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806 lines
30 KiB
Rust
806 lines
30 KiB
Rust
//! The general point of the optimizations provided here is to simplify something like:
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//!
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//! ```rust
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//! match x {
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//! Ok(x) => Ok(x),
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//! Err(x) => Err(x)
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//! }
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//! ```
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//!
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//! into just `x`.
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use crate::{simplify, MirPass};
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use itertools::Itertools as _;
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use rustc_index::{bit_set::BitSet, vec::IndexVec};
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use rustc_middle::mir::visit::{NonUseContext, PlaceContext, Visitor};
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use rustc_middle::mir::*;
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use rustc_middle::ty::{self, List, Ty, TyCtxt};
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use rustc_target::abi::VariantIdx;
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use std::iter::{once, Enumerate, Peekable};
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use std::slice::Iter;
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/// Simplifies arms of form `Variant(x) => Variant(x)` to just a move.
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///
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/// This is done by transforming basic blocks where the statements match:
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///
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/// ```rust
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/// _LOCAL_TMP = ((_LOCAL_1 as Variant ).FIELD: TY );
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/// _TMP_2 = _LOCAL_TMP;
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/// ((_LOCAL_0 as Variant).FIELD: TY) = move _TMP_2;
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/// discriminant(_LOCAL_0) = VAR_IDX;
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/// ```
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///
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/// into:
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///
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/// ```rust
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/// _LOCAL_0 = move _LOCAL_1
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/// ```
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pub struct SimplifyArmIdentity;
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#[derive(Debug)]
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struct ArmIdentityInfo<'tcx> {
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/// Storage location for the variant's field
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local_temp_0: Local,
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/// Storage location holding the variant being read from
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local_1: Local,
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/// The variant field being read from
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vf_s0: VarField<'tcx>,
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/// Index of the statement which loads the variant being read
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get_variant_field_stmt: usize,
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/// Tracks each assignment to a temporary of the variant's field
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field_tmp_assignments: Vec<(Local, Local)>,
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/// Storage location holding the variant's field that was read from
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local_tmp_s1: Local,
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/// Storage location holding the enum that we are writing to
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local_0: Local,
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/// The variant field being written to
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vf_s1: VarField<'tcx>,
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/// Storage location that the discriminant is being written to
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set_discr_local: Local,
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/// The variant being written
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set_discr_var_idx: VariantIdx,
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/// Index of the statement that should be overwritten as a move
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stmt_to_overwrite: usize,
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/// SourceInfo for the new move
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source_info: SourceInfo,
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/// Indices of matching Storage{Live,Dead} statements encountered.
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/// (StorageLive index,, StorageDead index, Local)
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storage_stmts: Vec<(usize, usize, Local)>,
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/// The statements that should be removed (turned into nops)
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stmts_to_remove: Vec<usize>,
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/// Indices of debug variables that need to be adjusted to point to
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// `{local_0}.{dbg_projection}`.
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dbg_info_to_adjust: Vec<usize>,
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/// The projection used to rewrite debug info.
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dbg_projection: &'tcx List<PlaceElem<'tcx>>,
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}
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fn get_arm_identity_info<'a, 'tcx>(
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stmts: &'a [Statement<'tcx>],
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locals_count: usize,
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debug_info: &'a [VarDebugInfo<'tcx>],
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) -> Option<ArmIdentityInfo<'tcx>> {
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// This can't possibly match unless there are at least 3 statements in the block
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// so fail fast on tiny blocks.
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if stmts.len() < 3 {
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return None;
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}
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let mut tmp_assigns = Vec::new();
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let mut nop_stmts = Vec::new();
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let mut storage_stmts = Vec::new();
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let mut storage_live_stmts = Vec::new();
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let mut storage_dead_stmts = Vec::new();
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type StmtIter<'a, 'tcx> = Peekable<Enumerate<Iter<'a, Statement<'tcx>>>>;
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fn is_storage_stmt<'tcx>(stmt: &Statement<'tcx>) -> bool {
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matches!(stmt.kind, StatementKind::StorageLive(_) | StatementKind::StorageDead(_))
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}
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/// Eats consecutive Statements which match `test`, performing the specified `action` for each.
