Remove function from module

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#1

How correctly remove function from module?
For example:

int f1(int x) {
…
a = f2(smth);
…
}
int f2 (int y) {
…
b = f1(smth);
…}

I need delete from module both f1 and f2. They haven’t uses in other part of module, but I can’t delete them with eraseFromParent, because they are use each other.

Yours sincerely,
Kadysev Mikhail

#2

Михаил wrote:

How correctly remove function from module?
For example:

int f1(int x) {
...
a = f2(smth);
...
}
int f2 (int y) {
...
b = f1(smth);
...
}

I need delete from module both f1 and f2. They haven't uses in other
part of module, but I can't delete them with eraseFromParent, because
they are use each other.

Call X->replaceAllUsesWith(UndefValue::get(X->getType)) before calling X->eraseFromParent().

Nick

#3

Hi Михаил,

You can also use GVExtractionPass:

  if (!strcmp(argv[1], "pass"))
  {
    PassManager manager;
    manager.add(new TargetData(m.get()));
    
    // Delete functions specified in list of functions.
    vector<GlobalValue*> functions;
    functions.push_back(m.get()->getFunction("f1"));
    functions.push_back(m.get()->getFunction("f2"));
    manager.add(createGVExtractionPass(functions, true));

    // Delete unreachable globals.
    manager.add(createGlobalDCEPass());
    
    // Remove dead debug info.
    manager.add(createStripDeadDebugInfoPass());
    
    // Remove dead func decls.
    manager.add(createStripDeadPrototypesPass());

    manager.run(*m.get());
  }

  if (!strcmp(argv[1], "manual"))
  {
    Function* f1 = m.get()->getFunction("f1");
    Function* f2 = m.get()->getFunction("f2");
    
    f1->replaceAllUsesWith(UndefValue::get((Type*)f1->getType()));
    f2->replaceAllUsesWith(UndefValue::get((Type*)f2->getType()));

    f1->eraseFromParent();
    f2->eraseFromParent();
  }

- D.

makefile (388 Bytes)

test.c (98 Bytes)

test.ll (1.71 KB)

transform.cxx (1.83 KB)

#4

Thanks, but I replaceAllUsesWith() - works well, but I still get bug in eraseFromParent():

While deleting: i32 (%class.B*, i32)* %_ZN1B1xEi
An asserting value handle still pointed to this value!
UNREACHABLE executed at /Users/neonomaly/LLVM/LLVM/lib/VMCore/Value.cpp:561!

Yours sincerely,
Kadysev Mikhail

21.04.2012, в 23:45, Nick Lewycky написал(а):

#5

Could you reproduce this assertion with my test program?

22 ÁÐÒÅÌÑ 2012šÇ. 0:09 ÐÏÌØÚÏ×ÁÔÅÌØ íÉÈÁÉÌ <neonomaly.x@gmail.com> ÎÁÐÉÓÁÌ:

#6

It also occurs on several (different) test cases. I have founded that assershion rises in void ValueHandleBase::ValueIsDeleted(Value *V);

Code from function:

// All callbacks, weak references, and assertingVHs should be dropped by now.
if (V->HasValueHandle) {
#ifndef NDEBUG // Only in +Asserts mode…
dbgs() << “While deleting: " << *V->getType() << " %” << V->getNameStr()
<< “\n”;
if (pImpl->ValueHandles[V]->getKind() == Assert)
llvm_unreachable(“An asserting value handle still pointed to this
" value!”);

#endif
llvm_unreachable(“All references to V were not removed?”);
}

Yours sincerely,
Kadysev Mikhail

22.04.2012, в 1:41, Dmitry N. Mikushin написал(а):

#7

íÉÈÁÉÌ wrote:

Thanks, but I replaceAllUsesWith() - works well, but I still get bug in
eraseFromParent():

While deleting: i32 (%class.B*, i32)* %_ZN1B1xEi
An asserting value handle still pointed to this value!
UNREACHABLE executed at /Users/neonomaly/LLVM/LLVM/lib/VMCore/Value.cpp:561!

The replaceAllUsesWith + eraseFromParent pattern remains correct, but there's more to the story than the parts we've focused on. This error means that there's some other code that is holding a pointer to the function you tried to delete, but is using AssertingVH to do so, so as to catch errors exactly like this producing a dangling pointer.

The error message doesn't tell us who owns the AssertingVH (indeed, the asserting-vh doesn't know, much like a pointer doesn't know who owns it).

So, under what circumstance are you doing this deletion? Is it inside a FunctionPass, or another kind of Pass? Are you using AssertingVH's or calling other code that is? Such as ValueMap's, or some llvm analysis pass which stores an AssertingVH?

Nick

#8

It is ModulePass with AnalysisUsage of CallGraph

Yours sincerely,
Kadysev Mikhail

22.04.2012, в 5:20, Nick Lewycky написал(а):

#9

Михаил wrote:

It is ModulePass with AnalysisUsage of CallGraph

Ah, then you'll need to update the CallGraph first. Use "CG.removeFunctionFromModule(F);" before deleting it.

