usual_conversions
ctype = usual_conversions(expr->op, expr->left, expr->right,
ctype = usual_conversions('?', *cond, expr->cond_false,
target = usual_conversions(op, expr->left, expr->right,
ctype = usual_conversions(expr->op, old, zero,
ltype = usual_conversions(op, expr->left, expr->right,