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/// The iterator `stmt_iter` is not advanced if none were matched.
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fn try_eat<'a, 'tcx>(
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stmt_iter: &mut StmtIter<'a, 'tcx>,
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test: impl Fn(&'a Statement<'tcx>) -> bool,
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mut action: impl FnMut(usize, &'a Statement<'tcx>),
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) {
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while stmt_iter.peek().map_or(false, |(_, stmt)| test(stmt)) {
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let (idx, stmt) = stmt_iter.next().unwrap();
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action(idx, stmt);
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}
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}
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/// Eats consecutive `StorageLive` and `StorageDead` Statements.
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/// The iterator `stmt_iter` is not advanced if none were found.
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fn try_eat_storage_stmts<'a, 'tcx>(
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stmt_iter: &mut StmtIter<'a, 'tcx>,
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storage_live_stmts: &mut Vec<(usize, Local)>,
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storage_dead_stmts: &mut Vec<(usize, Local)>,
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) {
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try_eat(stmt_iter, is_storage_stmt, |idx, stmt| {
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if let StatementKind::StorageLive(l) = stmt.kind {
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storage_live_stmts.push((idx, l));
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} else if let StatementKind::StorageDead(l) = stmt.kind {
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storage_dead_stmts.push((idx, l));
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}
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})
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}
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fn is_tmp_storage_stmt<'tcx>(stmt: &Statement<'tcx>) -> bool {
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use rustc_middle::mir::StatementKind::Assign;
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if let Assign(box (place, Rvalue::Use(Operand::Copy(p) | Operand::Move(p)))) = &stmt.kind {
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place.as_local().is_some() && p.as_local().is_some()
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} else {
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false
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}
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}
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/// Eats consecutive `Assign` Statements.
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// The iterator `stmt_iter` is not advanced if none were found.
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fn try_eat_assign_tmp_stmts<'a, 'tcx>(
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stmt_iter: &mut StmtIter<'a, 'tcx>,
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tmp_assigns: &mut Vec<(Local, Local)>,
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nop_stmts: &mut Vec<usize>,
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) {
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try_eat(stmt_iter, is_tmp_storage_stmt, |idx, stmt| {
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use rustc_middle::mir::StatementKind::Assign;
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if let Assign(box (place, Rvalue::Use(Operand::Copy(p) | Operand::Move(p)))) =
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&stmt.kind
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{
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tmp_assigns.push((place.as_local().unwrap(), p.as_local().unwrap()));
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nop_stmts.push(idx);
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}
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})
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}
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fn find_storage_live_dead_stmts_for_local<'tcx>(
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local: Local,
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stmts: &[Statement<'tcx>],
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) -> Option<(usize, usize)> {
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trace!("looking for {:?}", local);
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let mut storage_live_stmt = None;
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let mut storage_dead_stmt = None;
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for (idx, stmt) in stmts.iter().enumerate() {
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if stmt.kind == StatementKind::StorageLive(local) {
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storage_live_stmt = Some(idx);
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} else if stmt.kind == StatementKind::StorageDead(local) {
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storage_dead_stmt = Some(idx);
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}
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}
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Some((storage_live_stmt?, storage_dead_stmt.unwrap_or(usize::MAX)))
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}
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// Try to match the expected MIR structure with the basic block we're processing.
