[llvm-dev] [RFC] - Deduplication of debug information in linkers (LLD)
Rui Ueyama via llvm-dev
llvm-dev at lists.llvm.org
Mon Dec 4 20:58:37 PST 2017
Jon,
I think what George suggested is different from making lld to parse,
deduplicate and rewrite the DWARF debug info. What he suggested is to make
the compiler emit multiple debug sections so that the linker can eliminate
them just like it does for, for example, inline functions. The elimination
is done by (essentially) section name, so it should be quite fast. Parsing
all debug info and reconstructing it is completely different IMO.
On Mon, Dec 4, 2017 at 3:58 PM, Jon Chesterfield via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> At least one proprietary linker put a lot of effort into deduplicating and
> rewriting debug information. This took up the majority of the link time
> despite serious engineering time on performance optimisation. For example,
> some sections were written from scratch by the linker because that proved
> faster than parsing the input. Teaching LLD to dedup DWARF should be
> expected to dramatically slow it down (when enabled, ideally not when
> disabled).
>
> Is a more incremental approach viable? In particular, are there IR passes
> that fold debug strings etc that could be deployed before feeding
> everything into a linker?
>
>
> On Mon, Dec 4, 2017 at 10:59 PM, via llvm-dev <llvm-dev at lists.llvm.org>
> wrote:
>
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>> Today's Topics:
>>
>> 1. Re: [RFC] Half-Precision Support in the Arm Backends
>> (Friedman, Eli via llvm-dev)
>> 2. LLVM Weekly - #205, Dec 4th 2017 (Alex Bradbury via llvm-dev)
>> 3. Re: [RFC] - Deduplication of debug information in linkers
>> (LLD). (UE US via llvm-dev)
>> 4. Re: [RFC] - Deduplication of debug information in linkers
>> (LLD). (UE US via llvm-dev)
>> 5. Adding a string-argument Intrinsic (Dounia Khaldi via llvm-dev)
>> 6. Re: Adding a string-argument Intrinsic
>> (Jonathan Roelofs via llvm-dev)
>> 7. Passes to add/validate synthetic debug info
>> (Vedant Kumar via llvm-dev)
>> 8. Re: Passes to add/validate synthetic debug info
>> (Davide Italiano via llvm-dev)
>> 9. Re: [RFC] - Deduplication of debug information in linkers
>> (LLD). (Eric Christopher via llvm-dev)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Mon, 4 Dec 2017 12:20:11 -0800
>> From: "Friedman, Eli via llvm-dev" <llvm-dev at lists.llvm.org>
>> To: Sjoerd Meijer <Sjoerd.Meijer at arm.com>, "llvm-dev at lists.llvm.org"
>> <llvm-dev at lists.llvm.org>
>> Subject: Re: [llvm-dev] [RFC] Half-Precision Support in the Arm
>> Backends
>> Message-ID: <71e3a663-1b80-8c77-c495-9b5a30ade76a at codeaurora.org>
>> Content-Type: text/plain; charset="windows-1252"; Format="flowed"
>>
>> On 12/4/2017 6:44 AM, Sjoerd Meijer via llvm-dev wrote:
>> >
>> > Custom Lowering
>> > -------------------------
>> >
>> > Making f16 legal and not having native load/stores instructions
>> available,
>> > (no FullFP16 support) means custom lowering loads/stores:
>> > 1) Since we don't have FP16 load/store instructions available, we create
>> > integer half-word loads. I unfortunately need the FP16_TO_FP node
>> here,
>> > because that "models" creating an integer value, which is what we
>> need
>> > to create a "truncating i16" integer load instructions. Instead, of
>> > using
>> > FP16_TO_FP, I have tried BITCASTs, but this can lead to code
>> generation
>> > to stack loads/stores which I don't want.
>> > 2) Custom lowering f16 stores is very similar, and creates truncating
>> > half-word integer stores.
>>
>> Technically, there are no f16 load/store instructions, yes, but we can
>> use NEON vdl1 and vst1 to get something roughly equivalent, right?
>>
>> You probably want to custom-lower BITCAST instructions; the generic
>> sequence emitted by the legalizer is pretty inefficient in most cases.
>>
>> ---
>>
>> Overall, I think your approach makes sense.
>>
>> -Eli
>>
>> --
>> Employee of Qualcomm Innovation Center, Inc.
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
>> Linux Foundation Collaborative Project
>>
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>> ------------------------------
>>
>> Message: 2
>> Date: Mon, 4 Dec 2017 21:14:19 +0000
>> From: Alex Bradbury via llvm-dev <llvm-dev at lists.llvm.org>
>> To: llvm-dev <llvm-dev at lists.llvm.org>
>> Subject: [llvm-dev] LLVM Weekly - #205, Dec 4th 2017
>> Message-ID:
>> <CA+wH295CPJHG_trD4wbiqStUiN+AvhpwvMdNjcCtZuCWkONY_A at mail.gm
>> ail.com>
>> Content-Type: text/plain; charset="UTF-8"
>>
>> LLVM Weekly - #205, Dec 4th 2017
>> ================================
>>
>> If you prefer, you can read a HTML version of this email at
>> <http://llvmweekly.org/issue/205>.
