https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92801
Bug ID: 92801
Summary: Drop unused struct fields
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ipa
Assignee: unassigned at gcc dot gnu.org
Reporter: christoph.muell...@theobroma-systems.com
CC: marxin at gcc dot gnu.org
Target Milestone: ---
Non-escaping structs [1] can have their unused fields removed such that
they have a smaller memory footprint and thus allow
a more efficient cache utilisation.
We are currently working on such a pass and want to use this
ticket to further publish details and patches, and to collect
feedback from the community.
First implementation details:
* Iterate with gsi over function bodies to find field accesses
(e.g. in assignment, call, cond or switch statements).
* Allowed for removal if never accessed
* Allowed for removal if write-only (incl. removal of write statements)
* Removal based on modification of DECL_CHAIN() of TYPE_FIELDS(t)
Early tests showed, that this has the potential to eliminate
struct fields nextout and nextin from struct arc of CPU2017's mcf benchmark.
As elements of an struct arc array are accessed for the main calculation in
the hot loop, this benchmark is a good example, where this pass will help.
[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92800