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// We want to see something that looks like:
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// ```
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// (StorageLive(_) | StorageDead(_));*
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// _LOCAL_INTO = ((_LOCAL_FROM as Variant).FIELD: TY);
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// (StorageLive(_) | StorageDead(_));*
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// (tmp_n+1 = tmp_n);*
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// (StorageLive(_) | StorageDead(_));*
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// (tmp_n+1 = tmp_n);*
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// ((LOCAL_FROM as Variant).FIELD: TY) = move tmp;
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// discriminant(LOCAL_FROM) = VariantIdx;
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// (StorageLive(_) | StorageDead(_));*
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// ```
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let mut stmt_iter = stmts.iter().enumerate().peekable();
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try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts);
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let (get_variant_field_stmt, stmt) = stmt_iter.next()?;
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let (local_tmp_s0, local_1, vf_s0, dbg_projection) = match_get_variant_field(stmt)?;
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try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts);
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try_eat_assign_tmp_stmts(&mut stmt_iter, &mut tmp_assigns, &mut nop_stmts);
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try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts);
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try_eat_assign_tmp_stmts(&mut stmt_iter, &mut tmp_assigns, &mut nop_stmts);
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let (idx, stmt) = stmt_iter.next()?;
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let (local_tmp_s1, local_0, vf_s1) = match_set_variant_field(stmt)?;
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nop_stmts.push(idx);
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let (idx, stmt) = stmt_iter.next()?;
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let (set_discr_local, set_discr_var_idx) = match_set_discr(stmt)?;
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let discr_stmt_source_info = stmt.source_info;
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nop_stmts.push(idx);
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try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts);
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for (live_idx, live_local) in storage_live_stmts {
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if let Some(i) = storage_dead_stmts.iter().rposition(|(_, l)| *l == live_local) {
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let (dead_idx, _) = storage_dead_stmts.swap_remove(i);
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storage_stmts.push((live_idx, dead_idx, live_local));
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if live_local == local_tmp_s0 {
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nop_stmts.push(get_variant_field_stmt);
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}
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}
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}
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// We sort primitive usize here so we can use unstable sort
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nop_stmts.sort_unstable();
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// Use one of the statements we're going to discard between the point
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// where the storage location for the variant field becomes live and
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// is killed.
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let (live_idx, dead_idx) = find_storage_live_dead_stmts_for_local(local_tmp_s0, stmts)?;
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let stmt_to_overwrite =
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nop_stmts.iter().find(|stmt_idx| live_idx < **stmt_idx && **stmt_idx < dead_idx);
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let mut tmp_assigned_vars = BitSet::new_empty(locals_count);
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for (l, r) in &tmp_assigns {
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tmp_assigned_vars.insert(*l);
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tmp_assigned_vars.insert(*r);
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}
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let dbg_info_to_adjust: Vec<_> = debug_info
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.iter()
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.enumerate()
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.filter_map(|(i, var_info)| {
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if let VarDebugInfoContents::Place(p) = var_info.value {
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if tmp_assigned_vars.contains(p.local) {
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return Some(i);
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}
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}
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None
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})
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.collect();
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Some(ArmIdentityInfo {
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local_temp_0: local_tmp_s0,
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local_1,
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vf_s0,
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get_variant_field_stmt,
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field_tmp_assignments: tmp_assigns,
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local_tmp_s1,
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local_0,
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vf_s1,
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set_discr_local,
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set_discr_var_idx,
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stmt_to_overwrite: *stmt_to_overwrite?,
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source_info: discr_stmt_source_info,
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storage_stmts,
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stmts_to_remove: nop_stmts,
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dbg_info_to_adjust,
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dbg_projection,
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})
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}
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fn optimization_applies<'tcx>(
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opt_info: &ArmIdentityInfo<'tcx>,
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local_decls: &IndexVec<Local, LocalDecl<'tcx>>,
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local_uses: &IndexVec<Local, usize>,
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var_debug_info: &[VarDebugInfo<'tcx>],
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) -> bool {
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trace!("testing if optimization applies...");
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// FIXME(wesleywiser): possibly relax this restriction?
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if opt_info.local_0 == opt_info.local_1 {
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trace!("NO: moving into ourselves");
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return false;
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} else if opt_info.vf_s0 != opt_info.vf_s1 {
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trace!("NO: the field-and-variant information do not match");
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return false;
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} else if local_decls[opt_info.local_0].ty != local_decls[opt_info.local_1].ty {
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// FIXME(Centril,oli-obk): possibly relax to same layout?
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trace!("NO: source and target locals have different types");
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return false;
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} else if (opt_info.local_0, opt_info.vf_s0.var_idx)
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!= (opt_info.set_discr_local, opt_info.set_discr_var_idx)
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{
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trace!("NO: the discriminants do not match");
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return false;
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}
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// Verify the assignment chain consists of the form b = a; c = b; d = c; etc...
