Re: [PATCH 6/9] ipa-sra: Be optimistic about Fortran descriptors

[Jan Hubicka <hubicka@ucw.cz>]

> Hi,
> 
> I'm re-posting patches which I have posted at the end of stage 1 but
> which have not passed review yet.
> 
> 8<--------------------------------------------------------------------
> 
> Fortran descriptors are structures which are often constructed just
> for a particular argument of a particular call where it is passed by
> reference.  When the called function is under compiler's control, it
> can be beneficial to split up the descriptor and pass it in individual
> parameters.  Unfortunately, currently we allow IPA-SRA to replace a
> pointer with a set of replacements which are at most twice as big in
> total and for descriptors we'd need to bump that factor to seven.
> 
> This patch looks for parameters which are ADDR_EXPRs of local
> variables which are written to and passed as arguments by reference
> but are never loaded from and marks them with a flag in the call edge
> summary.  The IPA analysis phase then identifies formal parameters
> which are always fed such arguments and then is more lenient when it
> comoes to size.
> 
> In order not to store to maximums per formal parameter, I calculate
> the more lenient one by multiplying the existing one with a new
> parameter.  If it is preferable to keep the maximums independent, we
> can do that.  Documentation for the new parameter is missing as I
> still need to re-base the patch on a version which has sphinx.  I will
> write it before committing.
> 
> I have disable IPA-SRA in pr48636-2.f90 in order to be able to keep
> using its dump-scan expressions.  The new testcase is basically a copy
> of it with different options and IPA-SRA dump scans.
> 
> 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  <mjambor@suse.cz>
> 
> 	* ipa-sra.c (isra_param_desc): New field not_specially_constructed.
> 	(struct isra_param_flow): New field constructed_for_calls.
> 	(isra_call_summary::dump): Dump the new flag.
> 	(loaded_decls): New variable.
> 	(dump_isra_param_descriptor): New parameter hints, dump
> 	not_specially_constructed if it is true.
> 	(dump_isra_param_descriptors): New parameter hints, pass it to
> 	dump_isra_param_descriptor.
> 	(ipa_sra_function_summaries::duplicate): Duplicate new flag.
> 	(create_parameter_descriptors): Adjust comment.
> 	(get_gensum_param_desc): Bail out when decl2desc is NULL.
> 	(scan_expr_access): Add loaded local variables to loaded_decls.
> 	(scan_function): Survive if final_bbs is NULL.
> 	(isra_analyze_call): Compute constructed_for_calls flag.
> 	(process_scan_results): Be optimistic about size limits.  Do not dump
> 	computed param hints when dumpint IPA-SRA structures.
> 	(isra_write_edge_summary): Stream constructed_for_calls.
> 	(isra_read_edge_summary): Likewise.
> 	(ipa_sra_dump_all_summaries): New parameter hints, pass it to
> 	dump_isra_param_descriptor.
> 	(flip_all_hints_pessimistic): New function.
> 	(flip_all_param_hints_pessimistic): Likewise.
> 	(propagate_param_hints): Likewise.
> 	(disable_unavailable_parameters): Renamed to
> 	adjust_parameter_descriptions.  Expand size limits for parameters
> 	which are specially contstructed by all callers.  Check limits again.p
> 	(ipa_sra_analysis): Pass required hints to ipa_sra_dump_all_summaries.
> 	Add hint propagation.
> 	(ipa_sra_summarize_function): Initialize and destory loaded_decls,
> 	rearrange so that scan_function is called even when there are no
> 	candidates.
> 	* params.opt (ipa-sra-ptrwrap-growth-factor): New parameter.

Hmm, this is quite specific heuristics, but I do not have much better
ideas, so it is OK :)

Can this be useful also for inlining?

Honza