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Re: LTO : question about get_untransformed_body
On Wed, Dec 4, 2019 at 6:03 PM Erick Ochoa
<erick.ochoa@theobroma-systems.com> wrote:
>
>
>
> On 2019-12-04 7:52 a.m., Richard Biener wrote:
> > On Tue, Dec 3, 2019 at 11:51 PM Erick Ochoa
> > <erick.ochoa@theobroma-systems.com> wrote:
> >>
> >> Hi,
> >>
> >> I am trying to use the function: `cgraph_node::get_untransformed_body` during
> >> the wpa stage of a SIMPLE_IPA_PASS transformation. While the execute function
> >
> > I think SIMPLE_IPA_PASSes have no "WPA" stage but run at LTRANS time
> > (WPA transform stage). So you might simply see that not all bodies are
> > available in your LTRANS unit?
> >
>
> This makes a lot of sense, and it is indeed documented in the GCC internals
> manual:
>
> A small inter-procedural pass (SIMPLE_IPA_PASS) is a pass that does
> everything at once and thus it can not be executed during WPA in WHOPR
> mode. It defines only the Execute stage and during this stage it
> accesses and modifies the function bodies. Such passes are useful for
> optimization at LGEN or LTRANS time and are used, for example, to
> implement early optimization before writing object files.
>
> I got confused because the dump_file for my pass includes the substring 'wpa'.
> Should I file a bug to change the name of the dumpfile to something more like
> `ltrans*`?
Well, you probably placed your pass in the IPA pipeline rather than the
all_late_ipa_passes one? In principle IPA passes _can_ pull in bodies
during WPA
analysis, that just will be very costly.
> Thanks for your help!
>
> >> is running, I need to access the body of a function in order to iterate over
> >> the gimple instructions in the first basic block. I have found that the
> >> majority of the cgraph_node will return successfully. However, there are some
> >> functions which consistently produce a segmentation fault following this
> >> stacktrace:
> >>
> >> ```
> >> 0xbc2adb crash_signal
> >> /home/eochoa/code/gcc/gcc/toplev.c:328
> >> 0xa54858 lto_get_decl_name_mapping(lto_file_decl_data*, char const*)
> >> /home/eochoa/code/gcc/gcc/lto-section-in.c:367
> >> 0x7030e7 cgraph_node::get_untransformed_body()
> >> /home/eochoa/code/gcc/gcc/cgraph.c:3516
> >> 0x150613f get_bb1_callees
> >> /home/eochoa/code/gcc/gcc/ipa-initcall-cp.c:737
> >> 0x150613f reach_nodes_via_bb1_dfs
> >> ```
> >>
> >> Is there a way for `cgraph_node::get_untransformed_body` to succeed
> >> consistently? (I.e. are there some preconditions that I need to make sure are
> >> in place before calling cgraph_node::get_untransformed_body?
> >>
> >> I am using gcc version 10.0.0 20191127 (experimental)
> >>
> >> Thanks