[Bug]: USR call is removed by optimizer

[oskostenko]

Contact Details

No response

Compiler version

v1.18.4

What happened?

sub DoSomething
    print "YES"
end sub

a = usr(@DoSomething)

When compiled with the default optimization level, this program prints nothing, while it is expected to print YES.

The compiler's optimizer detects the value assigned to the variable a is unused and removes the whole instruction, including the usr call. However, usr is not a pure function so it must not be removed by optimizer.

Workaround: instead of usr write your own sub like this:

sub fastcall Call(address as uinteger)
    asm
        jp (hl)
    end asm
end sub

Call @DoSomething

Error and Warning messages

warning: [W150] Variable 'a' is never used

Code of Conduct

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[NMMT76]

I actually have the same issue when writing example code for my EdgeMaster virtual device, as sometimes i have to perform IN's just to flush the buffer or move the buffer forward and i have to either:

• use -01 thus loosing optimizations so i can do tempvar=IN x, or
• use -02/3 and do something pointless like tempvar = IN x : tempvar=tempvar+1 (or similar)

My best suggestion would be something like a discard:

discard = IN/USR/etc

This would be the "best of all worlds" as it signals the compiler we very much want the right side to happen but we don't want it to store the result to any variable at all thus also saving a memory write.

[oskostenko]

Yes, that would be useful. Even better, in my opinion, would be to allow to omit the assignment part at all. User-defined functions are allowed to be called without assignment, like subs. Why the built-in functions cannot be called the same way?

With that said, it's still a bug. The optimizer must not break things. It can remove the unused variable, but it must retain the call if it may have side-effects.