUse(MutatingUseContext::Drop)
|
|
| MutatingUse(MutatingUseContext::Retag)
|
|
// These can't ever be propagated under any scheme, as we can't reason about indirect
|
|
// mutation.
|
|
| NonMutatingUse(NonMutatingUseContext::SharedBorrow)
|
|
| NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
|
|
| NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
|
|
| NonMutatingUse(NonMutatingUseContext::AddressOf)
|
|
| MutatingUse(MutatingUseContext::Borrow)
|
|
| MutatingUse(MutatingUseContext::AddressOf) => {
|
|
trace!("local {:?} can't be propagaged because it's used: {:?}", local, context);
|
|
self.can_const_prop[local] = ConstPropMode::NoPropagation;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
|
|
fn tcx(&self) -> TyCtxt<'tcx> {
|
|
self.tcx
|
|
}
|
|
|
|
fn visit_body(&mut self, body: &mut Body<'tcx>) {
|
|
for (bb, data) in body.basic_blocks_mut().iter_enumerated_mut() {
|
|
self.visit_basic_block_data(bb, data);
|
|
}
|
|
}
|
|
|
|
fn visit_constant(&mut self, constant: &mut Constant<'tcx>, location: Location) {
|
|
trace!("visit_constant: {:?}", constant);
|
|
self.super_constant(constant, location);
|
|
self.eval_constant(constant, self.source_info.unwrap());
|
|
}
|
|
|
|
fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
|
|
trace!("visit_statement: {:?}", statement);
|
|
let source_info = statement.source_info;
|
|
self.ecx.set_span(source_info.span);
|
|
self.source_info = Some(source_info);
|
|
if let StatementKind::Assign(box (place, ref mut rval)) = statement.kind {
|
|
let place_ty: Ty<'tcx> = place.ty(&self.local_decls, self.tcx).ty;
|
|
if let Ok(place_layout) = self.tcx.layout_of(self.param_env.and(place_ty)) {
|
|
let can_const_prop = self.can_const_prop[place.local];
|
|
if let Some(()) = self.const_prop(rval, place_layout, source_info, place) {
|
|
if can_const_prop != ConstPropMode::NoPropagation {
|
|
// This will return None for variables that are from other blocks,
|
|
// so it should be okay to propagate from here on down.
|
|
if let Some(value) = self.get_const(place) {
|
|
if self.should_const_prop(value) {
|
|
trace!("replacing {:?} with {:?}", rval, value);
|
|
self.replace_with_const(rval, value, statement.source_info);
|
|
if can_const_prop == ConstPropMode::FullConstProp
|
|
|| can_const_prop == ConstPropMode::OnlyInsideOwnBlock
|
|
{
|
|
trace!("propagated into {:?}", place);
|
|
}
|
|
}
|
|
if can_const_prop == ConstPropMode::OnlyInsideOwnBlock {
|
|
trace!(
|
|
"found local restricted to its block. Will remove it from const-prop after block is finished. Local: {:?}",
|
|
place.local
|
|
);
|
|
self.locals_of_current_block.insert(place.local);
|
|
}
|
|
}
|
|
}
|
|
if can_const_prop == ConstPropMode::OnlyPropagateInto
|
|
|| can_const_prop == ConstPropMode::NoPropagation
|
|
{
|
|
trace!("can't propagate into {:?}", place);
|
|
if place.local != RETURN_PLACE {
|
|
Self::remove_const(&mut self.ecx, place.local);
|
|
}
|
|
}
|
|
} else {
|
|
// Const prop failed, so erase the destination, ensuring that whatever happens
|
|
// from here on, does not know about the previous value.
|
|
// This is important in case we have
|
|
// ```rust
|
|
// let mut x = 42;
|
|
// x = SOME_MUTABLE_STATIC;
|
|
// // x must now be undefined
|
|
// ```
|
|
// FIXME: we overzealously erase the entire local, because that's easier to
|
|
// implement.
|
|
trace!(
|
|
"propagation into {:?} failed.
|
|
Nuking the entire site from orbit, it's the only way to be sure",
|
|
place,
|
|
);
|
|
Self::remove_const(&mut self.ecx, place.local);
|
|
}
|
|
}
|
|
} else {
|
|
match statement.kind {
|
|
StatementKind::StorageLive(local) | StatementKind::StorageDead(local) => {
|
|
let frame = self.ecx.frame_mut();
|
|
frame.locals[local].value =
|
|
if let StatementKind::StorageLive(_) = statement.kind {
|
|
LocalValue::Uninitialized
|
|
} else {
|
|
LocalValue::Dead
|
|
};
|
|
}
|
|
_ => {}
|
|
}
|
|
}
|
|
|
|
self.super_statement(statement, location);
|
|
}
|
|
|
|
fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, location: Location) {
|
|
let source_info = terminator.source_info;
|
|
self.ecx.set_span(source_info.span);
|
|
self.source_info = Some(source_info);
|
|
self.super_terminator(terminator, location);
|
|
match &mut terminator.kind {
|
|
TerminatorKind::Assert { expected, ref msg, ref mut cond, .. } => {
|
|
if let Some(value) = self.eval_operand(&cond, source_info) {
|
|
trace!("assertion on {:?} should be {:?}", value, expected);
|
|
let expected = ScalarMaybeUninit::from(Scalar::from_bool(*expected));
|
|
let value_const = self.ecx.read_scalar(value).unwrap();
|
|
if expected != value_const {
|
|
// Poison all places this operand references so that further code
|
|
// doesn't use the invalid value
|
|
match cond {
|
|
Operand::Move(ref place) | Operand::Copy(ref place) => {
|
|
Self::remove_const(&mut self.ecx, place.local);
|
|
}
|
|
Operand::Constant(_) => {}
|
|
}
|
|
let msg = match msg {
|
|
AssertKind::DivisionByZero => AssertKind::DivisionByZero,
|
|
AssertKind::RemainderByZero => AssertKind::RemainderByZero,
|
|
AssertKind::BoundsCheck { ref len, ref index } => {
|
|
let len =
|
|
self.eval_operand(len, source_info).expect("len must be const");
|
|
let len = self
|
|
.ecx
|
|
.read_scalar(len)
|
|
.unwrap()
|
|
.to_machine_usize(&self.tcx)
|
|
.unwrap();
|
|
let index = self
|
|
.eval_operand(index, source_info)
|
|
.expect("index must be const");
|
|
let index = self
|
|
.ecx
|
|
.read_scalar(index)
|
|
.unwrap()
|
|
.to_machine_usize(&self.tcx)
|
|
.unwrap();
|
|
AssertKind::BoundsCheck { len, index }
|
|
}
|
|
// Overflow is are already covered by checks on the binary operators.
