[llvm] r314435 - [JumpThreading] Preserve DT and LVI across the pass

Wed Oct 4 13:12:25 PDT 2017

I have just pushed two patches into Phabricator:
Take two of the DT/LVI patch:

https://reviews.llvm.org/D38558

A patch to place DT/LVI preservation under a flag:

https://reviews.llvm.org/D38559

Jakub, I too am planning on doing some profiling later this week. I would
like to collaborate to minimize duplicated efforts.

On Wed, Oct 4, 2017 at 12:01 PM, Jakub (Kuba) Kuderski via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> I will try to profile the sqlite compilation later this week. It is not
> easy to come up with some benchmarks for the batch updater, and because of
> that it hasn't really been optimized yet. JumpThreading seems to be the
> first pass to put significant pressure on the incremental updater, so it'd
> be valuable to learn how much faster we can get there.
>
> On Wed, Oct 4, 2017 at 12:47 PM, Michael Zolotukhin <mzolotukhin at apple.com
> > wrote:
>
>>
>> On Oct 4, 2017, at 9:25 AM, Daniel Berlin <dberlin at dberlin.org> wrote:
>>
>> +jakub for real.
>>
>> On Wed, Oct 4, 2017 at 9:21 AM, Daniel Berlin <dberlin at dberlin.org>
>> wrote:
>>
>>> +jakub
>>>
>>> I don't think preservation should be controlled by a flag.  That seems
>>> like not a great path forward.
>>> Either we should make it fast enough, or we should give up :)
>>>
>>> Do you have any profiles on this?
>>>
>> I don’t, but it seems pretty clear what’s going on there - we do an extra
>> work (preserving DT) for no benefits (we’re recomputing it a couple of
>> passes later anyway). The pass after which it’s recomputed is SimplifyCFG,
>> and I think it would be a much bigger endeavor to teach it to account for
>> DT - so putting it under a flag for JumpThreading could help doing this
>> work incrementally.
>>
>> Michael
>>
>>
>>>
>>>
>>> On Sat, Sep 30, 2017 at 12:19 PM, Michael Zolotukhin via llvm-commits <
>>> llvm-commits at lists.llvm.org> wrote:
>>>
>>>> For the record, we also detected significant compile-time increases
>>>> caused by this patch. It caused up to 10% slow downs on sqlite3 and some
>>>> other tests from CTMark/LLVM testsuite (on O3/LTO and other optsets).
>>>>
>>>> Reproducer:
>>>>
>>>> time clang-r314435/bin/clang  -DNDEBUG -O3 -arch arm64 -isysroot
>>>> $SYSROOT -DSTDC_HEADERS=1  -DSQLITE_OMIT_LOAD_EXTENSION=1
>>>> -DSQLITE_THREADSAFE=0  -w -o sqlite3.c.o -c $TESTSUITE/CTMark/sqlite3/sqli
>>>> te3.c
>>>> real    0m20.235s
>>>> user    0m20.130s
>>>> sys     0m0.091s
>>>>
>>>> time clang-r314432/bin/clang  -DNDEBUG -O3 -arch arm64 -isysroot
>>>> $SYSROOT -DSTDC_HEADERS=1  -DSQLITE_OMIT_LOAD_EXTENSION=1
>>>> -DSQLITE_THREADSAFE=0  -w -o sqlite3.c.o -c $TESTSUITE/CTMark/sqlite3/sqli
>>>> te3.c
>>>> real    0m19.254s
>>>> user    0m19.154s
>>>> sys     0m0.094s
>>>>
>>>> JumpThreading started to consume much longer time trying to preserve
>>>> DT, but DT was still being recomputed couple of passes later. In general, I
>>>> agree that we should preserve DT and in the end it should be beneficial for
>>>> compile time too, but can we put it under a flag for now until we can
>>>> actually benefit from it?
>>>>
>>>> Thanks,
>>>> Michael
>>>>
>>>>
>>>> On Sep 30, 2017, at 5:02 AM, Daniel Jasper via llvm-commits <
>>>> llvm-commits at lists.llvm.org> wrote:
>>>>
>>>> I found other places where this Clang was running into this segfault.
>>>> Reverted for now in r314589.
>>>>
>>>> On Fri, Sep 29, 2017 at 10:19 PM, Friedman, Eli via llvm-commits <
>>>> llvm-commits at lists.llvm.org> wrote:
>>>>
>>>>> On 9/28/2017 10:24 AM, Evandro Menezes via llvm-commits wrote:
>>>>>
>>>>> Author: evandro
>>>>> Date: Thu Sep 28 10:24:40 2017
>>>>> New Revision: 314435
>>>>>
>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=314435&view=rev
>>>>> Log:
>>>>> [JumpThreading] Preserve DT and LVI across the pass
>>>>>
>>>>> JumpThreading now preserves dominance and lazy value information across the
>>>>> entire pass.  The pass manager is also informed of this preservation with
>>>>> the goal of DT and LVI being recalculated fewer times overall during
>>>>> compilation.
>>>>>
>>>>> This change prepares JumpThreading for enhanced opportunities; particularly
