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Updating the MIR with MirPatch
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@DianQK
DianQK committed Feb 21, 2024
1 parent f79fd40 commit dec8b9d
Showing 1 changed file with 52 additions and 50 deletions.
102 changes: 52 additions & 50 deletions compiler/rustc_mir_transform/src/match_branches.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
use rustc_index::IndexVec;
use rustc_index::IndexSlice;
use rustc_middle::mir::patch::MirPatch;
use rustc_middle::mir::*;
use rustc_middle::ty::{ParamEnv, ScalarInt, Ty, TyCtxt};
use std::iter;
Expand All @@ -16,9 +17,10 @@ impl<'tcx> MirPass<'tcx> for MatchBranchSimplification {
let def_id = body.source.def_id();
let param_env = tcx.param_env_reveal_all_normalized(def_id);

let bbs = body.basic_blocks.as_mut();
let mut should_cleanup = false;
for bb_idx in bbs.indices() {
for i in 0..body.basic_blocks.len() {
let bbs = &*body.basic_blocks;
let bb_idx = BasicBlock::from_usize(i);
if !tcx.consider_optimizing(|| format!("MatchBranchSimplification {def_id:?} ")) {
continue;
}
Expand All @@ -34,12 +36,11 @@ impl<'tcx> MirPass<'tcx> for MatchBranchSimplification {
_ => continue,
};

if SimplifyToIf.simplify(tcx, &mut body.local_decls, bbs, bb_idx, param_env) {
if SimplifyToIf.simplify(tcx, body, bb_idx, param_env) {
should_cleanup = true;
continue;
}
if SimplifyToExp::default().simplify(tcx, &mut body.local_decls, bbs, bb_idx, param_env)
{
if SimplifyToExp::default().simplify(tcx, body, bb_idx, param_env) {
should_cleanup = true;
continue;
}
Expand All @@ -57,43 +58,42 @@ trait SimplifyMatch<'tcx> {
fn simplify(
&mut self,
tcx: TyCtxt<'tcx>,
local_decls: &mut IndexVec<Local, LocalDecl<'tcx>>,
bbs: &mut IndexVec<BasicBlock, BasicBlockData<'tcx>>,
body: &mut Body<'tcx>,
switch_bb_idx: BasicBlock,
param_env: ParamEnv<'tcx>,
) -> bool {
let bbs = &body.basic_blocks;
let (discr, targets) = match bbs[switch_bb_idx].terminator().kind {
TerminatorKind::SwitchInt { ref discr, ref targets, .. } => (discr, targets),
_ => unreachable!(),
};

let discr_ty = discr.ty(local_decls, tcx);
// let local_decls = body.local_decls();
let discr_ty = discr.ty(body.local_decls(), tcx);
if !self.can_simplify(tcx, targets, param_env, bbs, discr_ty) {
return false;
}

let mut patch = MirPatch::new(body);

// Take ownership of items now that we know we can optimize.
let discr = discr.clone();

// Introduce a temporary for the discriminant value.
let source_info = bbs[switch_bb_idx].terminator().source_info;
let discr_local = local_decls.push(LocalDecl::new(discr_ty, source_info.span));
let discr_local = patch.new_temp(discr_ty, source_info.span);

// We already checked that targets are different blocks,
// and bb_idx has a different terminator from both of them.
let new_stmts = self.new_stmts(tcx, targets, param_env, bbs, discr_local, discr_ty);
let (_, first) = targets.iter().next().unwrap();
let (from, first) = bbs.pick2_mut(switch_bb_idx, first);
from.statements
.push(Statement { source_info, kind: StatementKind::StorageLive(discr_local) });
from.statements.push(Statement {
source_info,
kind: StatementKind::Assign(Box::new((Place::from(discr_local), Rvalue::Use(discr)))),
});
from.statements.extend(new_stmts);
from.statements
.push(Statement { source_info, kind: StatementKind::StorageDead(discr_local) });
from.terminator_mut().kind = first.terminator().kind.clone();
let statement_index = bbs[switch_bb_idx].statements.len();
let parent_end = Location { block: switch_bb_idx, statement_index };
patch.add_statement(parent_end, StatementKind::StorageLive(discr_local));
patch.add_assign(parent_end, Place::from(discr_local), Rvalue::Use(discr));
self.new_stmts(tcx, targets, param_env, &mut patch, parent_end, bbs, discr_local, discr_ty);
patch.add_statement(parent_end, StatementKind::StorageDead(discr_local));
patch.patch_terminator(switch_bb_idx, bbs[first].terminator().kind.clone());
patch.apply(body);
true
}

Expand All @@ -102,7 +102,7 @@ trait SimplifyMatch<'tcx> {
tcx: TyCtxt<'tcx>,
targets: &SwitchTargets,
param_env: ParamEnv<'tcx>,
bbs: &IndexVec<BasicBlock, BasicBlockData<'tcx>>,
bbs: &IndexSlice<BasicBlock, BasicBlockData<'tcx>>,
discr_ty: Ty<'tcx>,
) -> bool;

