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Guangming Tan

2011-May-18 07:27 UTC

[LLVMdev] access array problem

于 2011/5/18 14:29, Duncan Sands 写道:> Hi Tan Guangming,
>
>> I want to access an array in my instrumentation code. For example:
>>
>> GlobalVariable:
>> int *counter; //counter the number of load/store operations in run-time
>> int *counterArray; //record the load/store addresses
> strictly speaking these are not arrays, they are pointers.  Also, you have
> written them in some kind of C-style idiom.  What are the declarations in
> LLVM IR?const Type *IntTy = Type::getInt32Ty(M.getContext());
const Type *ATyC = ArrayType::get(Type::getInt64Ty(M.getContext()), 1);

GlobalVariable *CounterSize = new GlobalVariable(M, ATyC, false, 
GlobalValue::InternalLinkage,
Constant::getNullValue(ATyC), "MemTraceCounterSize");

const Type *ATy = ArrayType::get(Type::getInt32Ty(M.getContext()), 3000);
GlobalVariable *Counters = new GlobalVariable(M, ATy, false, 
GlobalValue::InternalLinkage,
Constant::getNullValue(ATy),
"MemTraceCounters");>> //increase the counter if a load/store is performed
>> std::vector<Constant *>index(2);
>> index[0] = Constant::getNullvalue(Type:getInt32Ty(Context));
>> index[1] = Constant::get(Type::getInt32Ty(Context), 0);
> The above two lines both compute the same thing (an i32 constant equal to
> zero) in two different ways.
>
>> Constant *ElementPtr = ConstantExpr::getGetElementPtr(counter,
>> &index[0], index.size());
>> Value *oldcounter = new LoadInst(ElementPtr, "oldcounter",
InsertPos);
>> Value *newcounter = BinaryOperator::Create(Instruction::Add,
>> oldcounter, ConstantInt::get(Type::getInt64Ty(Context), 1),
>> "newcounter", InsertPos);
>> new StoreInst(newcounter, ElmentPtr, InserPos);
>>
>> //store the memory address to counterArray[oldcounter]
>> std::vector<Constant*>   indexC(2);
>> indexC[0] =  Constant::getNullvalue(Type:getInt32Ty(Context));
>> indexC[1] = dync_cast(llvm::ConstantInt>(oldcounter);
> Since oldcounter is not a constant (its value is not known at compile
time...)
> this is never going to work.  Declare the vector to be of Value* not
Constant*.
> Then you don't need the dynamic cast.So, do you mean that we have no way to use the "oldcounter" as an
index
to access an array?>> Constant *ElmentPtr = ConstantExpr::getGetElementPtr(counterArray,
>> &indexC[0], indexC.size());
> This line can then not be a ConstantExpr, it has to be an instruction. 
Again,
> it cannot be a constant since the address computed isn't constant (it
is not
> known at compile time...).
>
> Ciao, Duncan.
>
>> ......// other codes
>>
>> Unfortunately, the oldcounter of Value type can not be cast to
>> ConstantInt, dync_cast returns NULL.
>> Is there any way to retrieve the integer value from oldcounter?
>>
>> Thanks!
>>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

Duncan Sands

2011-May-18 08:04 UTC

head link

[LLVMdev] access array problem

Hi Guangming Tan,
>>> GlobalVariable:
>>> int *counter; //counter the number of load/store operations in
run-time
>>> int *counterArray; //record the load/store addresses
>> strictly speaking these are not arrays, they are pointers.  Also, you
have
>> written them in some kind of C-style idiom.  What are the declarations
in
>> LLVM IR?
> const Type *IntTy = Type::getInt32Ty(M.getContext());
> const Type *ATyC = ArrayType::get(Type::getInt64Ty(M.getContext()), 1);
>
> GlobalVariable *CounterSize = new GlobalVariable(M, ATyC, false,
> GlobalValue::InternalLinkage,
> Constant::getNullValue(ATyC), "MemTraceCounterSize");
so CounterSize is an array of length 1, containing a single 64 bit integer.
Using an array seems rather pointless here.
>
> const Type *ATy = ArrayType::get(Type::getInt32Ty(M.getContext()), 3000);
> GlobalVariable *Counters = new GlobalVariable(M, ATy, false,
> GlobalValue::InternalLinkage,
> Constant::getNullValue(ATy), "MemTraceCounters");
OK, so Counters is an array of 3000 32 bit integers.
>>> Constant *ElementPtr = ConstantExpr::getGetElementPtr(counter,
>>> &index[0], index.size());
What is "counter", the same things as CounterSize?
>>> //store the memory address to counterArray[oldcounter]
>>> std::vector<Constant*>    indexC(2);
>>> indexC[0] =  Constant::getNullvalue(Type:getInt32Ty(Context));
>>> indexC[1] = dync_cast(llvm::ConstantInt>(oldcounter);
>> Since oldcounter is not a constant (its value is not known at compile
time...)
>> this is never going to work.  Declare the vector to be of Value* not
Constant*.
>> Then you don't need the dynamic cast.
> So, do you mean that we have no way to use the "oldcounter" as an
index
> to access an array?
No, this is perfectly possible.  I think you are confusing constants and
instructions.  Instructions are executed at runtime.  Constants are known
at compile time.  You clearly need an instruction here but you are trying
to create a constant.
>>> Constant *ElmentPtr = ConstantExpr::getGetElementPtr(counterArray,
>>> &indexC[0], indexC.size());
Here you should be using GetElementPtrInst::Create to make a getelementptr
instruction rather than using ConstantExpr::getGetElementPtr which creates a
getelementptr constant (which represents a constant address - the address you
are computing is clearly not constant since it changes every time counter is
incremented).

