bjoernager/rust
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Implement algebraic simplifications.

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This commit is contained in:
Camille GILLOT 2023-04-15 17:00:43 +00:00
parent 74a967bcec
commit 22986b72e5
5 changed files with 103 additions and 4 deletions
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36
compiler/rustc_mir_transform/src/dataflow_const_prop.rs
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@ -309,7 +309,10 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
) -> (FlatSet<ScalarInt>, FlatSet<bool>) {
let left = self.eval_operand(left, state);
let right = self.eval_operand(right, state);
match (left, right) {
(FlatSet::Bottom, _) | (_, FlatSet::Bottom) => (FlatSet::Bottom, FlatSet::Bottom),
// Both sides are known, do the actual computation.
(FlatSet::Elem(left), FlatSet::Elem(right)) => {
match self.ecx.overflowing_binary_op(op, &left, &right) {
Ok((Scalar::Int(val), overflow, _)) => {
@ -318,11 +321,36 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
_ => (FlatSet::Top, FlatSet::Top),
}
}
(FlatSet::Bottom, _) | (_, FlatSet::Bottom) => (FlatSet::Bottom, FlatSet::Bottom),
(_, _) => {
// Could attempt some algebraic simplifications here.
(FlatSet::Top, FlatSet::Top)
// Exactly one side is known, attempt some algebraic simplifications.
(FlatSet::Elem(const_arg), _) | (_, FlatSet::Elem(const_arg)) => {
let layout = const_arg.layout;
if !matches!(layout.abi, rustc_target::abi::Abi::Scalar(..)) {
return (FlatSet::Top, FlatSet::Top);
}
let arg_scalar = const_arg.to_scalar();
let Ok(arg_scalar) = arg_scalar.try_to_int() else {
return (FlatSet::Top, FlatSet::Top);
};
let Ok(arg_value) = arg_scalar.to_bits(layout.size) else {
return (FlatSet::Top, FlatSet::Top);
};
match op {
BinOp::BitAnd if arg_value == 0 => (FlatSet::Elem(arg_scalar), FlatSet::Bottom),
BinOp::BitOr
if arg_value == layout.size.truncate(u128::MAX)
|| (layout.ty.is_bool() && arg_value == 1) =>
{
(FlatSet::Elem(arg_scalar), FlatSet::Bottom)
}
BinOp::Mul if layout.ty.is_integral() && arg_value == 0 => {
(FlatSet::Elem(arg_scalar), FlatSet::Elem(false))
}
_ => (FlatSet::Top, FlatSet::Top),
}
}
(FlatSet::Top, FlatSet::Top) => (FlatSet::Top, FlatSet::Top),
}
}