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interpret: don't rely on ScalarPair for overflowed arithmetic #98627

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merged 2 commits into from
Jul 4, 2022
Merged

interpret: don't rely on ScalarPair for overflowed arithmetic #98627

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interpret: don't rely on ScalarPair for overflowed arithmetic
RalfJung Jun 28, 2022
0850bad
extra assertion, extra sure
RalfJung Jul 4, 2022
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18 changes: 16 additions & 2 deletions compiler/rustc_const_eval/src/interpret/operator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ use rustc_middle::mir;
use rustc_middle::mir::interpret::{InterpResult, Scalar};
use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
use rustc_middle::ty::{self, FloatTy, Ty};
use rustc_target::abi::Abi;

use super::{ImmTy, Immediate, InterpCx, Machine, PlaceTy};

Expand All @@ -25,8 +26,21 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
"type mismatch for result of {:?}",
op,
);
let val = Immediate::ScalarPair(val.into(), Scalar::from_bool(overflowed).into());
self.write_immediate(val, dest)
if let Abi::ScalarPair(..) = dest.layout.abi {
// We can use the optimized path and avoid `place_field` (which might do
// `force_allocation`).
let pair = Immediate::ScalarPair(val.into(), Scalar::from_bool(overflowed).into());
self.write_immediate(pair, dest)?;
} else {
// With randomized layout, `(int, bool)` might cease to be a `ScalarPair`, so we have to
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maybe explicitly assert that we're using -Zrandomize-layout (or however the flag is called) here?

// do a component-wise write here. This code path is slower than the above because
// `place_field` will have to `force_allocate` locals here.
let val_field = self.place_field(&dest, 0)?;
self.write_scalar(val, &val_field)?;
let overflowed_field = self.place_field(&dest, 1)?;
self.write_scalar(Scalar::from_bool(overflowed), &overflowed_field)?;
}
Ok(())
}

/// Applies the binary operation `op` to the arguments and writes the result to the
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