>>
>> Welcome to the two hundred and fifth issue of LLVM Weekly, a weekly
>> newsletter
>> (published every Monday) covering developments in LLVM, Clang, and related
>> projects. LLVM Weekly is brought to you by [Alex
>> Bradbury](https://www.linkedin.com/in/alex-bradbury/). Subscribe to
>> future
>> issues at <http://llvmweekly.org> and pass it on to anyone else you
>> think may
>> be interested. Please send any tips or feedback to <asb at asbradbury.org>,
>> or
>> @llvmweekly or @asbradbury on Twitter.
>>
>> If you weren't able to make it to the 7th RISC-V Workshop in Milpitas last
>> week, you might find my
>> [blog](http://www.lowrisc.org/blog/2017/11/seventh-risc-v-wo
>> rkshop-day-one/)
>> [summary](http://www.lowrisc.org/blog/2017/11/seventh-risc-v
>> -workshop-day-two/)
>> on lowrisc.org useful.
>>
>>
>> ## News and articles from around the web
>>
>> LLVM/Clang 5.0.1-rc2 [has been
>> tagged](http://lists.llvm.org/pipermail/llvm-dev/2017-Novemb
>> er/119383.html).
>>
>> The call for papers has been
>> [issued](http://lists.llvm.org/pipermail/llvm-dev/2017-Novem
>> ber/119411.html)
>> for the LLVM Performance Workshop at CGO 2018. This will take place on
>> February 24th in Vienna, Austria.
>>
>>
>> ## On the mailing lists
>>
>> * Alexey Kukanov has published an RFC on [contributing Intel's Parallel
>> STL
>> implementation to
>> libc++](http://lists.llvm.org/pipermail/cfe-dev/2017-November/056135.html
>> ).
>>
>> * Artem Dergachev has [started to
>> document](http://lists.llvm.org/pipermail/cfe-dev/2017-Novem
>> ber/056095.html) a
>> number of issues preventing inlining in C++ code.
>>
>> * Mohammed Agabaria
>> [proposes](http://lists.llvm.org/pipermail/llvm-dev/2017-Nov
>> ember/119364.html)
>> adding a `no-overflow` keyword to the sdiv and udiv IR instructions.
>>
>> * Greg Clayton has responded to a user question with a [handy summary of
>> how
>> to remotely launch a new process in
>> LLDB](http://lists.llvm.org/pipermail/lldb-dev/2017-November/012979.html
>> ).
>>
>> * Jonas Thiem is [looking for
>> answers](http://lists.llvm.org/pipermail/llvm-dev/2017-Novem
>> ber/119269.html)
>> to a licensing question about the runtime libraries, and [further
>> elaborates](http://lists.llvm.org/pipermail/llvm-dev/2017-No
>> vember/119334.html)
>> in this follow-up.
>>
>>
>> ## LLVM commits
>>
>> * A new SpeculateAroundPHIs pass has been introduced. It's stunningly well
>> documented, so well worth a ready.
>> [r319164](http://reviews.llvm.org/rL319164).
>>
>> * The new `-stack-size-section` flag causes metadata to be emitted in an
>> ELF
>> section with information on function stack sizes.
>> [r319430](http://reviews.llvm.org/rL319430).
>>
>> * MergeConsecutiveStores is now run a second time, just before instruction
>> selection. This allows lowered intrinsics to be merged as well.
>> [r319036](http://reviews.llvm.org/rL319036).
>>
>> * The MachineVerifier PHI and register operand checking has been improved.
>> [r319140](http://reviews.llvm.org/rL319140),
>> [r319141](http://reviews.llvm.org/rL319141).
>>
>> * You can now use `-ppc-reg-with-percent-prefix` to get more readable PPC
>> assembler output. [r319381](http://reviews.llvm.org/rL319381).
>>
>> * The ARC backend can now assemble a subset of ARC instructions.
>> [r319609](http://reviews.llvm.org/rL319609).
>>
>>
>> ## Clang commits
>>
>> * clang-format gained options to control sorting of include blocks,
>> allowing
>> groups to be sorted individually, merged and sorted, and merged and
>> resplit.
>> [r319024](http://reviews.llvm.org/rL319024).
>>
>> * A number of math libcalls/builtins are now converted to equivalent LLVM
>> intrinsics. [r319593](http://reviews.llvm.org/rL319593).
>>
>> * clangd gained a fuzzy match scorer.
>> [r319557](http://reviews.llvm.org/rL319557).
>>
>>
>> ## Other project commits
>>
>> * LLD gained support for range extension thunks on AArch64.
>> [r319307](http://reviews.llvm.org/rL319307).
>>
>> * LLD has reduced the size of the .gnu.hash section.
>> [r319503](http://reviews.llvm.org/rL319503).
