OpenEuphoria

2. Re: Phix : loop question for Pete

• Posted by petelomax Feb 26, 2018
• 1406 views

Yes, unfortunately I had to.

25/10/2017  An "illegal/unsupported construct" error now occurs if an end  
            for statement is immediately preceded by an unconditional exit. 
            Where possible, use a simple if construct instead. This proved  
            necessary because the opEndFor was being skipped, but that sets  
            the zero iterations jump. Example: 
                for i=1 to length(s) do 
                    ?s[i] 
                    exit 
                end for 
            (s[1] errored on length(s)=0, because the <1 jump was wrong.) 
            However this sort of thing is (still) fine: 
                for i=1 to length(s) do 
                    ?s[i] 
                    if "abc"="def" then 
                        ?"what??" 
                    else 
                        exit 
                    end if 
                end for 
            (assuming the compiler does not optimise that test away too) 
            Update: Problem resurfaced. There are now fixes for this in  
            both pmain.e/DoFor() and pilx86.e/jskip(). 

Feel free to try and improve this. I've tried and failed on at least three occasions, perhaps a fresh perspective would help.

What happens is that the code in pilx86.e line 10787

-- finally, batchpatch zero-iteration jmp(s) [if any] at loop start: 

is not executed, if an unconditional exit causes the opEndFor to be skipped. Note that error can also happen for some always-true cases such as if DEBUG then exit end if.

Perhaps opEndFor could/should be split into opEndFor and opPatchForStart, with the latter not being skipped by an unconditional exit, i.e. that new opcode emitted after the final "backpatch(exitBP,..)" in pmain.e/DoFor().
[I don't think that I actually tried, or previously thought of doing that...]

Pete