[llvm-dev] Creating/Deleting a new instruction from LLVM IR

Ansar K.A. via llvm-dev llvm-dev at lists.llvm.org
Wed Nov 25 21:44:17 PST 2015 

Hi,

What I am trying to do is to check duplicate arithmetic instructions, if
found any, I want to delete that duplicate instruction and needed to add a
*Store *Instruction.

Code:
        Instruction* temp_Ins;
        for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
           for (BasicBlock::iterator i = b->begin(), ie = b->end(); i !=
ie; ++i) {

                     switch(curr_Ins->getOpcode()){

                              case Instruction::Add: {
                                     // Here i am keeping expression and
its address to a *Map. *Eg: *mymap[a+b]=i*
                                     // If 'a+b' is already in the list
then i am trying to delete that new duplicate instruction from LLVM IR.
                                     // following is the code i wrote for
deleting duplicate *add *instruction:
                                     temp_Ins = cast<Instruction>(i);
temp_Ins->eraseFromParent();
                              }
                     }
           }
        }

What I am doing wrong here ?

On 26 November 2015 at 09:22, Mehdi Amini <mehdi.amini at apple.com> wrote:

> Hi,
>
> On Nov 25, 2015, at 7:05 PM, Ansar K.A. via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Hi,
>
> I was trying to create a new  *Store* instruction and inserting it to
> LLVM IR (.ll) file. I found the following constructor in LLVM Manual:
>
> StoreInst::StoreInst
> <http://llvm.org/docs/doxygen/html/classllvm_1_1StoreInst.html#aa2a72f9a51b317f5b4ab8695adf59025>
> (Value <http://llvm.org/docs/doxygen/html/classllvm_1_1Value.html> * Val,
> Value <http://llvm.org/docs/doxygen/html/classllvm_1_1Value.html> * Ptr,
> Instruction
> <http://llvm.org/docs/doxygen/html/classllvm_1_1Instruction.html> *
> InsertBefore )
>
> I thought of using this. I don't know the meaning of the constructors
> arguments. What all values should be passed for creating a new *Store *Instruction
> (with an *example) *?
>
>
> How to insert this to LLVM IR? ( I saw the code snippet in LLVM
> Programming manual, I couldn't understand it. Any examples on doing the
> same? )
>
>
>
> - Val is the value you want to store.
> - Ptr is the location where you want to store the value Val.
> - InsertBefore is an optional pointer to an existing instruction, if it is
> provided the newly created instruction will be just before the provided one.
>
> Also you may want to use the IRBuilder in general to create IR, you may
> want to follow the Kaleidoscope tutorial at least once (Creating a Store is
> done chapter 7: http://llvm.org/docs/tutorial/LangImpl7.html )
>
>
> I tried to delete an instruction using:
>
>                         i->eraseFromParent();
>
>
>
> From the trace it does not seem that this call is leading to the assert.
> You’re not giving enough information about what you’re doing here. It could
> be some iterator invalidation for example.
>
> —
> Mehdi
>
>
>
>
>
>
> But it throws the following error/exception:
>
> *opt -load /home/mtech2/Documents/llvm/build/Debug+Asserts/lib/CSE.so -CSE
> <test.ll> /dev/null*
> *opt: /home/mtech2/Documents/llvm/llvm/include/llvm/Support/Casting.h:81:
> static bool llvm::isa_impl_cl<To, From*>::doit(const From*) [with To =
> llvm::Instruction; From = llvm::Instruction]: Assertion `Val && "isa<> used
> on a null pointer"' failed.*
> *#0 0x29635a5 llvm::sys::PrintStackTrace(llvm::raw_ostream&)
