Hey guys ,
I have question : How to find nearest store to a alloca variable in LLVM ?
I tried to write a LLVM pass for the following C++ program -
#include <stdio.h>
int main()
{
int a ;
int datasize;
datasize = 5;
datasize=10; // most recent definition for the (useless) “datasize=datasize” below.
datasize = datasize;
// Just for verification of result. should be 10.
printf(“value=%d”,a+datasize);
return a+datasize;
}
//==================
I wrote the following LLVM Function Pass for it ( Have not included unecessary details )
for(Function::iterator BB = F.begin() ; BB != F.end() ; ++BB)
{
for(BasicBlock::iterator I = BB->begin(); I != BB->end() ; ++I)
{
if(StoreInst* st = dyn_cast(I))
{
User* user1 = st;
std::string str = user1 ->getOperand(1)->getName();
// it is a store to datasize
if(str=="datasize)
{
Use& use1 = user1->getOperandUse(0) ;
// trying to find nearest assignment/store for this.
Value* v = use1 .get();
errs() << *v << “\n” ;
// this means that it was datasize = datasize
// since it is translated to the following in IR -
// %0 = load i32, i32* %datasize, align 4
// store i32 %0, i32* %datasize, align 4
if(LoadInst* loadInst = dyn_cast(v))
{
User* user2= loadInst ;
Use& use2= user21->getOperandUse(0);
// find nearest defiinion/store
Value* v2 = use2.get();
errs() << “found nearest definiton” << *v2 << “\n” ;
}
}
}
}
}
//===========================================
The result I get -
i32 5 ----------------> ignore,not useful
i32 10 ------------------> ignore,not useful
%0 = load i32, i32* %datasize, align 4
found nearest %datasize = alloca i32, align 4
My Issue : The nearest “def” found for the usage of datasize=datasize is an
alloca instruction while I wanted to find the IR -
store i32 10, i32* %datasize, align 4
(In C++ - "datasize=10" instruction. as seen below).
// … c++ code
datasize = 5;
datasize=10; // most recent definition for the (useless) “datasize=datasize” below.
datasize = datasize;
// … C++ code
Thank you for keeping patience and reading uptil here.
My Question : Can anyone explain how I can find the nearest store to a variable in LLVM IR ?
Thanks,
Malhar