Converting a float/double to unsigned int is undefined if the result
would be negative if converting to a signed int.
x86-64 and arm treat this condition differently---x86-64 returns a value
whose bit pattern is the same as the bit pattern for converting to
signed int, and arm returns zero. So it would be nice to have a warning
that this will (or could) happen.
I couldn't find such a warning in the GCC manual or in the GCC code
base. Looking through the code, it seemed it might go in this code in
force_operand() in expr.c on mainline:
if (UNARY_P (value))
{
if (!target)
target = gen_reg_rtx (GET_MODE (value));
op1 = force_operand (XEXP (value, 0), NULL_RTX);
switch (code)
{
case ZERO_EXTEND:
case SIGN_EXTEND:
case TRUNCATE:
case FLOAT_EXTEND:
case FLOAT_TRUNCATE:
convert_move (target, op1, code == ZERO_EXTEND);
return target;
case FIX:
case UNSIGNED_FIX:
expand_fix (target, op1, code == UNSIGNED_FIX);
return target;
case FLOAT:
case UNSIGNED_FLOAT:
expand_float (target, op1, code == UNSIGNED_FLOAT);
return target;
default:
return expand_simple_unop (GET_MODE (value), code, op1,
target, 0);
}
}
But maybe not.
Any advice on how to proceed? I'd be willing to write and test the few
lines of code myself if I knew where to put them.
Brad