> /home/mtech2/Documents/llvm/llvm/lib/Support/Unix/Signals.inc:405:0*
> *#1 0x29638ba PrintStackTraceSignalHandler(void*)
> /home/mtech2/Documents/llvm/llvm/lib/Support/Unix/Signals.inc:463:0*
> *#2 0x2961eb9 llvm::sys::RunSignalHandlers()
> /home/mtech2/Documents/llvm/llvm/lib/Support/Signals.cpp:34:0*
> *#3 0x29623b1 SignalHandler(int)
> /home/mtech2/Documents/llvm/llvm/lib/Support/Unix/Signals.inc:211:0*
> *#4 0x7f190977a340 __restore_rt
> (/lib/x86_64-linux-gnu/libpthread.so.0+0x10340)*
> *#5 0x7f1908715cc9 gsignal
> /build/buildd/eglibc-2.19/signal/../nptl/sysdeps/unix/sysv/linux/raise.c:56:0*
> *#6 0x7f19087190d8 abort /build/buildd/eglibc-2.19/stdlib/abort.c:91:0*
> *#7 0x7f190870eb86 __assert_fail_base
> /build/buildd/eglibc-2.19/assert/assert.c:92:0*
> *#8 0x7f190870ec32 (/lib/x86_64-linux-gnu/libc.so.6+0x2fc32)*
> *#9 0x7f19084d9970 llvm::isa_impl_cl<llvm::Instruction,
> llvm::Instruction*>::doit(llvm::Instruction const*)
> /home/mtech2/Documents/llvm/llvm/include/llvm/Support/Casting.h:82:0*
> *#10 0x7f19084d9450 llvm::isa_impl_wrap<llvm::Instruction,
> llvm::Instruction*, llvm::Instruction*>::doit(llvm::Instruction* const&)
> /home/mtech2/Documents/llvm/llvm/include/llvm/Support/Casting.h:123:0*
> *#11 0x7f19084d89e2 llvm::isa_impl_wrap<llvm::Instruction,
> llvm::ilist_iterator<llvm::Instruction> const,
> llvm::Instruction*>::doit(llvm::ilist_iterator<llvm::Instruction> const&)
> /home/mtech2/Documents/llvm/llvm/include/llvm/Support/Casting.h:115:0*
> *#12 0x7f19084d8371 bool llvm::isa<llvm::Instruction,
> llvm::ilist_iterator<llvm::Instruction>
> >(llvm::ilist_iterator<llvm::Instruction> const&)
> /home/mtech2/Documents/llvm/llvm/include/llvm/Support/Casting.h:135:0*
> *#13 0x7f19084d7ba1 llvm::cast_retty<llvm::Instruction,
> llvm::ilist_iterator<llvm::Instruction> >::ret_type
> llvm::cast<llvm::Instruction, llvm::ilist_iterator<llvm::Instruction>
> >(llvm::ilist_iterator<llvm::Instruction>&)
> /home/mtech2/Documents/llvm/llvm/include/llvm/Support/Casting.h:230:0*
> *#14 0x7f19084d73fd (anonymous
> namespace)::CSE::runOnFunction(llvm::Function&)
> /home/mtech2/Documents/llvm/llvm/lib/Transforms/CSE/CSE.cpp:48:0*
> *#15 0x288fd1c llvm::FPPassManager::runOnFunction(llvm::Function&)
> /home/mtech2/Documents/llvm/llvm/lib/IR/LegacyPassManager.cpp:1528:0*
> *#16 0x288feaf llvm::FPPassManager::runOnModule(llvm::Module&)
> /home/mtech2/Documents/llvm/llvm/lib/IR/LegacyPassManager.cpp:1549:0*
> *#17 0x289024a (anonymous
> namespace)::MPPassManager::runOnModule(llvm::Module&)
> /home/mtech2/Documents/llvm/llvm/lib/IR/LegacyPassManager.cpp:1605:0*
> *#18 0x28909bb llvm::legacy::PassManagerImpl::run(llvm::Module&)
> /home/mtech2/Documents/llvm/llvm/lib/IR/LegacyPassManager.cpp:1708:0*
> *#19 0x2890bfb llvm::legacy::PassManager::run(llvm::Module&)
> /home/mtech2/Documents/llvm/llvm/lib/IR/LegacyPassManager.cpp:1740:0*
> *#20 0xee3bd2 main
> /home/mtech2/Documents/llvm/llvm/tools/opt/opt.cpp:602:0*
> *#21 0x7f1908700ec5 __libc_start_main
> /build/buildd/eglibc-2.19/csu/libc-start.c:321:0*
> *#22 0xec1739 _start
> (/home/mtech2/Documents/llvm/build/Debug+Asserts/bin/opt+0xec1739)*
> *Stack dump:*
> *0. Program arguments: opt -load
> /home/mtech2/Documents/llvm/build/Debug+Asserts/lib/CSE.so -CSE *
> *1. Running pass 'Function Pass Manager' on module '<stdin>'.*
> *2. Running pass 'Print Instructions' on function '@main'*
> *Aborted (core dumped)*
>
> Any help will be appreciated.
>
>
> - Ansar K.A.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
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