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if opt_info.field_tmp_assignments.is_empty() {
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trace!("NO: no assignments found");
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return false;
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}
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let mut last_assigned_to = opt_info.field_tmp_assignments[0].1;
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let source_local = last_assigned_to;
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for (l, r) in &opt_info.field_tmp_assignments {
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if *r != last_assigned_to {
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trace!("NO: found unexpected assignment {:?} = {:?}", l, r);
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return false;
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}
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last_assigned_to = *l;
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}
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// Check that the first and last used locals are only used twice
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// since they are of the form:
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//
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// ```
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// _first = ((_x as Variant).n: ty);
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// _n = _first;
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// ...
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// ((_y as Variant).n: ty) = _n;
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// discriminant(_y) = z;
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// ```
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for (l, r) in &opt_info.field_tmp_assignments {
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if local_uses[*l] != 2 {
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warn!("NO: FAILED assignment chain local {:?} was used more than twice", l);
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return false;
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} else if local_uses[*r] != 2 {
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warn!("NO: FAILED assignment chain local {:?} was used more than twice", r);
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return false;
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}
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}
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// Check that debug info only points to full Locals and not projections.
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for dbg_idx in &opt_info.dbg_info_to_adjust {
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let dbg_info = &var_debug_info[*dbg_idx];
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if let VarDebugInfoContents::Place(p) = dbg_info.value {
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if !p.projection.is_empty() {
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trace!("NO: debug info for {:?} had a projection {:?}", dbg_info.name, p);
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return false;
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}
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}
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}
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if source_local != opt_info.local_temp_0 {
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trace!(
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"NO: start of assignment chain does not match enum variant temp: {:?} != {:?}",
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source_local,
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opt_info.local_temp_0
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);
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return false;
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} else if last_assigned_to != opt_info.local_tmp_s1 {
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trace!(
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"NO: end of assignemnt chain does not match written enum temp: {:?} != {:?}",
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last_assigned_to,
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opt_info.local_tmp_s1
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);
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return false;
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}
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trace!("SUCCESS: optimization applies!");
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true
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}
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impl<'tcx> MirPass<'tcx> for SimplifyArmIdentity {
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fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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// FIXME(77359): This optimization can result in unsoundness.
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if !tcx.sess.opts.debugging_opts.unsound_mir_opts {
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return;
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}
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let source = body.source;
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trace!("running SimplifyArmIdentity on {:?}", source);
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let local_uses = LocalUseCounter::get_local_uses(body);
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let (basic_blocks, local_decls, debug_info) =
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body.basic_blocks_local_decls_mut_and_var_debug_info();
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for bb in basic_blocks {
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if let Some(opt_info) =
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get_arm_identity_info(&bb.statements, local_decls.len(), debug_info)
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{
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trace!("got opt_info = {:#?}", opt_info);
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if !optimization_applies(&opt_info, local_decls, &local_uses, &debug_info) {
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debug!("optimization skipped for {:?}", source);
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continue;
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}
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// Also remove unused Storage{Live,Dead} statements which correspond
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// to temps used previously.
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for (live_idx, dead_idx, local) in &opt_info.storage_stmts {
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// The temporary that we've read the variant field into is scoped to this block,
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// so we can remove the assignment.
