Question

I used LLVM already existent passes with no problems till I tried to use MemDepPrinter.cpp : http://llvm.org/doxygen/MemDepPrinter_8cpp_source.html . I got the following segfault:

llvm[0]: Compiling MyMemDepPrinter.cpp for Release+Asserts build (PIC)
llvm[0]: Linking Release+Asserts Loadable Module MyMemDepPrinter.so
WARNING: You're attempting to print out a bitcode file.
This is inadvisable as it may cause display problems. If
you REALLY want to taste LLVM bitcode first-hand, you
can force output with the `-f' option.

0  opt       0x08eaf9a8
1  opt       0x08eaff24
2            0xb7753400 __kernel_sigreturn + 0
3  opt       0x08c00c19 llvm::MemoryDependenceAnalysis::getNonLocalPointerDepFromBB(llvm::PHITransAddr const&, llvm::AliasAnalysis::Location const&, bool, llvm::BasicBlock*, llvm::SmallVectorImpl<llvm::NonLocalDepResult>&, llvm::DenseMap<llvm::BasicBlock*, llvm::Value*, llvm::DenseMapInfo<llvm::BasicBlock*> >&, bool) + 3673
4  opt       0x08c019aa llvm::MemoryDependenceAnalysis::getNonLocalPointerDependency(llvm::AliasAnalysis::Location const&, bool, llvm::BasicBlock*, llvm::SmallVectorImpl<llvm::NonLocalDepResult>&) + 266
5  opt       0x08bf1bed
6  opt       0x08e3415c llvm::FPPassManager::runOnFunction(llvm::Function&) + 636
7  opt       0x08e341c8 llvm::FPPassManager::runOnModule(llvm::Module&) + 56
8  opt       0x08e33de4 llvm::MPPassManager::runOnModule(llvm::Module&) + 692
9  opt       0x08e37270 llvm::PassManagerImpl::run(llvm::Module&) + 240
10 opt       0x08e37386 llvm::PassManager::run(llvm::Module&) + 38
11 opt       0x081a290f main + 6095
12 libc.so.6 0xb74604d3 __libc_start_main + 243
13 opt       0x081b8509
Stack dump:
0.  Program arguments: //home/alex/llvm/Release+Asserts/bin/opt -load //home/alex/llvm/Release+Asserts/lib/MyMemDepPrinter.so -memdep -print-memdeps //home/alex/llvm/tools/clang/woRKSPACE/Test.bc 
1.  Running pass 'Function Pass Manager' on module '//home/alex/llvm/tools/clang/woRKSPACE/Test.bc'.
2.  Running pass 'Print MemDeps of function' on function '@_Z9deadcode1i'
./run.sh: line 14:  3326 Segmentation fault      (core dumped) //home/alex/llvm/Release+Asserts/bin/opt -load //home/alex/llvm/Release+Asserts/lib/MyMemDepPrinter.so -print-memdeps //home/alex/llvm/tools/clang/woRKSPACE/Test.bc

When I am running it in GDB mode, I get:

Program received signal SIGSEGV, Segmentation fault.
0x08c00c19 in llvm::MemoryDependenceAnalysis::getNonLocalPointerDepFromBB(llvm::PHITransAddr const&, llvm::AliasAnalysis::Location const&, bool, llvm::BasicBlock*, llvm::SmallVectorImpl<llvm::NonLocalDepResult>&, llvm::DenseMap<llvm::BasicBlock*, llvm::Value*, llvm::DenseMapInfo<llvm::BasicBlock*> >&, bool) ()
(gdb) x/i $pc
=> 0x8c00c19 <_ZN4llvm24MemoryDependenceAnalysis27getNonLocalPointerDepFromBBERKNS_12PHITransAddrERKNS_13AliasAnalysis8LocationEbPNS_10BasicBlockERNS_15SmallVectorImplINS_17NonLocalDepResultEEERNS_8DenseMapIS9_PNS_5ValueENS_12DenseMapInfoIS9_EEEEb+3673>:  mov    0x10(%eax),%eax

As an update, the line problem is :

MDA.getNonLocalPointerDependency(Loc, true, LI->getParent(), NLDI);

and not the 4 arguments are the problem. All of them are defined and I can use them. I don’t have the segfault if I eliminate the line.

I think the problem is defined in a comment :

FIXME: Handle atomic/volatile loads.

Please tell me how can I solve the problem (maybe put a condition to avoid atomic/volatile loads) or if the pass works fine for you and if so, how you use it.

Thank you !

Answer 1

I saw another more recent posts, so i think i is better to try the manual dependencies. It is not the first time then there are errors in open source code. I tried to run the pass and I have the same problem. The same problem with getNonLocalPointerDependency method appears also for the other instruction types, like store, not only in the place mentioned by you.