|
|
AssertKind::Overflow(_) | AssertKind::OverflowNeg => return,
|
|
// Need proper const propagator for these.
|
|
_ => return,
|
|
};
|
|
self.report_assert_as_lint(
|
|
lint::builtin::UNCONDITIONAL_PANIC,
|
|
source_info,
|
|
"this operation will panic at runtime",
|
|
msg,
|
|
);
|
|
} else {
|
|
if self.should_const_prop(value) {
|
|
if let ScalarMaybeUninit::Scalar(scalar) = value_const {
|
|
*cond = self.operand_from_scalar(
|
|
scalar,
|
|
self.tcx.types.bool,
|
|
source_info.span,
|
|
);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
TerminatorKind::SwitchInt { ref mut discr, switch_ty, .. } => {
|
|
if let Some(value) = self.eval_operand(&discr, source_info) {
|
|
if self.should_const_prop(value) {
|
|
if let ScalarMaybeUninit::Scalar(scalar) =
|
|
self.ecx.read_scalar(value).unwrap()
|
|
{
|
|
*discr = self.operand_from_scalar(scalar, switch_ty, source_info.span);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
// None of these have Operands to const-propagate
|
|
TerminatorKind::Goto { .. }
|
|
| TerminatorKind::Resume
|
|
| TerminatorKind::Abort
|
|
| TerminatorKind::Return
|
|
| TerminatorKind::Unreachable
|
|
| TerminatorKind::Drop { .. }
|
|
| TerminatorKind::DropAndReplace { .. }
|
|
| TerminatorKind::Yield { .. }
|
|
| TerminatorKind::GeneratorDrop
|
|
| TerminatorKind::FalseEdges { .. }
|
|
| TerminatorKind::FalseUnwind { .. }
|
|
| TerminatorKind::InlineAsm { .. } => {}
|
|
// Every argument in our function calls can be const propagated.
|
|
TerminatorKind::Call { ref mut args, .. } => {
|
|
let mir_opt_level = self.tcx.sess.opts.debugging_opts.mir_opt_level;
|
|
// Constant Propagation into function call arguments is gated
|
|
// under mir-opt-level 2, because LLVM codegen gives performance
|
|
// regressions with it.
|
|
if mir_opt_level >= 2 {
|
|
for opr in args {
|
|
/*
|
|
The following code would appear to be incomplete, because
|
|
the function `Operand::place()` returns `None` if the
|
|
`Operand` is of the variant `Operand::Constant`. In this
|
|
context however, that variant will never appear. This is why:
|
|
|
|
When constructing the MIR, all function call arguments are
|
|
copied into `Locals` of `LocalKind::Temp`. At least, all arguments
|
|
that are not unsized (Less than 0.1% are unsized. See #71170
|
|
to learn more about those).
|
|
|
|
This means that, conversely, all `Operands` found as function call
|
|
arguments are of the variant `Operand::Copy`. This allows us to
|
|
simplify our handling of `Operands` in this case.
|
|
*/
|
|
if let Some(l) = opr.place() {
|
|
if let Some(value) = self.get_const(l) {
|
|
if self.should_const_prop(value) {
|
|
// FIXME(felix91gr): this code only handles `Scalar` cases.
|
|
// For now, we're not handling `ScalarPair` cases because
|
|
// doing so here would require a lot of code duplication.
|
|
// We should hopefully generalize `Operand` handling into a fn,
|
|
// and use it to do const-prop here and everywhere else
|
|
// where it makes sense.
|
|
if let interpret::Operand::Immediate(
|
|
interpret::Immediate::Scalar(ScalarMaybeUninit::Scalar(
|
|
scalar,
|
|
)),
|
|
) = *value
|
|
{
|
|
*opr = self.operand_from_scalar(
|
|
scalar,
|
|
value.layout.ty,
|
|
source_info.span,
|
|
);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
// We remove all Locals which are restricted in propagation to their containing blocks.
|
|
for local in self.locals_of_current_block.iter() {
|
|
Self::remove_const(&mut self.ecx, local);
|
|
}
|
|
self.locals_of_current_block.clear();
|
|
}
|
|
}
|