On Mon, 29 Jun 2026, Filip Kastl wrote:
> > On Mon, 29 Jun 2026, Filip Kastl wrote:
> > > Ah and one more detail: I'm working with all constraints involving uses
> > > and
> > > clobbers disabled (I don't call
> > > gimple-ssa-pta-constraints.cc:find_func_clobbers). I'm mentioning that
> > > in case
> > > you'd be confused that some constraints are missing.
> > >
> > > But the mystery of why Andersen decides to fill those sets remains.
> > >
> > > Filip
> > >
> > > On Mon 2026-06-29 11:57:49, Filip Kastl wrote:
> > > > Hi Richi,
> > > >
> > > > I have another question about PTA that may or may not be related to the
> > > > last
> > > > week's question.
> > > >
> > > > I'm debugging a difference between what my Steensgaard-style solver and
> > > > what
> > > > GCC's Andersen-style solver compute. In particular on my testcase
> > > > (gcc_r from
> > > > 2017 SPEC CPU) Steensgaard computes these sets...
> > > >
> > > > ix86_encode_section_info.clobber = { }
> > > > ix86_encode_section_info.use = { }
> > > > ix86_encode_section_info.result = { }
> > > > ix86_encode_section_info.arg0 = { NULL ANYTHING STRING ESCAPED N ...
> > > > ix86_encode_section_info.arg1 = { NULL ANYTHING STRING ESCAPED N ...
> > > > ix86_encode_section_info.arg2 = { }
> > > >
> > > > ...while Steensgaard computes this:
> > > >
> > > > ix86_encode_section_info.clobber = { NULL ANYTHING p p }
> > > > ix86_encode_section_info.use = { NULL ANYTHING p p }
> > > > ix86_encode_section_info.result = { NULL ANYTHING p p }
> > > > ix86_encode_section_info.arg0 = { NULL ANYTHING p p }
> > > > ix86_encode_section_info.arg1 = { NULL ANYTHING p p }
> > > > ix86_encode_section_info.arg2 = { NULL ANYTHING p p }
> > > >
> > > > To figure out how Andersen arrived at these sets I searched the IPA PTA
> > > > dump
> > > > for constraints involving ix86_encode_section_info*. I found only
> > > > these...
> >
> > It's been some time since I had the Andersen code swapped in my brain,
> > so please bear with me eventually giving false hints ...
> >
> > > > Generating constraints for ix86_encode_section_info/332
> > > > (ix86_encode_section_info)
> > > > _18 = *ix86_encode_section_info.arg1
> > > > _19 = *ix86_encode_section_info.arg1 + 64
> > > > _24 = *ix86_encode_section_info.arg0
> > > > *_26 + 5 = ix86_encode_section_info.arg0
> > > > _30 = *ix86_encode_section_info.arg0
> > > > _31 = *ix86_encode_section_info.arg0 + 1165
> > > > _32 = *ix86_encode_section_info.arg0 + 1160
> > > > *_38 + 5 = ix86_encode_section_info.arg0
> > > > _41 = *ix86_encode_section_info.arg0
> > > > _44 = *ix86_encode_section_info.arg0 + 472
> > > > _46 = *ix86_encode_section_info.arg0 + 24
> > > > _1 = *ix86_encode_section_info.arg0
> > > > _2 = *ix86_encode_section_info.arg0 + 24
> > > > _4 = *ix86_encode_section_info.arg0 + 472
> > > > _55 = *ix86_encode_section_info.arg0
> > > > _56 = *ix86_encode_section_info.arg0 + 1024
> > > > _60 = *ix86_encode_section_info.arg0 + 128
> > > > _17 = *ix86_encode_section_info.arg1 + 64
> > > >
> > > > ...which is strange. I don't see any assigning into
> > > > ix86_encode_section_info*
> > > > nor assigning &ix86_encode_section_info* into any other set. Shouldn't
> > > > then
> > > > Andersen compute empty sets for all of these? (Although it is a good
> > > > thing
> > > > that Andersen fills those sets. Otherwise, there would be a
> > > > miscompilation.
> > > > I just want to understand what is it that my solver fails to do here.)
> >
> > There must be call sites of ix86_encode_section_info/332 and I'd expect
> > those to have constraints like
> >
> > ix86_encode_section_info.arg0 = ...
>
> I don't see any constraints like this. But since the function only gets
> called
> indirectly, that makes sense to me.
>
> > &ix86_encode_section_info itself would appear when the function is only
> > called indirectly ...
> >
> > > > First explanation I came up with was expanding of
> > > > ix86_encode_section_info (the
> > > > fninfo) using '+ UNKNOWN' that we discussed last week. But
> > > > ix86_encode_section_info is not present in any constraint at all so it
> > > > cannot
> > > > be present in any pt set and therefore it cannot get expanded this way.
> > > >
> > > > Note that ix86_encode_section_info is only ever called indirectly
> > > > through a
> > > > function pointer targetm.encode_section_info. That may be relevant
> > > > here, I
> > > > think.