>>
>> * LLDB remote debugging documentation has been updated.
>> [r319213](http://reviews.llvm.org/rL319213).
>>
>>
>> ## Review corner
>>
>> The LLVM Weekly review corner serves to highlight patches that are stuck
>> waiting awaiting review, or work from first-time contributors. See
>> [here](http://llvmweekly.org/reviewcorner) for more information and how
>> to
>> submit you work for inclusion. Of course the hope is that highlighting
>> these
>> patches will enable LLVM Weekly readers will step up and help to get them
>> merged. I'll be reporting back each week on any activity generated on
>> these
>> patches, as well as sharing a new batch. If you want your patch included
>> you
>> must submit it via the linked form.
>>
>> After a quiet period, we've had some new patch submissions this week.
>> Three
>> were submitted, though [D38778](https://reviews.llvm.org/D38778)
>> (support for
>> the PowerPC Signal Processing Engine) has actually had reviews since being
>> submitted. Thanks Nemanja Ivanovic!
>>
>> * "Allows pretty printing of declarations through the libclang (C) API.
>> This
>> is useful for e.g. tooltips in an IDE - hover a function call and get the
>> corresponding declaration as tooltip."
>> [D39903](https://reviews.llvm.org/D39903), patch by Nikolai Kosjar.
>>
>> * "This patch extends clang's -verify option to support prefixes similar
>> to
>> FileCheck's --check-prefixes. While -verify plus preprocessor directives
>> could
>> already accomplish the same goal, source is often easier to read/maintain
>> without preprocessor directives or duplicate passages of code (see updated
>> clang tests in patch)." [D39694](https://reviews.llvm.org/D39694), patch
>> by
>> Joel E. Denny.
>>
>>
>> ------------------------------
>>
>> Message: 3
>> Date: Mon, 4 Dec 2017 15:20:53 -0600
>> From: UE US via llvm-dev <llvm-dev at lists.llvm.org>
>> To: George Rimar <grimar at accesssoftek.com>
>> Cc: "llvm-dev at lists.llvm.org" <llvm-dev at lists.llvm.org>
>> Subject: Re: [llvm-dev] [RFC] - Deduplication of debug information in
>> linkers (LLD).
>> Message-ID:
>> <CABQ7ENJjzD8i+YnZmK796-t9w06OhN45v5Jv_3mcy+Bo_MbxEw at mail.gm
>> ail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> Funny, I just filed a bug on that last night. Your solutions look like
>> they'll help me extensively as cutting the size if half will prevent my
>> 80GB make install issues.
>> https://bugs.llvm.org/show_bug.cgi?id=35512
>>
>> I'll leave the bug open for tracking purposes.
>>
>> GNOMETOYS
>>
>> On Mon, Dec 4, 2017 at 9:11 AM, George Rimar via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>> > Hi all !
>> >
>> > We have an issue with LLD, it is "relocation R_X86_64_32 out of range"
>> > (PR31109)
>> > which occurs during resolving relocations in debug sections. It looks
>> > happens
>> > because .debug_info section can be too large sometimes and 32x
>> relocation
>> > is not enough
>> > to represent the value. One of possible solutions looks to be to
>> > deduplicate information
>> > to reduce .debug_info size.
>> > The rest of mail contains information about experiments I did, the
>> > obtained results and
>> > some questions and suggestions as well.
>> >
>> > I was investigating idea to deduplicate debug types information. Idea is
>> > described at
>> > p276 of DWARF4 specification (http://www.dwarfstd.org/doc/DWARF4.pdf).
>> It
>> > suggests
>> > to split types information out of .debug_info and emit multiple
>> > .debug_types sections
>> > with use of COMDATs. Both clang and gcc I tested implements
>> > -fdebug-types-section flag for that:
>> >
>> > -fdebug-types-section, -fno-debug-types-section
>> > Place debug types in their own section (ELF Only)
>> > gcc's description is here: https://gcc.gnu.org/onlinedocs
>> /gcc-6.4.0/gcc/
>> > Debugging-Options.html#Debugging-Options.
>> >
>> > This flag is disabled by default. I compared clang binaries to see the
>> > difference
>> > with and without the linker side optimisation.
>> > 1) Clang built with -g has size of 1.7 GB, .debug_info section size is
>> > 894.5 Mb.
>> > 2) Clang built with -g -fdebug-types-section has size of 1.0 GB.
>> > .debug_types size is 26.267 MB, .debug_info size is 227.7 MB.
>> >
>> > Difference is huge and I believe shows (though probably for most of
>> > readers here it was
>> > already obvious) that optimization can be useful. Though
>> > -fdebug-types-section is disabled by default.
>> > Looks it was initially disabled because not all of DWARF consumers were
>> > aware of .debug_types section.