>>>>> those across loop boundaries.
>>>>>
>>>>> Patch by: Brian Rzycki <b.rzycki at samsung.com> <b.rzycki at samsung.com>,
>>>>>           Sebastian Pop <s.pop at samsung.com> <s.pop at samsung.com>
>>>>>
>>>>> Differential revision: https://reviews.llvm.org/D37528
>>>>>
>>>>>
>>>>> It looks like this is causing an assertion failure on the polly aosp
>>>>> buildbot (http://lab.llvm.org:8011/builders/aosp-O3-polly-before-vect
>>>>> orizer-unprofitable/builds/266/steps/build-aosp/logs/stdio):
>>>>>
>>>>> clang: /var/lib/buildbot/slaves/hexagon-build-03/aosp/llvm.src/include/llvm/Support/GenericDomTreeConstruction.h:906: static void llvm::DomTreeBuilder::SemiNCAInfo<llvm::DominatorTreeBase<llvm::BasicBlock, false> >::DeleteEdge(DomTreeT &, const BatchUpdatePtr, const NodePtr, const NodePtr) [DomTreeT = llvm::DominatorTreeBase<llvm::BasicBlock, false>]: Assertion `!IsSuccessor(To, From) && "Deleted edge still exists in the CFG!"' failed.
>>>>> #0 0x00000000014f6fc4 PrintStackTraceSignalHandler(void*) (llvm.inst/bin/clang+0x14f6fc4)
>>>>> #1 0x00000000014f72d6 SignalHandler(int) (llvm.inst/bin/clang+0x14f72d6)
>>>>> #2 0x00007f694afddd10 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x10d10)
>>>>> #3 0x00007f6949bbb267 gsignal /build/buildd/glibc-2.21/signal/../sysdeps/unix/sysv/linux/raise.c:55:0
>>>>> #4 0x00007f6949bbceca abort /build/buildd/glibc-2.21/stdlib/abort.c:91:0
>>>>> #5 0x00007f6949bb403d __assert_fail_base /build/buildd/glibc-2.21/assert/assert.c:92:0
>>>>> #6 0x00007f6949bb40f2 (/lib/x86_64-linux-gnu/libc.so.6+0x2e0f2)
>>>>> #7 0x000000000104a1dc (llvm.inst/bin/clang+0x104a1dc)
>>>>> #8 0x0000000001357fd9 llvm::JumpThreadingPass::ProcessBlock(llvm::BasicBlock*) (llvm.inst/bin/clang+0x1357fd9)
>>>>> #9 0x0000000001356e6e llvm::JumpThreadingPass::runImpl(llvm::Function&, llvm::TargetLibraryInfo*, llvm::LazyValueInfo*, llvm::AAResults*, llvm::DominatorTree*, bool, std::unique_ptr<llvm::BlockFrequencyInfo, std::default_delete<llvm::BlockFrequencyInfo> >, std::unique_ptr<llvm::BranchProbabilityInfo, std::default_delete<llvm::BranchProbabilityInfo> >) (llvm.inst/bin/clang+0x1356e6e)
>>>>> #10 0x0000000001363c49 (anonymous namespace)::JumpThreading::runOnFunction(llvm::Function&) (llvm.inst/bin/clang+0x1363c49)
>>>>> #11 0x00000000010a53c4 llvm::FPPassManager::runOnFunction(llvm::Function&) (llvm.inst/bin/clang+0x10a53c4)
>>>>> #12 0x00000000031f7376 (anonymous namespace)::CGPassManager::runOnModule(llvm::Module&) (llvm.inst/bin/clang+0x31f7376)
>>>>> #13 0x00000000010a5b05 llvm::legacy::PassManagerImpl::run(llvm::Module&) (llvm.inst/bin/clang+0x10a5b05)
>>>>> #14 0x0000000001688beb clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::DataLayout const&, llvm::Module*, clang::BackendAction, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream> >) (llvm.inst/bin/clang+0x1688beb)
>>>>> #15 0x0000000001ed7672 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (llvm.inst/bin/clang+0x1ed7672)
>>>>> #16 0x0000000002195235 clang::ParseAST(clang::Sema&, bool, bool) (llvm.inst/bin/clang+0x2195235)
>>>>> #17 0x0000000001a75628 clang::FrontendAction::Execute() (llvm.inst/bin/clang+0x1a75628)
>>>>> #18 0x0000000001a37181 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (llvm.inst/bin/clang+0x1a37181)
>>>>> #19 0x0000000001b06501 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (llvm.inst/bin/clang+0x1b06501)
>>>>> #20 0x000000000080e433 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (llvm.inst/bin/clang+0x80e433)
>>>>> #21 0x000000000080c997 main (llvm.inst/bin/clang+0x80c997)
>>>>> #22 0x00007f6949ba6a40 __libc_start_main /build/buildd/glibc-2.21/csu/libc-start.c:323:0
>>>>> #23 0x0000000000809479 _start (llvm.inst/bin/clang+0x809479)
>>>>>
>>>>> I'll try to come up with a reduced testcase this afternoon.
>>>>>
>>>>> -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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>>>>> llvm-commits at lists.llvm.org
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>>>>>
>>>>>
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>>>
>>
>>
>
>
> --
> Jakub Kuderski
>
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