> >
> > ... as you say here. It might be only visible when creating
> > constraints for the targem initializer (a global).
>
> Not sure what you mean by this sentence ^. Could you expand on this a bit?
>
> > We might end up
> > with just feeding that from NONLOCAL and thus you'd get ESCAPED
> > at uses and ix86_encode_section_info should be escaped?
>
> Hm, doesn't look like ix86_encode_section_info escaped though:
>
> ESCAPED = { NULL ANYTHING STRING ESCAPED NONLOCAL output_object_block_htab
> const_desc_eq assemble_real.arg0 mark_constant object_block_entry_hash
> gt_pch_p_P23constant_descriptor_rtx4htab gt_pch_p_17rtx_constant_pool
> const_rtx_hash_1 section_entry_eq emutls_common_1 const_desc_rtx_eq
> section_entry_hash gt_pch_p_23constant_descriptor_rtx compute_reloc_for_rtx_1
> const_desc_rtx_hash const_desc_hash object_block_entry_eq
> build_int_cst_wide_type.arg1 build_int_cst_wide_type.arg2 type_hash_eq
> gt_pch_p_P9type_hash4htab gt_pch_p_9type_hash cl_option_hash_eq
> cl_option_hash_hash type_hash_hash tree_map_hash tree_map_base_hash
> tree_map_base_eq int_cst_hash_eq int_cst_hash_hash
> gt_pch_p_17stack_local_entry ix86_init_machine_status
> extended_reg_mentioned_1 get_some_local_dynamic_name_1 dconst0 dconsthalf
> dconstm1 internal_label_prefix optab_table dconst1 isa_other target_other
> name name label tmp_label key.0+64 key.0+64 buf buf buffer x reloc flagchars
> ggc_calloc ggc_free in.0+64 label tmp.0+64
x h label data body in.0+64 lhd_dwarf_name gimple_decl_printable_name
lhd_set_decl_assembler_name gimple_fold_obj_type_ref mode_name_buf D.16879.0+64
D.16880.0+64 dc p code code precision in.0+64 in.0+64 in.0+64 in.0+64 in.0+64
in.0+64 in in p low1 hi d.0+32 TWO52r.0+32 half_minus_pred_half.0+32
pred_half.0+32 TWO52r.0+32 TWO52r.0+32 TWO52r.0+32 TWO52r.0+32 TWO52r.0+32
TWO52r.0+32 half_minus_pred_half.0+32 pred_half.0+32 r.0+32 inf.0+32 words use
r.0+32 dstr dstr ONE16r.0+32 TWO31r.0+32 r.0+32 l xops xops name r.0+32
cur_target rperm rperm rperm rperm name xops rperm buf name } same as
lookup_constant_def.result
Oh, and it's there! Once ANYTHING is in a set it won't expand
further.
>
> In fact, I don't see ix86_encode_section_info in any PT set in the dump.
>
> > > >
> > > > Do you have any hunch about what is going on here? How does the
> > > > Andersen
> > > > solver decide to fill those sets?
> >
> > the indirect call.
> >
> > Richard.
>
> In the meantime I've managed to get GDB into the place where the
> ix86_encode_section_info.arg1 gets filled. I'll try to step through the
> Andersen solver and see if I can figure out what's going on that way. Here's
> the stack trace in case you're interested:
>
> #0 bitmap_list_insert_element_after (head=<optimized out>,
> elt=elt@entry=0x0, indx=<optimized out>,
> node=0x5b64bb0, node@entry=0x0) at ../../thesis-src/gcc/bitmap.cc:328
> #1 0x0000000000aa77d6 in bitmap_elt_copy (dst=<optimized out>,
> dst_elt=<optimized out>, dst_prev=0x0,
> src_elt=0x5bbefb8, changed=true) at ../../thesis-src/gcc/bitmap.cc:1506
> #2 bitmap_elt_ior (dst=<optimized out>, dst_elt=<optimized out>,
> dst_prev=0x0, a_elt=<optimized out>,
> b_elt=<optimized out>, changed=<optimized out>) at
> ../../thesis-src/gcc/bitmap.cc:2055
> #3 0x0000000000aaac19 in bitmap_ior_into (a=0x3c4be50, b=b@entry=0x3f2c410)
> at ../../thesis-src/gcc/bitmap.cc:2131
> #4 0x00000000013df790 in solve_graph (graph=0x3b38ef0) at
> ../../thesis-src/gcc/pta-andersen.cc:2385
>
> 2377 {
> 2378 to_remove = j;
> 2379 if (bitmap_set_bit (get_varinfo (to)->solution,
> 2380 escaped_id))
> 2381 bitmap_set_bit (changed, to);
> 2382 continue;
> 2383 }
> 2384
> 2385 if (bitmap_ior_into (get_varinfo (to)->solution,
> pts)) <----------------
> 2386 bitmap_set_bit (changed, to);
> 2387 }
> 2388 if (to_remove != ~0U)
> 2389 bitmap_clear_bit (graph->succs[i], to_remove);
> 2390 }
> 2391 }
>
> Thanks,
> Filip
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