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if *local == opt_info.local_temp_0 {
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bb.statements[opt_info.get_variant_field_stmt].make_nop();
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}
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for (left, right) in &opt_info.field_tmp_assignments {
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if local == left || local == right {
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bb.statements[*live_idx].make_nop();
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bb.statements[*dead_idx].make_nop();
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}
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}
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}
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// Right shape; transform
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for stmt_idx in opt_info.stmts_to_remove {
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bb.statements[stmt_idx].make_nop();
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}
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let stmt = &mut bb.statements[opt_info.stmt_to_overwrite];
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stmt.source_info = opt_info.source_info;
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stmt.kind = StatementKind::Assign(Box::new((
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opt_info.local_0.into(),
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Rvalue::Use(Operand::Move(opt_info.local_1.into())),
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)));
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bb.statements.retain(|stmt| stmt.kind != StatementKind::Nop);
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// Fix the debug info to point to the right local
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for dbg_index in opt_info.dbg_info_to_adjust {
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let dbg_info = &mut debug_info[dbg_index];
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assert!(
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matches!(dbg_info.value, VarDebugInfoContents::Place(_)),
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"value was not a Place"
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);
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if let VarDebugInfoContents::Place(p) = &mut dbg_info.value {
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assert!(p.projection.is_empty());
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p.local = opt_info.local_0;
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p.projection = opt_info.dbg_projection;
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}
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}
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trace!("block is now {:?}", bb.statements);
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}
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}
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}
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}
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struct LocalUseCounter {
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local_uses: IndexVec<Local, usize>,
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}
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impl LocalUseCounter {
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fn get_local_uses<'tcx>(body: &Body<'tcx>) -> IndexVec<Local, usize> {
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let mut counter = LocalUseCounter { local_uses: IndexVec::from_elem(0, &body.local_decls) };
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counter.visit_body(body);
|
|
counter.local_uses
|
|
}
|
|
}
|
|
|
|
impl<'tcx> Visitor<'tcx> for LocalUseCounter {
|
|
fn visit_local(&mut self, local: &Local, context: PlaceContext, _location: Location) {
|
|
if context.is_storage_marker()
|
|
|| context == PlaceContext::NonUse(NonUseContext::VarDebugInfo)
|
|
{
|
|
return;
|
|
}
|
|
|
|
self.local_uses[*local] += 1;
|
|
}
|
|
}
|
|
|
|
/// Match on:
|
|
/// ```rust
|
|
/// _LOCAL_INTO = ((_LOCAL_FROM as Variant).FIELD: TY);
|
|
/// ```
|
|
fn match_get_variant_field<'tcx>(
|
|
stmt: &Statement<'tcx>,
|
|
) -> Option<(Local, Local, VarField<'tcx>, &'tcx List<PlaceElem<'tcx>>)> {
|
|
match &stmt.kind {
|
|
StatementKind::Assign(box (
|
|
place_into,
|
|
Rvalue::Use(Operand::Copy(pf) | Operand::Move(pf)),
|
|
)) => {
|
|
let local_into = place_into.as_local()?;
|
|
let (local_from, vf) = match_variant_field_place(*pf)?;
|
|
Some((local_into, local_from, vf, pf.projection))
|
|
}
|
|
_ => None,
|
|
}
|
|
}
|
|
|
|
/// Match on:
|
|
/// ```rust
|
|
/// ((_LOCAL_FROM as Variant).FIELD: TY) = move _LOCAL_INTO;
|
|
/// ```
|
|
fn match_set_variant_field<'tcx>(stmt: &Statement<'tcx>) -> Option<(Local, Local, VarField<'tcx>)> {
|
|
match &stmt.kind {
|
|
StatementKind::Assign(box (place_from, Rvalue::Use(Operand::Move(place_into)))) => {
|
|
let local_into = place_into.as_local()?;
|
|
let (local_from, vf) = match_variant_field_place(*place_from)?;
|
|
Some((local_into, local_from, vf))
|
|
}
|
|
_ => None,
|
|
}
|
|
}
|
|
|
|
/// Match on:
|
|
/// ```rust
|
|
/// discriminant(_LOCAL_TO_SET) = VAR_IDX;
|
|
/// ```
|
|
fn match_set_discr<'tcx>(stmt: &Statement<'tcx>) -> Option<(Local, VariantIdx)> {
|
|
match &stmt.kind {
|
|
StatementKind::SetDiscriminant { place, variant_index } => {
|
|
Some((place.as_local()?, *variant_index))
|
|
}
|
|
_ => None,
|
|
}
|
|
}
|
|
|
|
#[derive(PartialEq, Debug)]
|
|
struct VarField<'tcx> {
|
|
field: Field,
|
|
field_ty: Ty<'tcx>,
|
|
var_idx: VariantIdx,
|
|
}
|
|
|
|
/// Match on `((_LOCAL as Variant).FIELD: TY)`.
|
|
fn match_variant_field_place<'tcx>(place: Place<'tcx>) -> Option<(Local, VarField<'tcx>)> {
|
|
match place.as_ref() {
|
|
PlaceRef {
|
|
local,
|
|
projection: &[ProjectionElem::Downcast(_, var_idx), ProjectionElem::Field(field, ty)],
|
|
} => Some((local, VarField { field, field_ty: ty, var_idx })),
|
|
_ => None,
|
|
}
|
|
}
|
|
|
|
/// Simplifies `SwitchInt(_) -> [targets]`,
|
|
/// where all the `targets` have the same form,
|
|
/// into `goto -> target_first`.