>> >
>> > Now in 2017 situation is different. I think most of DWARF consumers
>> knows
>> > about .debug_types, but:
>> > 1) DWARF5 specification explicitly eliminates the .debug_types section
>> > introduced in DWARF4:
>> > p8, "1.4 Changes from Version 4 to Version 5"
>> http://dwarfstd.org/doc/
>> > DWARF5.pdf
>> > 2) Instead of emiting multiple .debug_types it suggests to emit multiple
>> > .debug_info COMDAT
>> > sections. (p375, p376).
>> >
>> > And it seems currently there is no way to make clang to emit multiple
>> > .debug_info with type information
>> > like DWARF5 suggests. I tried command line below:
>> > -g -fdebug-types-section -gdwarf-5
>> > It still emits .debug_types and does not look there is a flag for
>> emiting
>> > multiple .debug_info.
>> > Looking at whole LLVM code (lib/mc, lib/CodeGen) actually it seems it is
>> > just always assumed .debug_info is
>> > a unique section in object.
>> > (also not sure why clang emits .debug_types when -gdwarf-5 flag is set,
>> as
>> > this section is incompatible with v5,
>> > probably it is a bug).
>> >
>> > So my questions are following:
>> > 1) Do we want to try to implement multiple .debug_info approach ? As it
>> > seems can be very useful sometimes.
>> > 2) For now in LLD may be we may want to extend our error message from
>> > "relocation X out of range" to something
>> > suggesting to use -fdebug-types-section (only for relocations in
>> debug
>> > sections) ?
>> > 3) Why -fdebug-types-section is disabled by default ?
>> >
>> >
>> > Best regards,
>> > George | Developer | Access Softek, Inc
>> >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >
>> >
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>>
>> ------------------------------
>>
>> Message: 4
>> Date: Mon, 4 Dec 2017 15:23:44 -0600
>> From: UE US via llvm-dev <llvm-dev at lists.llvm.org>
>> To: "Robinson, Paul" <paul.robinson at sony.com>
>> Cc: "llvm-dev at lists.llvm.org" <llvm-dev at lists.llvm.org>, George Rimar
>> <grimar at accesssoftek.com>
>> Subject: Re: [llvm-dev] [RFC] - Deduplication of debug information in
>> linkers (LLD).
>> Message-ID:
>> <CABQ7ENL+eZDSRJe9Y2AHJHwNaW+icHDgu_HhbxuHQsM=MvbMGw at mail.gm
>> ail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> An old co-worker told me that writing a dwarf support library was the most
>> painful experience of his life due to the confusing standards documents,
>> so
>> it's not surprising DWARF5 is going slow.
>>
>> GNOMETOYS
>>
>> On Mon, Dec 4, 2017 at 12:49 PM, Robinson, Paul via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>> > Thanks for providing the experimental data! It clearly shows the value
>> of
>> > type sections in DWARF.
>> >
>> > Regarding why type sections are off by default, aside from the issue of
>> > consumers needing to understand them, there is a size penalty to type
>> > sections that becomes more evident in smaller projects (meaning, fewer
>> > compilation units). The size penalty can be balanced against the
>> amount of
>> > deduplication for a net win, if you have enough duplicates that you can
>> > eliminate. But it is a tradeoff.
>> >
>> > In Sony's case, it is not uncommon for studios to do what are called
>> > "unity" builds, where you have basically one master .cpp file that does
>> > #include of each other .cpp file, giving you an LTO-like build. In this
>> > case the debug-info production will automatically produce only one copy
>> of
>> > each type, and so using type sections would probably make the net debug
>> > info bigger. And of course an LTO build will deduplicate type info at
>> the
>> > metadata level, with a similar effect.
>> >
>> > So, I think whether type sections help or hurt will depend on how a
>> > particular project's build procedure is set up. Clang/LLVM are set up
>> to
>> > do lots of smaller compilations and link them all together, in a fairly
>> > traditional model, and that is where type sections will provide the most
>> > benefit. Your data, then, is essentially for a best-case scenario.
>> Other
>> > kinds of projects will not benefit as much.
>> >
>> >
>> >
>> > Regarding DWARF 5 and emitting type sections into the .debug_info
>> section
>> > rather than the .debug_types section: The work to support DWARF 5 in
>> LLVM
>> > has not gotten very far yet. Conforming to the standard in this
>> respect is
>> > certainly on my list, however there are other features that Sony
>> considers
>> > higher priority. If you or someone else wants to contribute that
>> feature
>> > sooner, that would be excellent! Otherwise, we will get to it in due
>> time.
>> >
>> > Thanks,
>> >
>> > --paulr
>> >
>> >
>> >
>> > *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf
>> Of *George
>> > Rimar via llvm-dev
>> > *Sent:* Monday, December 04, 2017 7:11 AM
>> > *To:* llvm-dev at lists.llvm.org
>> > *Subject:* [llvm-dev] [RFC] - Deduplication of debug information in
>> > linkers (LLD).
>> >
>> >
>> >
>> > Hi all !