Nick

#10

Thanks.

I try to delete function like this (rta_IsFunctionVisited.find - set of good functions) :

// delete dead functions
for (Module::iterator Fx = M->begin(), FE = M->end(); Fx!=FE; Fx++) {
if (rta_IsFunctionVisited.find(Fx)==rta_IsFunctionVisited.end()) {
Fx->replaceAllUsesWith(UndefValue::get(Fx->getType()));
}
}

for (CallGraph::iterator CGN = CG.begin(); CGN!=CG.end(); CGN++) {
if (rta_IsFunctionVisited.find(CGN->second->getFunction())==rta_IsFunctionVisited.end()) {
CGN->second->removeAllCalledFunctions();
}
}

for (Module::iterator Fx = M->begin(), FE = M->end(); Fx!=FE;) {
if (rta_IsFunctionVisited.find(Fx)==rta_IsFunctionVisited.end()) {
CallGraphNode *CGN = CG.getOrInsertFunction(Fx);
CG.removeFunctionFromModule(Fx);
wasChanged=true;
Fx=M->begin();
} else Fx++;
}

return true;

But I still have a bug:

opt(63981) malloc: *** error for object 0x7ff1394050a0: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug
0 libLLVM-3.0.dylib 0x00000001082d7605 _ZL15PrintStackTracePv + 53
1 libLLVM-3.0.dylib 0x00000001082d7c6c _ZL13SignalHandleri + 364
2 libsystem_c.dylib 0x00007fff9152dcfa _sigtramp + 26
3 libsystem_c.dylib 0x00007fff66d6a878 _sigtramp + 18446744072996768664
4 libsystem_c.dylib 0x00007fff9152b84c free + 389
5 libLLVM-3.0.dylib 0x00000001083536b0 __gnu_cxx::new_allocator<std::pair<llvm::WeakVH, llvm::CallGraphNode*> >::deallocate(std::pair<llvm::WeakVH, llvm::CallGraphNode*>, unsigned long) + 32
6 libLLVM-3.0.dylib 0x000000010835360e std::_Vector_base<std::pair<llvm::WeakVH, llvm::CallGraphNode>, std::allocator<std::pair<llvm::WeakVH, llvm::CallGraphNode*> > >::_M_deallocate(std::pair<llvm::WeakVH, llvm::CallGraphNode*>, unsigned long) + 62
7 libLLVM-3.0.dylib 0x00000001083535bd std::_Vector_base<std::pair<llvm::WeakVH, llvm::CallGraphNode>, std::allocator<std::pair<llvm::WeakVH, llvm::CallGraphNode*> > >::~_Vector_base() + 45
8 libLLVM-3.0.dylib 0x0000000108353509 std::vector<std::pair<llvm::WeakVH, llvm::CallGraphNode*>, std::allocator<std::pair<llvm::WeakVH, llvm::CallGraphNode*> > >::~vector() + 105
9 libLLVM-3.0.dylib 0x0000000108353495 std::vector<std::pair<llvm::WeakVH, llvm::CallGraphNode*>, std::allocator<std::pair<llvm::WeakVH, llvm::CallGraphNode*> > >::~vector() + 21
10 libLLVM-3.0.dylib 0x000000010852be3e llvm::CallGraphNode::~CallGraphNode() + 110
11 libLLVM-3.0.dylib 0x0000000108529d55 llvm::CallGraphNode::~CallGraphNode() + 21
12 libLLVM-3.0.dylib 0x0000000108528468 llvm::CallGraph::destroy() + 264
13 libLLVM-3.0.dylib 0x00000001085295f8 (anonymous namespace)::BasicCallGraph::destroy() + 120
14 libLLVM-3.0.dylib 0x0000000108529379 (anonymous namespace)::BasicCallGraph::releaseMemory() + 25
15 libLLVM-3.0.dylib 0x0000000107bf5d93 llvm::PMDataManager::freePass(llvm::Pass*, llvm::StringRef, llvm::PassDebuggingString) + 179
16 libLLVM-3.0.dylib 0x0000000107bf5c89 llvm::PMDataManager::removeDeadPasses(llvm::Pass*, llvm::StringRef, llvm::PassDebuggingString) + 505
17 libLLVM-3.0.dylib 0x0000000107bf8ee8 llvm::MPPassManager::runOnModule(llvm::Module&) + 1016
18 libLLVM-3.0.dylib 0x0000000107bf949c llvm::PassManagerImpl::run(llvm::Module&) + 172
19 libLLVM-3.0.dylib 0x0000000107bf997d llvm::PassManager::run(llvm::Module&) + 29
20 opt 0x000000010717f057 main + 6903
21 opt 0x000000010716d7b4 start + 52
22 opt 0x0000000000000007 start + 18446744069295646855

Yours sincerely,
Kadysev Mikhail

22.04.2012, в 23:30, Nick Lewycky написал(а):