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Auto merge of #108282 - cjgillot:mir-checked-sh, r=tmiasko

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Implement checked Shl/Shr at MIR building.

This does not require any special handling by codegen backends,
as the overflow behaviour is entirely determined by the rhs (shift amount).

This allows MIR ConstProp to remove the overflow check for constant shifts.

~There is an existing different behaviour between cg_llvm and cg_clif (cc `@bjorn3).`
I took cg_llvm's one as reference: overflow if `rhs < 0 || rhs > number_of_bits_in_lhs_ty`.~

EDIT: `cg_llvm` and `cg_clif` implement the overflow check differently. This PR uses `cg_llvm`'s implementation based on a `BitAnd` instead of `cg_clif`'s one based on an unsigned comparison.
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bors 2023-03-15 21:31:06 +00:00
commit c90eb4825a
8 changed files with 109 additions and 111 deletions
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4
compiler/rustc_middle/src/mir/syntax.rs
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@ -1083,10 +1083,6 @@ pub enum Rvalue<'tcx> {
/// For addition, subtraction, and multiplication on integers the error condition is set when
/// the infinite precision result would be unequal to the actual result.
///
/// For shift operations on integers the error condition is set when the value of right-hand
/// side is greater than or equal to the number of bits in the type of the left-hand side, or
/// when the value of right-hand side is negative.
///
/// Other combinations of types and operators are unsupported.
CheckedBinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>),