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Implement algebraic simplifications.
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@ -309,7 +309,10 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
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) -> (FlatSet<ScalarInt>, FlatSet<bool>) {
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let left = self.eval_operand(left, state);
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let right = self.eval_operand(right, state);
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match (left, right) {
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(FlatSet::Bottom, _) | (_, FlatSet::Bottom) => (FlatSet::Bottom, FlatSet::Bottom),
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// Both sides are known, do the actual computation.
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(FlatSet::Elem(left), FlatSet::Elem(right)) => {
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match self.ecx.overflowing_binary_op(op, &left, &right) {
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Ok((Scalar::Int(val), overflow, _)) => {
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@ -318,11 +321,36 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
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_ => (FlatSet::Top, FlatSet::Top),
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}
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}
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(FlatSet::Bottom, _) | (_, FlatSet::Bottom) => (FlatSet::Bottom, FlatSet::Bottom),
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(_, _) => {
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// Could attempt some algebraic simplifications here.
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(FlatSet::Top, FlatSet::Top)
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// Exactly one side is known, attempt some algebraic simplifications.
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(FlatSet::Elem(const_arg), _) | (_, FlatSet::Elem(const_arg)) => {
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let layout = const_arg.layout;
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if !matches!(layout.abi, rustc_target::abi::Abi::Scalar(..)) {
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return (FlatSet::Top, FlatSet::Top);
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}
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let arg_scalar = const_arg.to_scalar();
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let Ok(arg_scalar) = arg_scalar.try_to_int() else {
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return (FlatSet::Top, FlatSet::Top);
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};
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let Ok(arg_value) = arg_scalar.to_bits(layout.size) else {
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return (FlatSet::Top, FlatSet::Top);
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};
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match op {
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BinOp::BitAnd if arg_value == 0 => (FlatSet::Elem(arg_scalar), FlatSet::Bottom),
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BinOp::BitOr
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if arg_value == layout.size.truncate(u128::MAX)
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|| (layout.ty.is_bool() && arg_value == 1) =>
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{
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(FlatSet::Elem(arg_scalar), FlatSet::Bottom)
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}
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BinOp::Mul if layout.ty.is_integral() && arg_value == 0 => {
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(FlatSet::Elem(arg_scalar), FlatSet::Elem(false))
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}
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_ => (FlatSet::Top, FlatSet::Top),
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}
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}
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(FlatSet::Top, FlatSet::Top) => (FlatSet::Top, FlatSet::Top),
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}
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}
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10
tests/mir-opt/dataflow-const-prop/boolean_identities.rs
Normal file
10
tests/mir-opt/dataflow-const-prop/boolean_identities.rs
Normal file
@ -0,0 +1,10 @@
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// unit-test: DataflowConstProp
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// EMIT_MIR boolean_identities.test.DataflowConstProp.diff
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pub fn test(x: bool, y: bool) -> bool {
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(y | true) & (x & false)
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}
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fn main() {
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test(true, false);
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}
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@ -0,0 +1,33 @@
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- // MIR for `test` before DataflowConstProp
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+ // MIR for `test` after DataflowConstProp
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fn test(_1: bool, _2: bool) -> bool {
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debug x => _1;
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debug y => _2;
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let mut _0: bool;
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let mut _3: bool;
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let mut _4: bool;
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let mut _5: bool;
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let mut _6: bool;
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bb0: {
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StorageLive(_3);
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StorageLive(_4);
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_4 = _2;
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- _3 = BitOr(move _4, const true);
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+ _3 = const true;
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StorageDead(_4);
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StorageLive(_5);
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StorageLive(_6);
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_6 = _1;
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- _5 = BitAnd(move _6, const false);
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+ _5 = const false;
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StorageDead(_6);
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- _0 = BitAnd(move _3, move _5);
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+ _0 = const false;
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StorageDead(_5);
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StorageDead(_3);
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return;
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}
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}
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10
tests/mir-opt/dataflow-const-prop/mult_by_zero.rs
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10
tests/mir-opt/dataflow-const-prop/mult_by_zero.rs
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@ -0,0 +1,10 @@
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// unit-test: DataflowConstProp
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// EMIT_MIR mult_by_zero.test.DataflowConstProp.diff
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fn test(x : i32) -> i32 {
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x * 0
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}
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fn main() {
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test(10);
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}
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@ -0,0 +1,18 @@
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- // MIR for `test` before DataflowConstProp
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+ // MIR for `test` after DataflowConstProp
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fn test(_1: i32) -> i32 {
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debug x => _1;
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let mut _0: i32;
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let mut _2: i32;
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bb0: {
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StorageLive(_2);
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_2 = _1;
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- _0 = Mul(move _2, const 0_i32);
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+ _0 = const 0_i32;
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StorageDead(_2);
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return;
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}
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}
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