snap_usedef and upvalues

[XmiliaH]

In some circumstances snap_usedef can flag a slot as dead, however, a potential upvalue could require it as can be seen in the following example:

-- require"jit".off()

local function f(make_up, when)
    local uv, uvf
    if make_up then
        uvf = function() return uv end
    end
    for i = 1, 1000 do
        if i == when then
            uv = "This"
            if i == 0 then end
            string.gsub("", "", {}) -- Force stich
            return uvf
        end
    end
    error("Not here")
end

f(false, 57)
local uvf = f(true, 1)
print(uvf())

The output should be This and not nil as the only to exit f is with the return and uv is previously set. However, snap_usedef will determine that uv is dead, since at the time of compilation no open upvalue exists for uv.

[MikePall]

Fixed. Thanks!