Expand All @@ -111,10 +111,12 @@ trait SimplifyMatch<'tcx> {
tcx: TyCtxt<'tcx>,
targets: &SwitchTargets,
param_env: ParamEnv<'tcx>,
bbs: &IndexVec<BasicBlock, BasicBlockData<'tcx>>,
patch: &mut MirPatch<'tcx>,
parent_end: Location,
bbs: &IndexSlice<BasicBlock, BasicBlockData<'tcx>>,
discr_local: Local,
discr_ty: Ty<'tcx>,
) -> Vec<Statement<'tcx>>;
);
}

struct SimplifyToIf;
Expand Down Expand Up @@ -156,7 +158,7 @@ impl<'tcx> SimplifyMatch<'tcx> for SimplifyToIf {
tcx: TyCtxt<'tcx>,
targets: &SwitchTargets,
param_env: ParamEnv<'tcx>,
bbs: &IndexVec<BasicBlock, BasicBlockData<'tcx>>,
bbs: &IndexSlice<BasicBlock, BasicBlockData<'tcx>>,
_discr_ty: Ty<'tcx>,
) -> bool {
if targets.iter().len() != 1 {
Expand Down Expand Up @@ -207,20 +209,23 @@ impl<'tcx> SimplifyMatch<'tcx> for SimplifyToIf {
tcx: TyCtxt<'tcx>,
targets: &SwitchTargets,
param_env: ParamEnv<'tcx>,
bbs: &IndexVec<BasicBlock, BasicBlockData<'tcx>>,
patch: &mut MirPatch<'tcx>,
parent_end: Location,
bbs: &IndexSlice<BasicBlock, BasicBlockData<'tcx>>,
discr_local: Local,
discr_ty: Ty<'tcx>,
) -> Vec<Statement<'tcx>> {
) {
let (val, first) = targets.iter().next().unwrap();
let second = targets.otherwise();
// We already checked that first and second are different blocks,
// and bb_idx has a different terminator from both of them.
let first = &bbs[first];
let second = &bbs[second];

let new_stmts = iter::zip(&first.statements, &second.statements).map(|(f, s)| {
for (f, s) in iter::zip(&first.statements, &second.statements) {
match (&f.kind, &s.kind) {
(f_s, s_s) if f_s == s_s => (*f).clone(),
(f_s, s_s) if f_s == s_s => {
patch.add_statement(parent_end, f.kind.clone());
}

(
StatementKind::Assign(box (lhs, Rvalue::Use(Operand::Constant(f_c)))),
Expand All @@ -231,7 +236,7 @@ impl<'tcx> SimplifyMatch<'tcx> for SimplifyToIf {
let s_b = s_c.const_.try_eval_bool(tcx, param_env).unwrap();
if f_b == s_b {
// Same value in both blocks. Use statement as is.
(*f).clone()
patch.add_statement(parent_end, f.kind.clone());
} else {
// Different value between blocks. Make value conditional on switch condition.
let size = tcx.layout_of(param_env.and(discr_ty)).unwrap().size;
Expand All @@ -246,17 +251,13 @@ impl<'tcx> SimplifyMatch<'tcx> for SimplifyToIf {
op,
Box::new((Operand::Copy(Place::from(discr_local)), const_cmp)),
);
Statement {
source_info: f.source_info,
kind: StatementKind::Assign(Box::new((*lhs, rhs))),
}
patch.add_assign(parent_end, *lhs, rhs);
}
}

_ => unreachable!(),
}
});
new_stmts.collect()
}
}
}

Expand Down Expand Up @@ -333,7 +334,7 @@ impl<'tcx> SimplifyMatch<'tcx> for SimplifyToExp {
tcx: TyCtxt<'tcx>,
targets: &SwitchTargets,
param_env: ParamEnv<'tcx>,
bbs: &IndexVec<BasicBlock, BasicBlockData<'tcx>>,
bbs: &IndexSlice<BasicBlock, BasicBlockData<'tcx>>,
discr_ty: Ty<'tcx>,
) -> bool {
if targets.iter().len() < 2 || targets.iter().len() > 64 {
Expand Down Expand Up @@ -467,16 +468,20 @@ impl<'tcx> SimplifyMatch<'tcx> for SimplifyToExp {
_tcx: TyCtxt<'tcx>,
targets: &SwitchTargets,
_param_env: ParamEnv<'tcx>,
bbs: &IndexVec<BasicBlock, BasicBlockData<'tcx>>,
patch: &mut MirPatch<'tcx>,
parent_end: Location,
bbs: &IndexSlice<BasicBlock, BasicBlockData<'tcx>>,
discr_local: Local,
discr_ty: Ty<'tcx>,
) -> Vec<Statement<'tcx>> {
) {
let (_, first) = targets.iter().next().unwrap();
let first = &bbs[first];

let new_stmts =
iter::zip(&self.transfrom_types, &first.statements).map(|(t, s)| match (t, &s.kind) {
(TransfromType::Same, _) | (TransfromType::Eq, _) => (*s).clone(),
for (t, s) in iter::zip(&self.transfrom_types, &first.statements) {
match (t, &s.kind) {
(TransfromType::Same, _) | (TransfromType::Eq, _) => {
patch.add_statement(parent_end, s.kind.clone());
}
(
TransfromType::Discr,
StatementKind::Assign(box (lhs, Rvalue::Use(Operand::Constant(f_c)))),
Expand All @@ -487,13 +492,10 @@ impl<'tcx> SimplifyMatch<'tcx> for SimplifyToExp {
} else {
Rvalue::Cast(CastKind::IntToInt, operand, f_c.const_.ty())
};
Statement {
source_info: s.source_info,
kind: StatementKind::Assign(Box::new((*lhs, r_val))),
}
patch.add_assign(parent_end, *lhs, r_val);
}
_ => unreachable!(),
});
new_stmts.collect()
}
}
}
}

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