|
|
pub struct SimplifyBranchSame;
|
|
|
|
impl<'tcx> MirPass<'tcx> for SimplifyBranchSame {
|
|
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
|
|
trace!("Running SimplifyBranchSame on {:?}", body.source);
|
|
let finder = SimplifyBranchSameOptimizationFinder { body, tcx };
|
|
let opts = finder.find();
|
|
|
|
let did_remove_blocks = opts.len() > 0;
|
|
for opt in opts.iter() {
|
|
trace!("SUCCESS: Applying optimization {:?}", opt);
|
|
// Replace `SwitchInt(..) -> [bb_first, ..];` with a `goto -> bb_first;`.
|
|
body.basic_blocks_mut()[opt.bb_to_opt_terminator].terminator_mut().kind =
|
|
TerminatorKind::Goto { target: opt.bb_to_goto };
|
|
}
|
|
|
|
if did_remove_blocks {
|
|
// We have dead blocks now, so remove those.
|
|
simplify::remove_dead_blocks(tcx, body);
|
|
}
|
|
}
|
|
}
|
|
|
|
#[derive(Debug)]
|
|
struct SimplifyBranchSameOptimization {
|
|
/// All basic blocks are equal so go to this one
|
|
bb_to_goto: BasicBlock,
|
|
/// Basic block where the terminator can be simplified to a goto
|
|
bb_to_opt_terminator: BasicBlock,
|
|
}
|
|
|
|
struct SwitchTargetAndValue {
|
|
target: BasicBlock,
|
|
// None in case of the `otherwise` case
|
|
value: Option<u128>,
|
|
}
|
|
|
|
struct SimplifyBranchSameOptimizationFinder<'a, 'tcx> {
|
|
body: &'a Body<'tcx>,
|
|
tcx: TyCtxt<'tcx>,
|
|
}
|
|
|
|
impl<'a, 'tcx> SimplifyBranchSameOptimizationFinder<'a, 'tcx> {
|
|
fn find(&self) -> Vec<SimplifyBranchSameOptimization> {
|
|
self.body
|
|
.basic_blocks()
|
|
.iter_enumerated()
|
|
.filter_map(|(bb_idx, bb)| {
|
|
let (discr_switched_on, targets_and_values) = match &bb.terminator().kind {
|
|
TerminatorKind::SwitchInt { targets, discr, .. } => {
|
|
let targets_and_values: Vec<_> = targets.iter()
|
|
.map(|(val, target)| SwitchTargetAndValue { target, value: Some(val) })
|
|
.chain(once(SwitchTargetAndValue { target: targets.otherwise(), value: None }))
|
|
.collect();
|
|
(discr, targets_and_values)
|
|
},
|
|
_ => return None,
|
|
};
|
|
|
|
// find the adt that has its discriminant read
|
|
// assuming this must be the last statement of the block
|
|
let adt_matched_on = match &bb.statements.last()?.kind {
|
|
StatementKind::Assign(box (place, rhs))
|
|
if Some(*place) == discr_switched_on.place() =>
|
|
{
|
|
match rhs {
|
|
Rvalue::Discriminant(adt_place) if adt_place.ty(self.body, self.tcx).ty.is_enum() => adt_place,
|
|
_ => {
|
|
trace!("NO: expected a discriminant read of an enum instead of: {:?}", rhs);
|
|
return None;
|
|
}
|
|
}
|
|
}
|
|
other => {
|
|
trace!("NO: expected an assignment of a discriminant read to a place. Found: {:?}", other);
|
|
return None
|
|
},
|
|
};
|
|
|
|
let mut iter_bbs_reachable = targets_and_values
|
|
.iter()
|
|
.map(|target_and_value| (target_and_value, &self.body.basic_blocks()[target_and_value.target]))
|
|
.filter(|(_, bb)| {
|
|
// Reaching `unreachable` is UB so assume it doesn't happen.