>> >
>> >
>> >
>> > We have an issue with LLD, it is "relocation R_X86_64_32 out of range"
>> > (PR31109)
>> >
>> > which occurs during resolving relocations in debug sections. It looks
>> > happens
>> >
>> > because .debug_info section can be too large sometimes and 32x
>> relocation
>> > is not enough
>> >
>> > to represent the value. One of possible solutions looks to be to
>> > deduplicate information
>> >
>> > to reduce .debug_info size.
>> >
>> > The rest of mail contains information about experiments I did, the
>> > obtained results and
>> >
>> > some questions and suggestions as well.
>> >
>> >
>> >
>> > I was investigating idea to deduplicate debug types information. Idea is
>> > described at
>> >
>> > p276 of DWARF4 specification (http://www.dwarfstd.org/doc/DWARF4.pdf).
>> It
>> > suggests
>> >
>> > to split types information out of .debug_info and emit multiple
>> > .debug_types sections
>> >
>> > with use of COMDATs. Both clang and gcc I tested implements
>> > -fdebug-types-section flag for that:
>> >
>> >
>> >
>> > -fdebug-types-section, -fno-debug-types-section
>> >
>> > Place debug types in their own section (ELF Only)
>> >
>> > gcc's description is here: https://gcc.gnu.org/onlinedocs
>> /gcc-6.4.0/gcc/
>> > Debugging-Options.html#Debugging-Options.
>> >
>> >
>> >
>> > This flag is disabled by default. I compared clang binaries to see the
>> > difference
>> >
>> > with and without the linker side optimisation.
>> >
>> > 1) Clang built with -g has size of 1.7 GB, .debug_info section size is
>> > 894.5 Mb.
>> >
>> > 2) Clang built with -g -fdebug-types-section has size of 1.0 GB.
>> >
>> > .debug_types size is 26.267 MB, .debug_info size is 227.7 MB.
>> >
>> >
>> >
>> > Difference is huge and I believe shows (though probably for most of
>> > readers here it was
>> >
>> > already obvious) that optimization can be useful. Though
>> > -fdebug-types-section is disabled by default.
>> >
>> > Looks it was initially disabled because not all of DWARF consumers were
>> > aware of .debug_types section.
>> >
>> >
>> >
>> > Now in 2017 situation is different. I think most of DWARF consumers
>> knows
>> > about .debug_types, but:
>> >
>> > 1) DWARF5 specification explicitly eliminates the .debug_types section
>> > introduced in DWARF4:
>> >
>> > p8, "1.4 Changes from Version 4 to Version 5"
>> http://dwarfstd.org/doc/
>> > DWARF5.pdf
>> >
>> > 2) Instead of emiting multiple .debug_types it suggests to emit multiple
>> > .debug_info COMDAT
>> >
>> > sections. (p375, p376).
>> >
>> >
>> >
>> > And it seems currently there is no way to make clang to emit multiple
>> > .debug_info with type information
>> >
>> > like DWARF5 suggests. I tried command line below:
>> >
>> > -g -fdebug-types-section -gdwarf-5
>> >
>> > It still emits .debug_types and does not look there is a flag for
>> emiting
>> > multiple .debug_info.
>> >
>> > Looking at whole LLVM code (lib/mc, lib/CodeGen) actually it seems it is
>> > just always assumed .debug_info is
>> >
>> > a unique section in object.
>> >
>> > (also not sure why clang emits .debug_types when -gdwarf-5 flag is set,
>> as
>> > this section is incompatible with v5,
>> >
>> > probably it is a bug).
>> >
>> >
>> >
>> > So my questions are following:
>> >
>> > 1) Do we want to try to implement multiple .debug_info approach ? As it
>> > seems can be very useful sometimes.
>> >
>> > 2) For now in LLD may be we may want to extend our error message from
>> > "relocation X out of range" to something
>> >
>> > suggesting to use -fdebug-types-section (only for relocations in
>> debug
>> > sections) ?
>> >
>> > 3) Why -fdebug-types-section is disabled by default ?
>> >
>> >
>> >
>> > Best regards,
>> > George | Developer | Access Softek, Inc
>> >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >
>> >
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>> ------------------------------
>>
>> Message: 5
>> Date: Mon, 4 Dec 2017 15:29:48 -0600
>> From: Dounia Khaldi via llvm-dev <llvm-dev at lists.llvm.org>
>> To: llvm-dev <llvm-dev at lists.llvm.org>
>> Subject: [llvm-dev] Adding a string-argument Intrinsic
>> Message-ID:
>> <CAEL=PfEZA0PYBVhLk8aEiD-+=DgGfpwK70ahaLFw2HQUSL4Tqw at mail.gm
>> ail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> hello,
>>
>> Is there a way to add an intrinsic that takes a string as argument?
