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interpret: simplify handling of shifts by no longer trying to handle signed and unsigned shift amounts in the same branch

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This commit is contained in:
Ralf Jung 2023-11-12 12:16:41 +01:00
parent a04d56b36d
commit 31493c70fa
7 changed files with 86 additions and 58 deletions
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9
compiler/rustc_mir_build/src/build/expr/as_rvalue.rs
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@ -600,10 +600,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
BinOp::Shl | BinOp::Shr if self.check_overflow && ty.is_integral() => {
// For an unsigned RHS, the shift is in-range for `rhs < bits`.
// For a signed RHS, `IntToInt` cast to the equivalent unsigned
// type and do that same comparison. Because the type is the
// same size, there's no negative shift amount that ends up
// overlapping with valid ones, thus it catches negatives too.
// type and do that same comparison.
// A negative value will be *at least* 128 after the cast (that's i8::MIN),
// and 128 is an overflowing shift amount for all our currently existing types,
// so this cast can never make us miss an overflow.
let (lhs_size, _) = ty.int_size_and_signed(self.tcx);
assert!(lhs_size.bits() <= 128);
let rhs_ty = rhs.ty(&self.local_decls, self.tcx);
let (rhs_size, _) = rhs_ty.int_size_and_signed(self.tcx);
@ -625,7 +627,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// This can't overflow because the largest shiftable types are 128-bit,
// which fits in `u8`, the smallest possible `unsigned_ty`.
// (And `from_uint` will `bug!` if that's ever no longer true.)
let lhs_bits = Operand::const_from_scalar(
self.tcx,
unsigned_ty,