The radical「丷」is a component form of「八」. As mentioned in the other answers, radicals are a way of indexing characters only - their presence does not imply that the radical is part of the Kanji's history or provide any function to the Kanji at all, and there is no contribution of meaning of「丷」towards「前」,「咲」,「呼」. Note that their radicals (section headers in dictionaries) are:
However, calling all appearances of「丷」as component forms of「八」, especially in non-radical contexts, is very dubious. Characters which originally contained「丷」were almost universally turned into「八」in the Kangxi Dictionary printed form of characters, possibly for aesthetic purposes, whereas before they were kept separate. Since most modern Chinese character dictionaries inherit Kangxi radicals, the confusion continues to this day. As far as I can recall, the only semantic contribution of the component「八」(to split, now written「別」) is towards the common characters「半」(half) and「分」(divide).
So, where did「丷」come from in each of「前」,「咲」,「呼」?
In「前」,「丷」is part of「䒑」, which was an abbreviation of「止」. See Why does 前 mean "past" in terms of time, but "forward" in terms of direction? for an explanation for the glyph origin of「前」.
In「咲」,「丷」is also part of「䒑」, but this time「䒑」is a cursive calligraphic variant form of「艸/艹」, the grass/plant component.
「咲」was originally a variant of「笑/㗛」(smile/laughter/happy; the Japanese usage bloom/blossom is a repurposed usage unrelated to the original).「笑」in turn was originally「𦬫」, that is, a combination of grass/plants「艹」and dog「犬」.
For reference,「犬」around the same time period/state looked like:
The forms「咲」and「笑/㗛」came from the oft-muddled component exchange between「艹」and「竹/𥫗」(see What is the character etymology of 着 ? for a model case study) because「艹」and「𥫗」were so similar in shape. In some script styles, they were almost just upside-down versions of each other:
「呼」(to call out) was originally「乎」, which was a picture of a tree branch being blown around in strong winds. The wind was represented by several strokes in an abstract manner.
The character invokes the meaning of howling winds, extended to mean to yell/call out, and「口」was added to emphasise this meaning while the original character「乎」became increasingly used as a Classical Chinese particle. A decorative stroke was added to the top later, resulting in
which leads on to the modern shape.