>>
>> If yes, what should be the second value provided to the macro //
>> BUILTIN(__builtin_dummy, "v?", "n")
>> in tools/clang/include/clang/Basic/BuiltinsX86.def
>>
>> Also, what should be the type passed in include/llvm/IR/IntrinsicsX86.td
>> def dummy : GCCBuiltin<"__builtin_dummy">,
>> Intrinsic<[], [llvm_???_ty], [IntrArgMemOnly] /* , "llvm.dummy" */>;
>>
>>
>> Thanks,
>> Dounia
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>>
>> ------------------------------
>>
>> Message: 6
>> Date: Mon, 4 Dec 2017 14:38:15 -0700
>> From: Jonathan Roelofs via llvm-dev <llvm-dev at lists.llvm.org>
>> To: Dounia Khaldi <khaldi.dounia at gmail.com>, llvm-dev
>> <llvm-dev at lists.llvm.org>
>> Subject: Re: [llvm-dev] Adding a string-argument Intrinsic
>> Message-ID: <b3b4af89-74f6-f330-7aac-96364490e6b7 at codesourcery.com>
>> Content-Type: text/plain; charset="utf-8"; format=flowed
>>
>>
>>
>> On 12/4/17 2:29 PM, Dounia Khaldi via llvm-dev wrote:
>> > hello,
>> >
>> > Is there a way to add an intrinsic that takes a string as argument?
>>
>> Have a look at __builtin_annotation
>>
>>
>> Jon
>>
>> >
>> > If yes, what should be the second value provided to the macro //
>> > BUILTIN(__builtin_dummy, "v?", "n")
>> > in tools/clang/include/clang/Basic/BuiltinsX86.def
>> >
>> > Also, what should be the type passed in include/llvm/IR/IntrinsicsX86.
>> td
>> > def dummy : GCCBuiltin<"__builtin_dummy">,
>> > Intrinsic<[], [llvm_???_ty], [IntrArgMemOnly] /* , "llvm.dummy"
>> */>;
>> >
>> >
>> > Thanks,
>> > Dounia
>> >
>> >
>> >
>> >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >
>>
>> --
>> Jon Roelofs
>> jonathan at codesourcery.com
>> CodeSourcery / Mentor Embedded / Siemens
>>
>>
>> ------------------------------
>>
>> Message: 7
>> Date: Mon, 04 Dec 2017 13:44:15 -0800
>> From: Vedant Kumar via llvm-dev <llvm-dev at lists.llvm.org>
>> To: llvm-dev <llvm-dev at lists.llvm.org>
>> Subject: [llvm-dev] Passes to add/validate synthetic debug info
>> Message-ID: <5851F5DA-4917-44DB-AB14-32EC70E6E591 at apple.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> Hi,
>>
>> I've prototyped a pair of passes which 1) add synthetic debug info to a
>> Module and 2) determine how much of that info is lost. The idea is to make
>> it easier to write targeted test cases for debug info preservation. For
>> example, here is a quick way to test that Mem2Reg doesn't drop debug info
>> from one test input:
>>
>> > ; RUN: opt < %s -debugify -mem2reg -check-debugify -S 2>&1 | FileCheck
>> %s
>> > ; CHECK: CheckDebugify: PASS
>>
>> So far, I've used this utility to identify problems in LSR and
>> instcombine (haven't gotten around to filing bugs yet). There's some more
>> discussion about this utility on the thread "RFC: [GlobalISel] Towards a
>> generic MI combiner framework", where Amara and Daniel suggested trying
>> something similar at the MI level.
>>
>> I've put the passes up for review here https://reviews.llvm.org/D40512 <
>> https://reviews.llvm.org/D40512>. I just wanted to ping llvm-dev to
>> raise awareness about the proposed passes, and to see if anyone in the
>> community has concerns/feedback.
>>
>> thanks,
>> vedant
>> -------------- next part --------------
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>>
>> ------------------------------
>>
>> Message: 8
>> Date: Mon, 4 Dec 2017 14:18:37 -0800
>> From: Davide Italiano via llvm-dev <llvm-dev at lists.llvm.org>
>> To: Vedant Kumar <vsk at apple.com>
>> Cc: llvm-dev <llvm-dev at lists.llvm.org>
>> Subject: Re: [llvm-dev] Passes to add/validate synthetic debug info
>> Message-ID:
>> <CACYV=-E=a-XRyE-Mi0SbT_WiTR6wdaGwvUetffDeVGzd0pYUXw at mail.gm
>> ail.com>
>> Content-Type: text/plain; charset="UTF-8"
>>
>> On Mon, Dec 4, 2017 at 1:44 PM, Vedant Kumar <vsk at apple.com> wrote:
>> > Hi,
>> >
>> > I've prototyped a pair of passes which 1) add synthetic debug info to a
>> > Module and 2) determine how much of that info is lost. The idea is to
>> make
>> > it easier to write targeted test cases for debug info preservation. For
>> > example, here is a quick way to test that Mem2Reg doesn't drop debug
>> info
>> > from one test input:
>> >
>> > ; RUN: opt < %s -debugify -mem2reg -check-debugify -S 2>&1 | FileCheck
>> %s
>> > ; CHECK: CheckDebugify: PASS
>> >
>> >
>> > So far, I've used this utility to identify problems in LSR and
>> instcombine
>> > (haven't gotten around to filing bugs yet). There's some more discussion
>> > about this utility on the thread "RFC: [GlobalISel] Towards a generic MI
>> > combiner framework", where Amara and Daniel suggested trying something
>> > similar at the MI level.