Ciao, Duncan.
>> This line can then not be a ConstantExpr, it has to be an instruction. 
Again,
>> it cannot be a constant since the address computed isn't constant
(it is not
>> known at compile time...).
>>
>> Ciao, Duncan.
>>
>>> ......// other codes
>>>
>>> Unfortunately, the oldcounter of Value type can not be cast to
>>> ConstantInt, dync_cast returns NULL.
>>> Is there any way to retrieve the integer value from oldcounter?
>>>
>>> Thanks!
>>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

Guangming Tan

2011-May-18 08:47 UTC

head link

[LLVMdev] access array problem

Thank you, Duncan.

  I rewrote the code, please help check why it still does not work:

//declare global variable
const Type *IntTy = Type::getInt32Ty(M.getContext());
const Type *ATyC = ArrayType::get(Type::getInt64Ty(M.getContext()), 1);
GlobalVariable *CounterSize = new GlobalVariable(M, ATyC, false, 
GlobalValue::InternalLinkage,
                                                         
Constant::getNullValue(ATyC), "MemTraceCounterSize");

const Type *ATy = ArrayType::get(Type::getInt32Ty(M.getContext()), 3000);
GlobalVariable *Counters = new GlobalVariable(M, ATy, false, 
GlobalValue::InternalLinkage,
                 Constant::getNullValue(ATy), "MemTraceCounters");

//get the index
std::vector<Constant*>IndicesC(2);
IndicesC[0] = Constant::getNullValue(Type::getInt32Ty(Context));
IndicesC[1] = ConstantInt::get(Type::getInt32Ty(Context),0);
Constant *ElementPtrC =  
ConstantExpr::getGetElementPtr(CounterSize,&IndicesC[0],IndicesC.size());
                                                  Value *OldCounterSize 
=new LoadInst(ElementPtrC, "OldCounterSize", InsertPos);
Value *OldCounterSize =new LoadInst(ElementPtrC, "", InsertPos);

//create a getelementptr instruction: we want get &Counters[OldCounterSize]
  std::vector<Value*>new_idx;
new_idx.push_back(OldCounterSize); // ERROR?
Value *nextaddr = GetElementPtrInst::Create(Counters, new_idx.begin(), 
new_idx.end(), "", InsertPos);

Thanks!
? 2011/5/18 16:04, Duncan Sands ??:> Hi Guangming Tan,
>
>>>> GlobalVariable:
>>>> int *counter; //counter the number of load/store operations in
run-time
>>>> int *counterArray; //record the load/store addresses
>>> strictly speaking these are not arrays, they are pointers.  Also,
you have
>>> written them in some kind of C-style idiom.  What are the
declarations in
>>> LLVM IR?
>> const Type *IntTy = Type::getInt32Ty(M.getContext());
>> const Type *ATyC = ArrayType::get(Type::getInt64Ty(M.getContext()), 1);
>>
>> GlobalVariable *CounterSize = new GlobalVariable(M, ATyC, false,
>> GlobalValue::InternalLinkage,
>> Constant::getNullValue(ATyC), "MemTraceCounterSize");
> so CounterSize is an array of length 1, containing a single 64 bit integer.
> Using an array seems rather pointless here.
>
>> const Type *ATy = ArrayType::get(Type::getInt32Ty(M.getContext()),
3000);
>> GlobalVariable *Counters = new GlobalVariable(M, ATy, false,
>> GlobalValue::InternalLinkage,
>> Constant::getNullValue(ATy), "MemTraceCounters");
> OK, so Counters is an array of 3000 32 bit integers.
>
>>>> Constant *ElementPtr = ConstantExpr::getGetElementPtr(counter,
>>>> &index[0], index.size());
> What is "counter", the same things as CounterSize?
>
>>>> //store the memory address to counterArray[oldcounter]
>>>> std::vector<Constant*>     indexC(2);
>>>> indexC[0] =  Constant::getNullvalue(Type:getInt32Ty(Context));
>>>> indexC[1] = dync_cast(llvm::ConstantInt>(oldcounter);
>>> Since oldcounter is not a constant (its value is not known at
compile time...)
>>> this is never going to work.  Declare the vector to be of Value*
not Constant*.
>>> Then you don't need the dynamic cast.
>> So, do you mean that we have no way to use the "oldcounter"
as an index
>> to access an array?
> No, this is perfectly possible.  I think you are confusing constants and
> instructions.  Instructions are executed at runtime.  Constants are known
> at compile time.  You clearly need an instruction here but you are trying
> to create a constant.
>
>>>> Constant *ElmentPtr =
ConstantExpr::getGetElementPtr(counterArray,
>>>> &indexC[0], indexC.size());
> Here you should be using GetElementPtrInst::Create to make a getelementptr
> instruction rather than using ConstantExpr::getGetElementPtr which creates
a
> getelementptr constant (which represents a constant address - the address
you
> are computing is clearly not constant since it changes every time counter
is
> incremented).
>
> Ciao, Duncan.
>
>>> This line can then not be a ConstantExpr, it has to be an
instruction.  Again,
>>> it cannot be a constant since the address computed isn't
constant (it is not
>>> known at compile time...).
>>>
>>> Ciao, Duncan.
>>>
>>>> ......// other codes
>>>>
>>>> Unfortunately, the oldcounter of Value type can not be cast to
>>>> ConstantInt, dync_cast returns NULL.
>>>> Is there any way to retrieve the integer value from oldcounter?
>>>>
>>>> Thanks!
>>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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