[Bug default/25566] New: [dwz] Take reference size into account in heuristics

[Bug default/25566] New: [dwz] Take reference size into account in heuristics

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=25566

            Bug ID: 25566
           Summary: [dwz] Take reference size into account in heuristics
           Product: dwz
           Version: unspecified
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: default
          Assignee: nobody at sourceware dot org
          Reporter: vries at gcc dot gnu.org
                CC: dwz at sourceware dot org
  Target Milestone: ---

When looking at executables produced by a lazy DWARF producer, we find that all
the intra-CU references are done using DW_FORM_ref4:
...
$ readelf -wa cc1 \
  | grep DW_FORM_ref \
  | egrep -v "DW_FORM_ref4|DW_FORM_ref_addr" \
  | wc -l
0
...

In such a case, if we move a DIE out of a CU into a PU, we replace a
DW_FORM_ref4 (size 4 bytes) with a DW_FORM_ref_addr (size 4 bytes in 32-bit
DWARF), so, it's size neutral.

However, if we handle an executable containing minimal intra-CU references, the
substitution is no longer size-neutral. We should take that into account in the
heuristics.

In order to do that, we should track for lower top-level DIEs the number of
intra-cu references, and their combined size.

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