>> >
>> > I've put the passes up for review here https://reviews.llvm.org/D40512.
>> I
>> > just wanted to ping llvm-dev to raise awareness about the proposed
>> passes,
>> > and to see if anyone in the community has concerns/feedback.
>> >
>> > thanks,
>> > vedant
>>
>> After you addressed all my comments, this is pretty close to me. I'll
>> take another look today or tomorrow but I'm confident we can iterate
>> in tree.
>> In other words, +1 from me (you may want to wait a week or so before
>> committing so that people have a chance to take a look).
>>
>>
>> --
>> Davide
>>
>> "There are no solved problems; there are only problems that are more
>> or less solved" -- Henri Poincare
>>
>>
>> ------------------------------
>>
>> Message: 9
>> Date: Mon, 04 Dec 2017 22:59:22 +0000
>> From: Eric Christopher via llvm-dev <llvm-dev at lists.llvm.org>
>> To: UE US <uexplorer666 at gmail.com>
>> Cc: "llvm-dev at lists.llvm.org" <llvm-dev at lists.llvm.org>, George Rimar
>> <grimar at accesssoftek.com>
>> Subject: Re: [llvm-dev] [RFC] - Deduplication of debug information in
>> linkers (LLD).
>> Message-ID:
>> <CALehDX6_O7Vw9uftv5Hkpkaje1iVq6H66NZDDD+efGvHFpvOaw at mail.gm
>> ail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> This isn't a particularly productive email - especially as a number of
>> people on this list are current contributors to the standard. Mostly
>> dwarf5
>> support is lined up behind one of us having the spare cycles to implement
>> it rather than anything else FWIW :)
>>
>> That said, if you have specific feedback about confusing items I'm
>> definitely happy to help figure out:
>>
>> a) some better way to say it,
>> b) some other implementation to avoid it being confusing
>>
>> Having partially implemented a couple of readers and writers at this point
>> I agree that it's not the friendliest of documents, but sometimes being
>> inside of it makes it harder to see where it's causing issues.
>>
>> Thanks!
>>
>> -eric
>>
>> On Mon, Dec 4, 2017 at 1:23 PM UE US via llvm-dev <
>> llvm-dev at lists.llvm.org>
>> wrote:
>>
>> > An old co-worker told me that writing a dwarf support library was the
>> most
>> > painful experience of his life due to the confusing standards
>> documents, so
>> > it's not surprising DWARF5 is going slow.
>> >
>> > GNOMETOYS
>> >
>> > On Mon, Dec 4, 2017 at 12:49 PM, Robinson, Paul via llvm-dev <
>> > llvm-dev at lists.llvm.org> wrote:
>> >
>> >> Thanks for providing the experimental data! It clearly shows the value
>> >> of type sections in DWARF.
>> >>
>> >> Regarding why type sections are off by default, aside from the issue of
>> >> consumers needing to understand them, there is a size penalty to type
>> >> sections that becomes more evident in smaller projects (meaning, fewer
>> >> compilation units). The size penalty can be balanced against the
>> amount of
>> >> deduplication for a net win, if you have enough duplicates that you can
>> >> eliminate. But it is a tradeoff.
>> >>
>> >> In Sony's case, it is not uncommon for studios to do what are called
>> >> "unity" builds, where you have basically one master .cpp file that does
>> >> #include of each other .cpp file, giving you an LTO-like build. In
>> this
>> >> case the debug-info production will automatically produce only one
>> copy of
>> >> each type, and so using type sections would probably make the net debug
>> >> info bigger. And of course an LTO build will deduplicate type info at
>> the
>> >> metadata level, with a similar effect.
>> >>
>> >> So, I think whether type sections help or hurt will depend on how a
>> >> particular project's build procedure is set up. Clang/LLVM are set up
>> to
>> >> do lots of smaller compilations and link them all together, in a fairly
>> >> traditional model, and that is where type sections will provide the
>> most
>> >> benefit. Your data, then, is essentially for a best-case scenario.
>> Other
>> >> kinds of projects will not benefit as much.
>> >>
>> >>
>> >>
>> >> Regarding DWARF 5 and emitting type sections into the .debug_info
>> section
>> >> rather than the .debug_types section: The work to support DWARF 5 in
>> LLVM
>> >> has not gotten very far yet. Conforming to the standard in this
>> respect is
>> >> certainly on my list, however there are other features that Sony
>> considers
>> >> higher priority. If you or someone else wants to contribute that
>> feature
>> >> sooner, that would be excellent! Otherwise, we will get to it in due
>> time.
>> >>
>> >> Thanks,
>> >>
>> >> --paulr
>> >>
>> >>
>> >>
>> >> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf
>> Of *George
>> >> Rimar via llvm-dev
>> >> *Sent:* Monday, December 04, 2017 7:11 AM
>> >> *To:* llvm-dev at lists.llvm.org
>> >> *Subject:* [llvm-dev] [RFC] - Deduplication of debug information in
>> >> linkers (LLD).
