objdump very long run time when using -D -z flags

[Alan Modra]

On Thu, Apr 30, 2020 at 06:22:11PM -0700, Fangrui Song wrote:
> This just hides the problem.

That isn't true.

> -z is still going to be slow.

Well, yes, because objdump is going to be showing many instructions.

> To avoid
> the quadratic behavior, we should increase the address by at least `z`
> if we have scanned `z` zeros.

What quadratic behaviour related to blocks of zeros?  With -z we now
won't scan, and without -z the entire block (or almost) is consumed.

-- 
Alan Modra
Australia Development Lab, IBM