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Clean up fragile checks of optimized away constants

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This commit is contained in:
Santiago Pastorino 2020-04-17 18:31:21 -03:00
parent f925a03ead
commit 25e0be736c
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GPG Key ID: 8131A24E0C79EFAF
1 changed files with 10 additions and 25 deletions
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35
src/librustc_mir/transform/simplify.rs
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@ -32,7 +32,7 @@ use rustc_index::bit_set::BitSet;
use rustc_index::vec::{Idx, IndexVec};
use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
use rustc_middle::ty::{self, TyCtxt};
use rustc_middle::ty::TyCtxt;
use std::borrow::Cow;
pub struct SimplifyCfg {
@ -400,33 +400,18 @@ impl<'a, 'tcx> Visitor<'tcx> for DeclMarker<'a, 'tcx> {
if location.statement_index != block.statements.len() {
let stmt = &block.statements[location.statement_index];
fn can_skip_constant(c: &ty::Const<'tcx>) -> bool {
// Keep assignments from unevaluated constants around, since the
// evaluation may report errors, even if the use of the constant
// is dead code.
!matches!(c.val, ty::ConstKind::Unevaluated(..))
}
fn can_skip_operand(o: &Operand<'_>) -> bool {
match o {
Operand::Copy(_) | Operand::Move(_) => true,
Operand::Constant(c) => can_skip_constant(c.literal),
}
}
if let StatementKind::Assign(box (dest, rvalue)) = &stmt.kind {
if !dest.is_indirect() && dest.local == *local {
let can_skip = match rvalue {
Rvalue::Use(op) => can_skip_operand(op),
Rvalue::Discriminant(_) => true,
Rvalue::BinaryOp(_, l, r) | Rvalue::CheckedBinaryOp(_, l, r) => {
can_skip_operand(l) && can_skip_operand(r)
}
Rvalue::Repeat(op, c) => can_skip_operand(op) && can_skip_constant(c),
Rvalue::AddressOf(_, _) => true,
Rvalue::Len(_) => true,
Rvalue::UnaryOp(_, op) => can_skip_operand(op),
Rvalue::Aggregate(_, operands) => operands.iter().all(can_skip_operand),
Rvalue::Use(_)
| Rvalue::Discriminant(_)
| Rvalue::BinaryOp(_, _, _)
| Rvalue::CheckedBinaryOp(_, _, _)
| Rvalue::Repeat(_, _)
| Rvalue::AddressOf(_, _)
| Rvalue::Len(_)
| Rvalue::UnaryOp(_, _)
| Rvalue::Aggregate(_, _) => true,
_ => false,
};