>> >>
>> >>
>> >>
>> >> Hi all !
>> >>
>> >>
>> >>
>> >> We have an issue with LLD, it is "relocation R_X86_64_32 out of range"
>> >> (PR31109)
>> >>
>> >> which occurs during resolving relocations in debug sections. It looks
>> >> happens
>> >>
>> >> because .debug_info section can be too large sometimes and 32x
>> relocation
>> >> is not enough
>> >>
>> >> to represent the value. One of possible solutions looks to be to
>> >> deduplicate information
>> >>
>> >> to reduce .debug_info size.
>> >>
>> >> The rest of mail contains information about experiments I did, the
>> >> obtained results and
>> >>
>> >> some questions and suggestions as well.
>> >>
>> >>
>> >>
>> >> I was investigating idea to deduplicate debug types information. Idea
>> is
>> >> described at
>> >>
>> >> p276 of DWARF4 specification (http://www.dwarfstd.org/doc/DWARF4.pdf).
>> >> It suggests
>> >>
>> >> to split types information out of .debug_info and emit multiple
>> >> .debug_types sections
>> >>
>> >> with use of COMDATs. Both clang and gcc I tested implements
>> >> -fdebug-types-section flag for that:
>> >>
>> >>
>> >>
>> >> -fdebug-types-section, -fno-debug-types-section
>> >>
>> >> Place debug types in their own section (ELF Only)
>> >>
>> >> gcc's description is here:
>> >> https://gcc.gnu.org/onlinedocs/gcc-6.4.0/gcc/Debugging-Optio
>> ns.html#Debugging-Options
>> >> .
>> >>
>> >>
>> >>
>> >> This flag is disabled by default. I compared clang binaries to see the
>> >> difference
>> >>
>> >> with and without the linker side optimisation.
>> >>
>> >> 1) Clang built with -g has size of 1.7 GB, .debug_info section size is
>> >> 894.5 Mb.
>> >>
>> >> 2) Clang built with -g -fdebug-types-section has size of 1.0 GB.
>> >>
>> >> .debug_types size is 26.267 MB, .debug_info size is 227.7 MB.
>> >>
>> >>
>> >>
>> >> Difference is huge and I believe shows (though probably for most of
>> >> readers here it was
>> >>
>> >> already obvious) that optimization can be useful. Though
>> >> -fdebug-types-section is disabled by default.
>> >>
>> >> Looks it was initially disabled because not all of DWARF consumers were
>> >> aware of .debug_types section.
>> >>
>> >>
>> >>
>> >> Now in 2017 situation is different. I think most of DWARF consumers
>> knows
>> >> about .debug_types, but:
>> >>
>> >> 1) DWARF5 specification explicitly eliminates the .debug_types section
>> >> introduced in DWARF4:
>> >>
>> >> p8, "1.4 Changes from Version 4 to Version 5"
>> >> http://dwarfstd.org/doc/DWARF5.pdf
>> >>
>> >> 2) Instead of emiting multiple .debug_types it suggests to emit
>> multiple
>> >> .debug_info COMDAT
>> >>
>> >> sections. (p375, p376).
>> >>
>> >>
>> >>
>> >> And it seems currently there is no way to make clang to emit multiple
>> >> .debug_info with type information
>> >>
>> >> like DWARF5 suggests. I tried command line below:
>> >>
>> >> -g -fdebug-types-section -gdwarf-5
>> >>
>> >> It still emits .debug_types and does not look there is a flag for
>> emiting
>> >> multiple .debug_info.
>> >>
>> >> Looking at whole LLVM code (lib/mc, lib/CodeGen) actually it seems it
>> is
>> >> just always assumed .debug_info is
>> >>
>> >> a unique section in object.
>> >>
>> >> (also not sure why clang emits .debug_types when -gdwarf-5 flag is set,
>> >> as this section is incompatible with v5,
>> >>
>> >> probably it is a bug).
>> >>
>> >>
>> >>
>> >> So my questions are following:
>> >>
>> >> 1) Do we want to try to implement multiple .debug_info approach ? As it
>> >> seems can be very useful sometimes.
>> >>
>> >> 2) For now in LLD may be we may want to extend our error message from
>> >> "relocation X out of range" to something
>> >>
>> >> suggesting to use -fdebug-types-section (only for relocations in
>> debug
>> >> sections) ?
>> >>
>> >> 3) Why -fdebug-types-section is disabled by default ?
>> >>
>> >>
>> >>
>> >> Best regards,
>> >> George | Developer | Access Softek, Inc
>> >>
>> >> _______________________________________________
>> >> LLVM Developers mailing list
>> >> llvm-dev at lists.llvm.org
>> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >>
>> >>
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >
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>>
>> _______________________________________________
>> llvm-dev mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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>>
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>> *****************************************
>>
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