[llvm-dev] Force casting a Value*

[don hinton via llvm-dev]

Sure, you can call store_inst->getOperand(0)->getType(), and call different
functions based on the type, e.g., foo_8, foo_16, foo_32, etc...

Here's an example of how you could do it:
https://github.com/donhinton/CVRFI/blob/master/lib/pass/Node.cpp#L224


On Sun, Jun 11, 2017 at 6:05 PM, Dipanjan Das via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
>
> On 11 June 2017 at 14:04, don hinton <hintonda at gmail.com> wrote:
>
>> Assuming you know it's a 64 bit value, and the function you are calling
>> takes a uint64_t, try this:
>>
>
> The values from the test program are of type: i32/i32*/i32**. Can't I
> interpret these as uint64_t some way?
>
>
>>
>> Value* args[] = {store_inst->getOperand(0)};
>>
>>
>> On Sun, Jun 11, 2017 at 1:16 PM, Dipanjan Das via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>>
>>>
>>> On 11 June 2017 at 12:05, Tim Northover <t.p.northover at gmail.com> wrote:
>>>
>>>> On 11 June 2017 at 11:56, Dipanjan Das via llvm-dev
>>>> <llvm-dev at lists.llvm.org> wrote:
>>>> > I can't pass var_value to a function accepting uint64_t. LLVM
>>>> complains
>>>> > about broken function call.
>>>>
>>>> Well, yes. var_value has type "ConstantInt *", not uint64_t. Assuming
>>>> the value being stored actually is a constant known at compile-time
>>>> you should be able to use cast<ConstantInt *>(vo)->getZExtValue() to
>>>> retrieve a uint64_t value (careful of i128s!).
>>>>
>>>> If that cast fails then you're not dealing with a constant store. This
>>>> is either a nuisance (if you were expecting the possibility and can
>>>> deal with it) or a huge misunderstanding over compile-time vs runtime
>>>> values.
>>>>
>>>
>>> I think it's a misunderstanding in may part. Let me explain my intention
>>> first. I want to retrieve the value (if isPointerTy() returns true) to be
>>> stored by a store instruction at run-time and pass on that value as either
>>> an unsigned int (64) or a pointer (char*) to an external function. The call
>>> to that function is inserted using IRBuilder.CreateCall().
>>>
>>> Consider the code snippet below.
>>>
>>> ==================================================
>>>
>>> if (StoreInst *store_inst = dyn_cast<StoreInst>(&I)) {
>>>                     Value* vo = store_inst->getValueOperand();
>>>                      uint64 var_value = /* cast vo to unsigned int 64
>>> bit */
>>>
>>>                    // Pass on this value to external function
>>>                     IRBuilder<> builder(&I);
>>>                     builder.SetInsertPoint(&B,
>>> ++builder.GetInsertPoint());
>>>                     Constant *func = F.getParent()->getOrInsertFunc
>>> tion("instrument_store",
>>>
>>> Type::getVoidTy(Ctx), Type::getInt8PtrTy(Ctx), NULL);
>>>                     Value* args[] = {var_value};
>>>                     builder.CreateCall(func, args);
>>>  }
>>>
>>> ==================================================
>>>
>>> To reiterate, I want to wrap up the run-time value (var_value) as a
>>> Value* and call the method (instrument_store) with that value as an
>>> argument.
>>>
>>>
>>>
>>>> If it's a nuisance, you can use "dyn_cast" instead of "cast". That'll
>>>> return nullptr if the store wasn't a constant instead of crashing; you
>>>> can decide what to do at that point.
>>>>
>>>> Cheers.
>>>>
>>>> Tim.
>>>>
>>>
>>>
>>>
>>> --
>>>
>>> Thanks & Regards,
>>> Dipanjan
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>
>
>
> --
>
> Thanks & Regards,
> Dipanjan
>
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>
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