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

Fri May 10 23:09:29 PDT 2019

Attached a repro.cc from creduce. Repro is just:
$ cat repro.cc
struct b {
  char aa;
};
struct __attribute__((__packed__)) d {
  char : 84211;
  char ak : 1;
  int al : 32;
  int am : 32;
  char an : 5;
  char : 5;
  char ap : 5;
  short c : 6;
  int aa : 27;
  int at : 32;
  int a;
  void e();
};
class f {
  void g(const b &);
  long az[];
};
void f::g(const b &h) {
  d a;
  a.ak = a.al = a.am = a.an = a.ap = a.c = a.aa = h.aa;
  a.at = az[0];
  a.e();
}
$ clang++ -O2 -fsanitize=address -o repro.o -c repro.cc
And I just noticed that clang w/ debug prints this before the stack:

clang-9: $SRC/llvm/lib/CodeGen/MachineTraceMetrics.cpp:639: (anonymous
namespace)::DataDep::DataDep(const llvm::MachineRegisterInfo *, unsigned
int, unsigned int): Assertion `!DefI.atEnd() && "Register has no defs"'
failed.

creduce is going a little more slowly on the code that crashed in "Live
Variable Analysis", but I'll leave that going over the weekend. Hope this
initial test case helps a bit.

*From: *Florian Hahn <flo at fhahn.com>
*Date: *Fri, May 10, 2019 at 4:26 PM
*To: *Jordan Rupprecht
*Cc: *llvm-commits

>
> On 11 May 2019, at 00:22, Jordan Rupprecht <rupprecht at google.com> wrote:
>
> Reverted in r360481. I have creduce going on the Machine InstCombiner
> crash and down to "only" 7000 lines, so I think it will finish before I
> leave today.
>
> There were some crashes in other places (i.e. I don't think the bug is in
> this patch, it's just revealing bugs in other places), so I'll have to see
> if those reduce to the same thing -- I'll check that out next week.
>
> Sorry for the inconvenience!
>
>
> No worries, thanks for letting me know. I’m curious what the problem with
> the machine combiner is.
>
> Cheers
>
> *From: *Jordan Rupprecht <rupprecht at google.com>
> *Date: *Fri, May 10, 2019 at 3:28 PM
> *To: *Florian Hahn
> *Cc: *llvm-commits
>
> 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.
>>>>
>>>>
>>>> _______________________________________________
>>>> llvm-commits mailing list
>>>> llvm-commits at lists.llvm.org
>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>>>>
>>>
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