Re: [PATCH] fix jump-misses-init warnings

[Ken Raeburn]

On Sep 14, 2009, at 03:37, Ludovic Courtès wrote:
> Why does it help to move locals to the enclosing scope?  I’d expect  
> the
> opposite.

Jumping over the initializer is a simpler analysis than used-before- 
set.  It may also yield different results, if the "goto" that branches  
into the block and bypasses the initializer can now be reached through  
a path that retains a value of the variable in question stored by a  
previous pass through that block entering at the top.  You could still  
warn "possibly used before set", unless that's the only way to get to  
that goto statement.

If the logic of the function requires recalculating the value on any  
entry to the block, moving the declaration to an outer block is just  
masking the bug, not fixing it.

In this case, though, nothing after the label uses the value of the  
variable for which the initialization is bypassed, so it seems okay.   
Though, I'd think the declaration could be left in the same scope, and  
just split into a declaration without initializer and a separate  
assignment statement; that would probably suppress the warning without  
triggering a used-before-set warning, and wouldn't require renaming  
all the other "n" variables.  (If it doesn't, I think it might be a  
smaller change to rename the variable for which the declaration is  
being moved, rather than all the others.)

Ken