[llvm-commits] PATCH: Fix AddressSanitizer to emit basic blocks in the natural order for the CFG

[Chandler Carruth]

This will in theory (hehe, see below) make many parts of LLVM work faster
where the algorithms are tuned for "normal" CFG patterns in code.
Previously ASan would create massive live ranges by inserting basic blocks
onto the end of the function.

Currently this would cause some minor regressions in performance, but that
will be fixed by a subsequent patch that attaches branch weight metadata to
the appropriate places in the generated code. These will then allow the
block placement pass to re-order the basic blocks into the optimal layout
at the very end of codegen.

Sadly, this bright and shiny future is not where we are. Applying this
patch and re-running the regression test Kostya added to PR13225 (which is
actually a repro for PR12652) the codegen time slows down **massively**.
The profile also looks quite different:

    29.03%      llc  llc                  [.] findLocalKill(unsigned int,
llvm::MachineBasicBlock*, llvm::MachineInstr*, llvm::MachineRegisterInfo*,
llvm::DenseMap<llvm::MachineInstr*, unsigned int,
llvm::DenseMapInfo<llvm::MachineInstr*> >&)



    15.41%      llc  llc                  [.] void
std::vector<llvm::MachineBasicBlock*,
std::allocator<llvm::MachineBasicBlock*>
>::_M_range_insert<std::reverse_iterator<__gnu_cxx::__normal_iterator<llvm::MachineBasicBlock**,
std::vector<llvm::MachineBasicBlock*,
std::allocator<llvm::MachineBasicBlock*> > > >
>(__gnu_cxx::__normal_iterator<llvm::MachineBasicBlock**,
std::vector<llvm::MachineBasicBlock*,
std::allocator<llvm::MachineBasicBlock*> > >,
std::reverse_iterator<__gnu_cxx::__normal_iterato
     8.05%      llc  llc                  [.]
llvm::LiveVariables::MarkVirtRegAliveInBlock(llvm::LiveVariables::VarInfo&,
llvm::MachineBasicBlock*, llvm::MachineBasicBlock*,
std::vector<llvm::MachineBasicBlock*,
std::allocator<llvm::MachineBasicBlock*> >&)



     7.80%      llc  llc                  [.]
llvm::LiveInterval::addRangeFrom(llvm::LiveRange, llvm::LiveRange*)






     6.76%      llc  llc                  [.]
llvm::LiveIntervals::handleVirtualRegisterDef(llvm::MachineBasicBlock*,
llvm::MachineBasicBlock::bundle_iterator<llvm::MachineInstr,
llvm::ilist_iterator<llvm::MachineInstr> >, llvm::SlotIndex,
llvm::MachineOperand&, unsigned int, llvm::LiveInterval&)



     4.23%      llc  llc                  [.] (anonymous
namespace)::TwoAddressInstructionPass::TryInstructionTransform(llvm::MachineBasicBlock::bundle_iterator<llvm::MachineInstr,
llvm::ilist_iterator<llvm::MachineInstr> >&,
llvm::MachineBasicBlock::bundle_iterator<llvm::MachineInstr,
llvm::ilist_iterator<llvm::MachineInstr> >&,
llvm::ilist_iterator<llvm::MachineBasicBlock>&, unsigned int, unsigned int,
unsigned int, llvm::SmallPtrSet<llvm::MachineInstr*, 8u>&)

     3.30%      llc  llc                  [.]
llvm::LiveInterval::extendIntervalEndTo(llvm::LiveRange*, llvm::SlotIndex)






     2.89%      llc  llc                  [.]
llvm::SparseBitVector<128u>::test(unsigned int)






     2.68%      llc  llc                  [.]
llvm::SparseBitVector<128u>::FindLowerBound(unsigned int)






     2.17%      llc  llc                  [.]
llvm::SparseBitVector<128u>::set(unsigned int)






     0.80%      llc  llc                  [.]
llvm::LiveVariables::HandleVirtRegUse(unsigned int,
llvm::MachineBasicBlock*, llvm::MachineInstr*)





     0.65%      llc  libc-2.13.so         [.] _int_malloc






     0.46%      llc  llc                  [.]
llvm::SelectionDAGISel::SelectCodeCommon(llvm::SDNode*, unsigned char
const*, unsigned int)





     0.42%      llc  llc                  [.]
llvm::SparseBitVector<128u>::SparseBitVectorIterator::AdvanceToNextNonZero()






     0.38%      llc  llc                  [.]
llvm::SmallPtrSetImpl::insert_imp(void const*)






     0.37%      llc  llc                  [.] (anonymous
namespace)::DAGCombiner::visit(llvm::SDNode*)





     0.37%      llc  llc                  [.]
llvm::SmallVectorImpl<llvm::LiveRange>::insert(llvm::LiveRange*,
llvm::LiveRange const&)


So, while I think this is definitely the right way to go eventually (and if
you can go ahead and review, that would be appreciated) clearly we can't
commit this until this is a bit less severe... ;]

I think making 'join' use my new merge logic may help some of these (the
addRangeFrom in particular), others look largely unrelated.

-Chandler
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