Re: [PATCH 5/7] gdb: update blockvector::lookup to handle non-contiguous blocks

[Tom Tromey <tom@tromey.com>]

>>>>> "Jan" == Jan Vrany <jan.vrany@labware.com> writes:

Jan> This commit updates blockvector::lookup to handle non-contiguous without
Jan> help of addrmap. It introduces a new method, block::contains(CORE_ADDR),
Jan> to check whether given block contains given address. This new method is
Jan> then used in blockvector::lookup instead of simply using block's
Jan> start and end addresses.

Jan> A unit test for non-contiguous blocks will come later in this series.

Jan> On Debian x86_64 I see no regressions except

Jan>     FAIL: gdb.dwarf2/debug-names.exp: print _start

Jan> This is caused by discrepancy between the debug info and the debug names
Jan> and will be eventually fixed in a separate patch.

I glossed over this before but is this patch in this series?

Jan> +bool
Jan> +block::contains (const CORE_ADDR addr) const
Jan> +{
Jan> +  if (addr >= start () && addr < end ())
Jan> +    {
Jan> +      if (is_contiguous ())
Jan> +	return true;
Jan> +
Jan> +      for (auto range : ranges ())
Jan> +	{
Jan> +	  if (range.start () <= addr && addr < range.end ())
Jan> +	    return true;

It took me a long time to understand that this patch was doing the real
work in this series...

For this method I guess there is an invariant that the block's start is
the minimum of the range minima and the block's end is the maximum of
the range maxima.

It seems to me that since this is an important feature, it ought to be
enforced by an assert, if necessary adding checks in the reader to
ensure that bad DWARF doesn't cause an assertion failure.

Jan> @@ -857,7 +876,10 @@ blockvector::lookup (CORE_ADDR addr) const
Jan>        if (b->start () > addr)
Jan>  	return nullptr;
Jan>        if (b->end () > addr)
Jan> -	return b;
Jan> +	{
Jan> +	  if (b->contains (addr))
Jan> +	    return b;
Jan> +	}
Jan>        bot--;
Jan>      }
 
The heart of the series.

I wonder about the efficiency of this.  Like how many blocks can we
expect to see in the linear phase?

I don't know what a representative program might be here.

Tom