Function insert_fcvt_sequence

cranelift/fuzzgen/src/passes/fcvt.rs:67–98

Prepend instructions to inst to avoid traps

(pos: &mut FuncCursor, inst: Inst)

/// Prepend instructions to inst to avoid traps
fn insert_fcvt_sequence(pos: &mut FuncCursor, inst: Inst) {
    let dfg = &pos.func.dfg;
    let opcode = dfg.insts[inst].opcode();
    let arg = dfg.inst_args(inst)[0];
    let float_ty = dfg.value_type(arg);
    let int_ty = dfg.value_type(dfg.first_result(inst));

    // These instructions trap on NaN
    let is_nan = pos.ins().fcmp(FloatCC::NotEqual, arg, arg);

    // They also trap if the value is larger or smaller than what the integer type can represent. So
    // we generate the maximum and minimum float value that would make this trap, and compare against
    // those limits.
    let is_signed = opcode == Opcode::FcvtToSint;
    let (min, max) = float_limits(pos, float_ty, int_ty, is_signed);
    let underflows = pos.ins().fcmp(FloatCC::LessThanOrEqual, arg, min);
    let overflows = pos.ins().fcmp(FloatCC::GreaterThanOrEqual, arg, max);

    // Check the previous conditions and replace with a 1.0 if this instruction would trap
    let overflows_int = pos.ins().bor(underflows, overflows);
    let is_invalid = pos.ins().bor(is_nan, overflows_int);

    let one = if float_ty == F32 {
        pos.ins().f32const(1.0)
    } else {
        pos.ins().f64const(1.0)
    };
    let new_arg = pos.ins().select(is_invalid, one, arg);

    // Replace the previous arg with the new one
    pos.func.dfg.inst_args_mut(inst)[0] = new_arg;
}