[Python-ideas] Disable all peephole optimizations

[Ned Batchelder]

On 5/21/14 8:07 PM, Nick Coghlan wrote:
>
> > Notice that line 6 (the continue) is unreachable, because the 
> else-jump from line 4 has been turned into a jump to bytecode offset 
> 27 (the for loop), and the end of line 5 has also been turned into a 
> jump to 27, rather than letting it flow to line 6.   So line 6 still 
> exists in the bytecode, but is never executed, leading tracing tools 
> to indicate that line 6 is never executed.
>
> So isn't this just a bug in the dead code elimination? Fixing that (so 
> there's no bytecode behind that line and coverage tools can know it 
> has been optimised out) sounds better than adding an obscure config 
> option.
>
Perhaps I don't know how much dead code elimination was intended. 
Assuming we can get to the point that the statement has been completely 
removed, you'll still have the confusing state that a perfectly good 
statement is marked as not executable (because it has no corresponding 
bytecode).  And getting to that point means adding more complexity to 
the bytecode optimizer.
>
> Potentially less risky would be to provide a utility in the dis module 
> to flag such lines after the fact.
>
I don't see how the dis module would know which lines these are?

I'm surprised at the amount of invention and mystery code people will 
propose to avoid having an off-switch for the code we already have.
>
> Cheers,
> Nick.
>