|
|
bb.terminator().kind != TerminatorKind::Unreachable
|
|
// But `asm!(...)` could abort the program,
|
|
// so we cannot assume that the `unreachable` terminator itself is reachable.
|
|
// FIXME(Centril): use a normalization pass instead of a check.
|
|
|| bb.statements.iter().any(|stmt| matches!(stmt.kind, StatementKind::LlvmInlineAsm(..)))
|
|
})
|
|
.peekable();
|
|
|
|
let bb_first = iter_bbs_reachable.peek().map_or(&targets_and_values[0], |(idx, _)| *idx);
|
|
let mut all_successors_equivalent = StatementEquality::TrivialEqual;
|
|
|
|
// All successor basic blocks must be equal or contain statements that are pairwise considered equal.
|
|
for ((target_and_value_l,bb_l), (target_and_value_r,bb_r)) in iter_bbs_reachable.tuple_windows() {
|
|
let trivial_checks = bb_l.is_cleanup == bb_r.is_cleanup
|
|
&& bb_l.terminator().kind == bb_r.terminator().kind
|
|
&& bb_l.statements.len() == bb_r.statements.len();
|
|
let statement_check = || {
|
|
bb_l.statements.iter().zip(&bb_r.statements).try_fold(StatementEquality::TrivialEqual, |acc,(l,r)| {
|
|
let stmt_equality = self.statement_equality(*adt_matched_on, &l, target_and_value_l, &r, target_and_value_r);
|
|
if matches!(stmt_equality, StatementEquality::NotEqual) {
|
|
// short circuit
|
|
None
|
|
} else {
|
|
Some(acc.combine(&stmt_equality))
|
|
}
|
|
})
|
|
.unwrap_or(StatementEquality::NotEqual)
|
|
};
|
|
if !trivial_checks {
|
|
all_successors_equivalent = StatementEquality::NotEqual;
|
|
break;
|
|
}
|
|
all_successors_equivalent = all_successors_equivalent.combine(&statement_check());
|
|
};
|
|
|
|
match all_successors_equivalent{
|
|
StatementEquality::TrivialEqual => {
|
|
// statements are trivially equal, so just take first
|
|
trace!("Statements are trivially equal");
|
|
Some(SimplifyBranchSameOptimization {
|
|
bb_to_goto: bb_first.target,
|
|
bb_to_opt_terminator: bb_idx,
|
|
})
|
|
}
|
|
StatementEquality::ConsideredEqual(bb_to_choose) => {
|
|
trace!("Statements are considered equal");
|
|
Some(SimplifyBranchSameOptimization {
|
|
bb_to_goto: bb_to_choose,
|
|
bb_to_opt_terminator: bb_idx,
|
|
})
|
|
}
|
|
StatementEquality::NotEqual => {
|
|
trace!("NO: not all successors of basic block {:?} were equivalent", bb_idx);
|
|
None
|
|
}
|
|
}
|
|
})
|
|
.collect()
|
|
}
|
|
|
|
/// Tests if two statements can be considered equal
|
|
///
|
|
/// Statements can be trivially equal if the kinds match.
