[llvm] r360171 - [DAGCombiner] Avoid creating large tokenfactors in visitTokenFactor

[Florian Hahn via llvm-commits]

Hi,

Do you have a reproducer you could share? That would be really helpful, as It looks like the problem is triggered in a downstream pass.

Cheers
Florian

> On 10 May 2019, at 23:28, Jordan Rupprecht <rupprecht at google.com> wrote:
> 
> Here's the full crash (minus the boiler plate) for the one in Machine InstCombiner:
>  #9 0x00007fb8d52cf5d2 (anonymous namespace)::DataDep::DataDep(llvm::MachineRegisterInfo const*, unsigned int, unsigned int) ${LLVM_SRC}/llvm/lib/CodeGen/MachineTraceMetrics.cpp:640:13
> #10 0x00007fb8d52cb644 getDataDeps(llvm::MachineInstr const&, llvm::SmallVectorImpl<(anonymous namespace)::DataDep>&, llvm::MachineRegisterInfo const*) ${LLVM_SRC}/llvm/lib/CodeGen/MachineTraceMetrics.cpp:672:22
> #11 0x00007fb8d52cb064 llvm::MachineTraceMetrics::Ensemble::updateDepth(llvm::MachineTraceMetrics::TraceBlockInfo&, llvm::MachineInstr const&, llvm::SparseSet<llvm::LiveRegUnit, llvm::identity<unsigned int>, unsigned char>&) ${LLVM_SRC}/llvm/lib/CodeGen/MachineTraceMetrics.cpp:788:12
> #12 0x00007fb8d52cc300 llvm::MachineTraceMetrics::Ensemble::computeInstrDepths(llvm::MachineBasicBlock const*) ${LLVM_SRC}/llvm/lib/CodeGen/MachineTraceMetrics.cpp:883:28
> #13 0x00007fb8d52cde9e llvm::MachineTraceMetrics::Ensemble::getTrace(llvm::MachineBasicBlock const*) ${LLVM_SRC}/llvm/lib/CodeGen/MachineTraceMetrics.cpp:1166:8
> #14 0x00007fb8d515ead4 (anonymous namespace)::MachineCombiner::combineInstructions(llvm::MachineBasicBlock*) ${LLVM_SRC}/llvm/lib/CodeGen/MachineCombiner.cpp:596:59
> #15 0x00007fb8d515e342 (anonymous namespace)::MachineCombiner::runOnMachineFunction(llvm::MachineFunction&) ${LLVM_SRC}/llvm/lib/CodeGen/MachineCombiner.cpp:654:16
> #16 0x00007fb8d51bf637 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) ${LLVM_SRC}/llvm/lib/CodeGen/MachineFunctionPass.cpp:73:8
> #17 0x00007fb8d47dd759 llvm::FPPassManager::runOnFunction(llvm::Function&) ${LLVM_SRC}/llvm/lib/IR/LegacyPassManager.cpp:1648:23
> #18 0x00007fb8d47ddb9f llvm::FPPassManager::runOnModule(llvm::Module&) ${LLVM_SRC}/llvm/lib/IR/LegacyPassManager.cpp:1685:16
> #19 0x00007fb8d47de305 (anonymous namespace)::MPPassManager::runOnModule(llvm::Module&) ${LLVM_SRC}/llvm/lib/IR/LegacyPassManager.cpp:1752:23
> #20 0x00007fb8d47dde45 llvm::legacy::PassManagerImpl::run(llvm::Module&) ${LLVM_SRC}/llvm/lib/IR/LegacyPassManager.cpp:1865:16
> #21 0x00007fb8d47de881 llvm::legacy::PassManager::run(llvm::Module&) ${LLVM_SRC}/llvm/lib/IR/LegacyPassManager.cpp:1896:3
> #22 0x00007fb8d117e15a (anonymous namespace)::EmitAssemblyHelper::EmitAssembly(clang::BackendAction, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream> >) ${LLVM_SRC}/clang/lib/CodeGen/BackendUtil.cpp:894:3
> 
> 
> From: Jordan Rupprecht <rupprecht at google.com>
> Date: Fri, May 10, 2019 at 12:58 PM
> To: Florian Hahn
> Cc: llvm-commits
> 
>> Looks like this causes some asan/msan crashes (or in some cases, test failure/miscompiles). I'll see if I can get a crash with debug+asserts enabled. In release mode, it's crashing during Machine InstCombiner/Live Variable Analysis for different repros.
>> 
>> 
>> From: Florian Hahn via llvm-commits <llvm-commits at lists.llvm.org>
>> Date: Tue, May 7, 2019 at 9:45 AM
>> To: <llvm-commits at lists.llvm.org>
>> 
>>> Author: fhahn
>>> Date: Tue May  7 09:47:27 2019
>>> New Revision: 360171
>>> 
>>> URL: http://llvm.org/viewvc/llvm-project?rev=360171&view=rev
>>> Log:
>>> [DAGCombiner] Avoid creating large tokenfactors in visitTokenFactor
>>> 
>>> When simplifying TokenFactors, we potentially iterate over all
>>> operands of a large number of TokenFactors. This causes quadratic
>>> compile times in some cases and the large token factors cause additional
>>> scalability problems elsewhere.
>>> 
>>> This patch adds some limits to the number of nodes explored for the
>>> cases mentioned above.
>>> 
>>> Reviewers: niravd, spatel, craig.topper
>>> 
>>> Reviewed By: niravd
>>> 
>>> Differential Revision: https://reviews.llvm.org/D61397
>>> 
>>> Modified:
>>>     llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
>>> 
>>> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=360171&r1=360170&r2=360171&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
>>> +++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Tue May  7 09:47:27 2019
>>> @@ -1792,8 +1792,9 @@ SDValue DAGCombiner::visitTokenFactor(SD
>>>    TFs.push_back(N);
>>> 
>>>    // Iterate through token factors.  The TFs grows when new token factors are
>>> -  // encountered.
>>> -  for (unsigned i = 0; i < TFs.size(); ++i) {
>>> +  // encountered. Limit number of nodes to inline, to avoid quadratic compile
>>> +  // times.
>>> +  for (unsigned i = 0; i < TFs.size() && Ops.size() <= 2048; ++i) {
>>>      SDNode *TF = TFs[i];
>>> 
>>>      // Check each of the operands.
>>> 
>>> 
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