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Re: LTO bootstrap compare errors for ARM64


> On Wed, Aug 20, 2014 at 9:28 AM, Venkataramanan Kumar
> <venkataramanan.kumar@linaro.org> wrote:
> > Hi Honza,
> >
> > After discussing with Richard Beiner via
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62077, it look like it is
> > an existing problem in trunk and is masked due the fact that stage1
> > and stage2 compilers in trunk are built with enable-checking and hence
> > same garbage collection tuning parameters.
> 
> Note that it works on trunk with --enable-checking=release for
> whatever reason.

Strange, do you know how the IR is affected by garbage collection?

Honza
> 
> > In release branches, stage 1 is built with some checks like "gc" but
> > stage 2 is not.
> > These gc parameters affect the LTO IR and it gets streamed differently.
> >
> > Currently for release branches we have workaround of setting same gc
> > parameters for stage1 and stage2 builds (or) build stage1 with
> > ---enable-checking=release.
> >
> > regards,
> > Venkat
> >
> >
> > On 11 August 2014 16:20, Venkataramanan Kumar
> > <venkataramanan.kumar@linaro.org> wrote:
> >> Hi Honza,
> >>
> >> I did not find any differences in tree level dumps. These are the dump
> >> differences in IPA
> >>
> >> In gimple-fold.c.000i.cgraph
> >>
> >> (--Snip--)
> >> < _Z25gimple_build_omp_continueP9tree_nodeS0_/761
> >> (gimple_build_omp_continue(tree_node*, tree_node*)) @0x3ff7ebda548
> >> ---
> >>> _Z25gimple_build_omp_continueP9tree_nodeS0_/761 (gimple_build_omp_continue(tree_node*, tree_node*)) @0x3ff92b5a548
> >> 28865c28865
> >> < _Z26gimple_build_omp_taskgroupP21gimple_statement_base/760
> >> (gimple_build_omp_taskgroup(gimple_statement_base*)) @0x3ff7ebda400
> >> ---
> >>> _Z26gimple_build_omp_taskgroupP21gimple_statement_base/760 (gimple_build_omp_taskgroup(gimple_statement_base*)) @0x3ff92b5a400
> >> 28875c28875
> >> < _Z23gimple_build_omp_masterP21gimple_statement_base/759
> >> (gimple_build_omp_master(gimple_statement_base*)) @0x3ff7ebda2b8
> >> ---
> >>> _Z23gimple_build_omp_masterP21gimple_statement_base/759 (gimple_build_omp_master(gimple_statement_base*)) @0x3ff92b5a2b8
> >> 28885c28885
> >> < _Z24gimple_build_omp_sectionP21gimple_statement_base/758
> >> (gimple_build_omp_section(gimple_statement_base*)) @0x3ff7ebda170
> >> ---
> >>> _Z24gimple_build_omp_sectionP21gimple_statement_base/758 (gimple_build_omp_section(gimple_statement_base*)) @0x3ff92b5a170
> >> (--Snip--)
> >>
> >>
> >> In gimple.c.044i.profile_estimate
> >>
> >> (--Snip--)
> >>
> >> 1987c1987
> >> < vec<tree_node*, va_heap, vl_ptr>::qsort(int (*)(void const*, void
> >> const*)) (struct vec * const this, int (*<T10f9>) (const void *, const
> >> void *) cmp)
> >> ---
> >>> vec<tree_node*, va_heap, vl_ptr>::qsort(int (*)(void const*, void const*)) (struct vec * const this, int (*<T10fb>) (const void *, const void *) cmp)
> >> (--Snip--)
> >>
> >> gimple.c.048i.inline
> >>
> >> (--Snip--)
> >>
> >> <   min size:       6
> >> ---
> >>>   min size:       0
> >> 6590c6590
> >> <   min size:       14
> >> ---
> >>>   min size:       0
> >> 6607c6607
> >> <   min size:       28
> >> (--Snip--)
> >>
> >> On 7 August 2014 19:14, Jan Hubicka <hubicka@ucw.cz> wrote:
> >>>>
> >>>> As a First step I compared the "objump -D" dump between
> >>>> "stage2-gcc/gimple.o"  and "stage3-gcc/gimple.o".  Differences are in
> >>>> LTO sections .gnu.lto_.decls.0, .gnu.lto_.symtab.
> >>>> Ref: http://paste.ubuntu.com/7949238/
> >>>
> >>> If you see the differences already in .o files (i.e. at compile time), I think the next
> >>> step is to produce -fdump-tree-all -fdump-ipa-all dumps of stage2-gcc/gimple.o
> >>> and stage3-gcc/gimple.o and see how they differ.
> >>>
> >>> Debugging misoptimization of LTO stage2 compiler will be interesting - I guess we can
> >>> first try to identify what is wrong rahter than usual bisecting method...
> >>>
> >>> Honza
> >>>>
> >>>> No differences when when using "objdump -d".
> >>>>
> >>>> Next I passed "-save-temps" to stage2 and stage3 builds and compared
> >>>> the assembly files. The differences are in strings dumped via .ascii
> >>>> and ,string directives.
> >>>>
> >>>> Next I checked the flags passed to the stage 2 and stage 3 builds. It
> >>>> is same and below is the flag set being passed.
> >>>>
> >>>> -save-temps -O2 -g -flto -flto=jobserver -frandom-seed=1
> >>>> -ffat-lto-objects -DIN_GCC    -fno-exceptions -fno-rtti
> >>>> -fasynchronous-unwind-tables -W -Wall -Wno-narrowing -Wwrite-strings
> >>>> -Wcast-qual -Wmissing-forma        t-attribute -pedantic
> >>>> -Wno-long-long -Wno-variadic-macros -Wno-overlength-strings
> >>>>
> >>>>  Can you please suggest on how to fix/debug further these comparison
> >>>> failures in GCC 4.9?
> >>>>
> >>>> regards,
> >>>> Venkat.


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