On Thu, 14 Mar 2024, Jan Hubicka wrote:
> > > We have wrong code with LTO, too.
> >
> > I know.
> >
> > > The problem is that IPA passes (and
> > > not only that, loop analysis too) does analysis at compile time (with
> > > value numbers in) and streams the info separately.
> >
> > And that is desirable, because otherwise it simply couldn't derive any
> > ranges.
> >
> > > Removal of value ranges
> > > (either by LTO or by your patch) happens between computing these
> > > summaries and using them, so this can be used to trigger wrong code,
> > > sadly.
> >
> > Yes. But with LTO, I don't see how the IPA ICF comparison whether
> > two functions are the same or not could be done with the
> > SSA_NAME_{RANGE,PTR}_INFO in, otherwise it could only ICF merge functions
> > from the same TUs. So the comparison IMHO (and the assert checks in my
> > patch prove that) is done when the SSA_NAME_{RANGE,PTR}_INFO aren't in
> > anymore. So, one just needs to compare and punt or union whatever
> > is or could be influenced in the IPA streamed data from the ranges etc.
> > And because one has to do it for LTO, doing it for non-LTO should be
> > sufficient too.
>
> Sorry, this was bit of a misunderstanding: I tought you still considered
> the original patch to be full fix, while I tought I should look into it
> more and dig out more issues. This is bit of can of worms. Overall I
> think the plan is:
>
> This stage4
> 1) fix VR divergences by either comparing or droping them
> 2) fix jump function differences by comparing them
> (I just constructed a testcase showing that jump functions can
> diverge for other reasons than just VR, so this is deeper problem,
> too)
> 3) try to construct aditional wrong code testcases (finite_p
> divergences, trapping)
> Next stage1
> 4) implement VR and PTR info streaming
> 5) make ICF to compare VRs and punt otherwise
> 6) implement optimize_size feature to ICF that will not punt on
> diverging TBAA or value ranges and do merging instead.
> We need some extra infrastructure for that, being able to keep the
> maps between basic blocks and SSA names from comparsion stage to
> merging stage
> 7) measure how effective ICF becomes in optimize_size mode and implement
> heuristics on how much metadata merging we want to do with -O2/-O3 as
> well.
> Based on older data Martin collected for his thesis, ICF used to be
> must more effective on libreoffice then it is today, so hopefully we
> can recover 10-15% binary size improvmeents here.
> 8) General ICF TLC. There are many half finished things for a while in
> this pass (such as merging with different BB or stmt orders).
>
> I am attaching the compare patch which also fixes the original wrong
> code. If you preffer your version, just go ahead to commit it. Otherwise
> I will add your testcase for this patch and commit this one.
> Statistically we almost never merge functions with different value
> ranges (three in testsuite, 0 during bootstrap, 1 during LTO bootstrap
> and probably few in LLVM build - there are 15 cases reported, but some
> are false positives caused by hash function conflicts).
>
> Honza
>
> gcc/ChangeLog:
>
> * ipa-icf-gimple.cc (func_checker::compare_ssa_name): Compare value
> ranges.
>
> diff --git a/gcc/ipa-icf-gimple.cc b/gcc/ipa-icf-gimple.cc
> index 8c2df7a354e..37c416d777d 100644
> --- a/gcc/ipa-icf-gimple.cc
> +++ b/gcc/ipa-icf-gimple.cc
> @@ -39,9 +39,11 @@ along with GCC; see the file COPYING3. If not see
> #include "cfgloop.h"
> #include "attribs.h"
> #include "gimple-walk.h"
> +#include "value-query.h"
> +#include "value-range-storage.h"
>
> #include "tree-ssa-alias-compare.h"
> #include "ipa-icf-gimple.h"
>
> namespace ipa_icf_gimple {
>
> @@ -109,6 +116,35 @@ func_checker::compare_ssa_name (const_tree t1,
> const_tree t2)
> else if (m_target_ssa_names[i2] != (int) i1)
> return false;
>
> + if (POINTER_TYPE_P (TREE_TYPE (t1)))
> + {
> + if (SSA_NAME_PTR_INFO (t1))
> + {
> + if (!SSA_NAME_PTR_INFO (t2)
> + || SSA_NAME_PTR_INFO (t1)->align != SSA_NAME_PTR_INFO (t2)->align
> + || SSA_NAME_PTR_INFO (t1)->misalign != SSA_NAME_PTR_INFO
> (t2)->misalign)
You want to compare SSA_NAME_PTR_INFO ()->pt.zero as well I think since
we store pointer non-null-ness from VRP there.
You are not comparing the actual points-to info - but of course I'd
expect that to differ as soon as local decls are involved. Still looks
like a hole to me.
> + return false;
> + }
> + else if (SSA_NAME_PTR_INFO (t2))
> + return false;
> + }
> + else
> + {
> + if (SSA_NAME_RANGE_INFO (t1))
> + {
> + if (!SSA_NAME_RANGE_INFO (t2))
> + return false;
> + Value_Range r1 (TREE_TYPE (t1));
> + Value_Range r2 (TREE_TYPE (t2));
> + SSA_NAME_RANGE_INFO (t1)->get_vrange (r1, TREE_TYPE (t1));
> + SSA_NAME_RANGE_INFO (t2)->get_vrange (r2, TREE_TYPE (t2));
> + if (r1 != r2)
> + return false;
> + }
> + else if (SSA_NAME_RANGE_INFO (t2))
> + return false;
> + }
> +
> if (SSA_NAME_IS_DEFAULT_DEF (t1))
> {
> tree b1 = SSA_NAME_VAR (t1);
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
