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Avoid masking shift amounts #1268

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Aug 23, 2022
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Avoid masking shift amounts #1268

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25 changes: 6 additions & 19 deletions src/num.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -150,18 +150,12 @@ pub(crate) fn codegen_int_binop<'tcx>(
BinOp::BitXor => b.bxor(lhs, rhs),
BinOp::BitAnd => b.band(lhs, rhs),
BinOp::BitOr => b.bor(lhs, rhs),
BinOp::Shl => {
let lhs_ty = fx.bcx.func.dfg.value_type(lhs);
let actual_shift = fx.bcx.ins().band_imm(rhs, i64::from(lhs_ty.bits() - 1));
fx.bcx.ins().ishl(lhs, actual_shift)
}
BinOp::Shl => b.ishl(lhs, rhs),
BinOp::Shr => {
let lhs_ty = fx.bcx.func.dfg.value_type(lhs);
let actual_shift = fx.bcx.ins().band_imm(rhs, i64::from(lhs_ty.bits() - 1));
if signed {
fx.bcx.ins().sshr(lhs, actual_shift)
b.sshr(lhs, rhs)
} else {
fx.bcx.ins().ushr(lhs, actual_shift)
b.ushr(lhs, rhs)
}
}
// Compare binops handles by `codegen_binop`.
Expand Down Expand Up @@ -279,22 +273,15 @@ pub(crate) fn codegen_checked_int_binop<'tcx>(
}
}
BinOp::Shl => {
let lhs_ty = fx.bcx.func.dfg.value_type(lhs);
let masked_shift = fx.bcx.ins().band_imm(rhs, i64::from(lhs_ty.bits() - 1));
let val = fx.bcx.ins().ishl(lhs, masked_shift);
let val = fx.bcx.ins().ishl(lhs, rhs);
let ty = fx.bcx.func.dfg.value_type(val);
let max_shift = i64::from(ty.bits()) - 1;
let has_overflow = fx.bcx.ins().icmp_imm(IntCC::UnsignedGreaterThan, rhs, max_shift);
(val, has_overflow)
}
BinOp::Shr => {
let lhs_ty = fx.bcx.func.dfg.value_type(lhs);
let masked_shift = fx.bcx.ins().band_imm(rhs, i64::from(lhs_ty.bits() - 1));
let val = if !signed {
fx.bcx.ins().ushr(lhs, masked_shift)
} else {
fx.bcx.ins().sshr(lhs, masked_shift)
};
let val =
if !signed { fx.bcx.ins().ushr(lhs, rhs) } else { fx.bcx.ins().sshr(lhs, rhs) };
let ty = fx.bcx.func.dfg.value_type(val);
let max_shift = i64::from(ty.bits()) - 1;
let has_overflow = fx.bcx.ins().icmp_imm(IntCC::UnsignedGreaterThan, rhs, max_shift);
Expand Down