|
|
/// But they can also be considered equal in the following case A:
|
|
/// ```
|
|
/// discriminant(_0) = 0; // bb1
|
|
/// _0 = move _1; // bb2
|
|
/// ```
|
|
/// In this case the two statements are equal iff
|
|
/// - `_0` is an enum where the variant index 0 is fieldless, and
|
|
/// - bb1 was targeted by a switch where the discriminant of `_1` was switched on
|
|
fn statement_equality(
|
|
&self,
|
|
adt_matched_on: Place<'tcx>,
|
|
x: &Statement<'tcx>,
|
|
x_target_and_value: &SwitchTargetAndValue,
|
|
y: &Statement<'tcx>,
|
|
y_target_and_value: &SwitchTargetAndValue,
|
|
) -> StatementEquality {
|
|
let helper = |rhs: &Rvalue<'tcx>,
|
|
place: &Place<'tcx>,
|
|
variant_index: &VariantIdx,
|
|
switch_value: u128,
|
|
side_to_choose| {
|
|
let place_type = place.ty(self.body, self.tcx).ty;
|
|
let adt = match *place_type.kind() {
|
|
ty::Adt(adt, _) if adt.is_enum() => adt,
|
|
_ => return StatementEquality::NotEqual,
|
|
};
|
|
let variant_discr = adt.discriminant_for_variant(self.tcx, *variant_index).val;
|
|
if variant_discr != switch_value {
|
|
trace!(
|
|
"NO: variant discriminant {} does not equal switch value {}",
|
|
variant_discr,
|
|
switch_value
|
|
);
|
|
return StatementEquality::NotEqual;
|
|
}
|
|
let variant_is_fieldless = adt.variants[*variant_index].fields.is_empty();
|
|
if !variant_is_fieldless {
|
|
trace!("NO: variant {:?} was not fieldless", variant_index);
|
|
return StatementEquality::NotEqual;
|
|
}
|
|
|
|
match rhs {
|
|
Rvalue::Use(operand) if operand.place() == Some(adt_matched_on) => {
|
|
StatementEquality::ConsideredEqual(side_to_choose)
|
|
}
|
|
_ => {
|
|
trace!(
|
|
"NO: RHS of assignment was {:?}, but expected it to match the adt being matched on in the switch, which is {:?}",
|
|
rhs,
|
|
adt_matched_on
|
|
);
|
|
StatementEquality::NotEqual
|
|
}
|
|
}
|
|
};
|
|
match (&x.kind, &y.kind) {
|
|
// trivial case
|
|
(x, y) if x == y => StatementEquality::TrivialEqual,
|
|
|
|
// check for case A
|
|
(
|
|
StatementKind::Assign(box (_, rhs)),
|
|
StatementKind::SetDiscriminant { place, variant_index },
|
|
)
|
|
// we need to make sure that the switch value that targets the bb with SetDiscriminant (y), is the same as the variant index
|
|
if y_target_and_value.value.is_some() => {
|
|
// choose basic block of x, as that has the assign
|
|
helper(rhs, place, variant_index, y_target_and_value.value.unwrap(), x_target_and_value.target)
|
|
}
|
|
(
|
|
StatementKind::SetDiscriminant { place, variant_index },
|
|
StatementKind::Assign(box (_, rhs)),
|
|
)
|
|
// we need to make sure that the switch value that targets the bb with SetDiscriminant (x), is the same as the variant index
|
|
if x_target_and_value.value.is_some() => {
|
|
// choose basic block of y, as that has the assign
|
|
helper(rhs, place, variant_index, x_target_and_value.value.unwrap(), y_target_and_value.target)
|
|
}
|
|
_ => {
|
|
trace!("NO: statements `{:?}` and `{:?}` not considered equal", x, y);
|
|
StatementEquality::NotEqual
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
#[derive(Copy, Clone, Eq, PartialEq)]
|
|
enum StatementEquality {
|
|
/// The two statements are trivially equal; same kind
|
|
TrivialEqual,
|
|
/// The two statements are considered equal, but may be of different kinds. The BasicBlock field is the basic block to jump to when performing the branch-same optimization.
|
|
/// For example, `_0 = _1` and `discriminant(_0) = discriminant(0)` are considered equal if 0 is a fieldless variant of an enum. But we don't want to jump to the basic block with the SetDiscriminant, as that is not legal if _1 is not the 0 variant index
|
|
ConsideredEqual(BasicBlock),
|
|
/// The two statements are not equal
|
|
NotEqual,
|
|
}
|
|
|
|
impl StatementEquality {
|
|
fn combine(&self, other: &StatementEquality) -> StatementEquality {
|
|
use StatementEquality::*;
|
|
match (self, other) {
|
|
(TrivialEqual, TrivialEqual) => TrivialEqual,
|
|
(TrivialEqual, ConsideredEqual(b)) | (ConsideredEqual(b), TrivialEqual) => {
|
|
ConsideredEqual(*b)
|
|
}
|
|
(ConsideredEqual(b1), ConsideredEqual(b2)) => {
|
|
if b1 == b2 {
|
|
ConsideredEqual(*b1)
|
|
} else {
|
|
NotEqual
|
|
}
|
|
}
|
|
(_, NotEqual) | (NotEqual, _) => NotEqual,
|
|
}
|
|
}
|
|
}
|