> Hi,
>
> I'm re-posting patches which I have posted at the end of stage 1 but
> which have not passed review yet.
>
> 8<--------------------------------------------------------------------
>
> C++ and especially Fortran pass data by references which are not
> pointers potentially pointing anywhere and so can be assumed to be
> safely dereferencable. This patch teaches IPA-SRA to treat them as
> such and avoid the dance we do to prove that we can move loads from
> them to the caller.
>
> When we do not know that a dereference will happen all the time, we
> need a heuristics so that we do not force memory accesses that normally
> happen only rarely. The patch simply uses the (possibly guessed)
> profile and checks whether the (expected) number of loads is at least
> half of function invocations invocations.
>
> Bootstrapped and tested individually when I originally posted it and
> now bootstrapped and LTO-bootstrapped and tested as part of the whole
> series. OK for master?
>
>
> gcc/ChangeLog:
>
> 2022-11-11 Martin Jambor <mjam...@suse.cz>
>
> PR ipa/103585
> * ipa-sra.c (struct gensum_param_access): New field load_count.
> (struct gensum_param_desc): New field safe_ref, adjusted comments.
> (by_ref_count): Renamed to unsafe_by_ref_count, adjusted all uses.
> (dump_gensum_access): Dump the new field.
> (dump_gensum_param_descriptor): Likewise.
> (create_parameter_descriptors): Set safe_ref field, move setting
> by_ref forward. Only increment unsafe_by_ref_count for unsafe
> by_ref parameters.
> (allocate_access): Initialize new field.
> (mark_param_dereference): Adjust indentation. Only add data to
> bb_dereferences for unsafe by_ref parameters.
> (scan_expr_access): For loads, accumulate BB counts.
> (dereference_probable_p): New function.
> (check_gensum_access): Fix leading comment, add parameter FUN.
> Check cumulative counts of loads for safe by_ref accesses instead
> of dereferences.
> (process_scan_results): Do not propagate dereference distances for
> safe by_ref parameters. Pass fun to check_gensum_access. Safe
> by_ref params do not need the postdominance check.
>
> gcc/testsuite/ChangeLog:
>
> 2022-11-11 Martin Jambor <mjam...@suse.cz>
>
> * g++.dg/ipa/ipa-sra-5.C: New test
> -/* Perform basic checks on ACCESS to PARM described by DESC and all its
> - children, return true if the parameter cannot be split, otherwise return
> - true and update *TOTAL_SIZE and *ONLY_CALLS. ENTRY_BB_INDEX must be the
> - index of the entry BB in the function of PARM. */
> +/* Return true if the ACCESS loads happen frequently enough in FUN to risk
> + moving them to the caller and only pass the result. */
>
> static bool
> -check_gensum_access (tree parm, gensum_param_desc *desc,
> +dereference_probable_p (struct function *fun, gensum_param_access *access)
> +{
> + return access->load_count
> + >= ENTRY_BLOCK_PTR_FOR_FN (fun)->count.apply_scale (1, 2);
We may want to have --param for this.
Otherwise the patch is OK.
Honza
