[PATCH] D20178: Fix PR26055 - LiveDebugValues is very slow

[Davide Italiano via llvm-commits]

davide added a comment.

First, let me tell you that I'm very excited about this patch. During an LTO build of medium-to-large sized C++ applications, I can clearly see this pass showing up in the profile, so I decided to benchmark it. Unfortunately, I think the patch as is introduces a regression :(

#0 0x00000000005e4398 llvm::sys::PrintStackTrace(llvm::raw_ostream&) (/home/davide/work/build-llvm/bin/lld+0x5e4398) 0x00000000005e1eee llvm::sys::RunSignalHandlers() (/home/davide/work/build-llvm/bin/lld+0x5e1eee)
#2 0x00000000005e2136 SignalHandler(int) (/home/davide/work/build-llvm/bin/lld+0x5e2136)
#3 0x00007f71573309f0 __restore_rt (/lib64/libpthread.so.0+0x109f0)
#4 0x000000000141867c (anonymous namespace)::LiveDebugValues::transferRegisterDef(llvm::MachineInstr&, llvm::SparseBitVector<128u>&, llvm::UniqueVector<(anonymous namespace)::LiveDebugValues::VarLoc> const&) [clone .isra.178] [clone .constprop.275] (/home/davide/work/build-llvm/bin/lld+0x141867c)
#5 0x000000000141a827 (anonymous namespace)::LiveDebugValues::ExtendRanges(llvm::MachineFunction&) [clone .constprop.265] (/home/davide/work/build-llvm/bin/lld+0x141a827)
#6 0x0000000001479b65 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/home/davide/work/build-llvm/bin/lld+0x1479b65)
#7 0x0000000001c3a0b2 llvm::FPPassManager::runOnFunction(llvm::Function&) (/home/davide/work/build-llvm/bin/lld+0x1c3a0b2)
#8 0x0000000001c3a41b llvm::FPPassManager::runOnModule(llvm::Module&) (/home/davide/work/build-llvm/bin/lld+0x1c3a41b)
#9 0x0000000001c39bfe llvm::legacy::PassManagerImpl::run(llvm::Module&) (/home/davide/work/build-llvm/bin/lld+0x1c39bfe)
#10 0x00000000014dae09 codegen(llvm::Module*, llvm::raw_pwrite_stream&, std::function<std::unique_ptr<llvm::TargetMachine, std::default_delete<llvm::TargetMachine> > ()>, llvm::TargetMachine::CodeGenFileType) [clone .constprop.50] (/home/davide/work/build-llvm/bin/lld+0x14dae09)
#11 0x00000000014db08a llvm::splitCodeGen(std::unique_ptr<llvm::Module, std::default_delete<llvm::Module> >, llvm::ArrayRef<llvm::raw_pwrite_stream*>, llvm::ArrayRef<llvm::raw_pwrite_stream*>, std::function<std::unique_ptr<llvm::TargetMachine, std::default_delete<llvm::TargetMachine> > ()> const&, llvm::TargetMachine::CodeGenFileType, bool) (/home/davide/work/build-llvm/bin/lld+0x14db08a)
#12 0x00000000005bb240 lld::elf::BitcodeCompiler::runSplitCodegen(std::function<std::unique_ptr<llvm::TargetMachine, std::default_delete<llvm::TargetMachine> > ()> const&) (/home/davide/work/build-llvm/bin/lld+0x5bb240)
#13 0x00000000005bc827 lld::elf::BitcodeCompiler::compile() (/home/davide/work/build-llvm/bin/lld+0x5bc827)
#14 0x000000000057ab45 lld::elf::SymbolTable<llvm::object::ELFType<(llvm::support::endianness)1, true> >::addCombinedLtoObject() (/home/davide/work/build-llvm/bin/lld+0x57ab45)
#15 0x00000000004ecfb8 void lld::elf::LinkerDriver::link<llvm::object::ELFType<(llvm::support::endianness)1, true> >(llvm::opt::InputArgList&) (/home/davide/work/build-llvm/bin/lld+0x4ecfb8)
#16 0x000000000044e7ec lld::elf::LinkerDriver::main(llvm::ArrayRef<char const*>) (/home/davide/work/build-llvm/bin/lld+0x44e7ec)
#17 0x00000000004eefbe lld::elf::link(llvm::ArrayRef<char const*>, llvm::raw_ostream&, bool) (/home/davide/work/build-llvm/bin/lld+0x4eefbe)
#18 0x000000000044dce7 main (/home/davide/work/build-llvm/bin/lld+0x44dce7)
#19 0x00007f71564ce580 __libc_start_main (/lib64/libc.so.6+0x20580)
#20 0x00000000004a03b9 _start (/home/davide/work/build-llvm/bin/lld+0x4a03b9)
Stack dump:
0.      Program arguments:

1. Running pass 'Function Pass Manager' on module 'ld-temp.o'.
2. Running pass 'Live DEBUG_VALUE analysis' on function '@_Z10iPPc'

I have limited time next week, but I'll try anyway to reduce a test case for you ASAP.


http://reviews.llvm.org/D20178