[LLVMdev] how to use "new instruction()"
zhi chen
zchenhn at gmail.com
Fri Apr 17 13:19:39 PDT 2015
Thank you Nick, that's was a stupid error.
On Fri, Apr 17, 2015 at 12:28 PM, Nick Lewycky <nicholas at mxc.ca> wrote:
> zhi chen wrote:
>
>> Thanks Nick, that's something what I am trying to implement as the
>> following. But it seems I still only get the constant value not the
>> instruction. Could you please go over the following instruction and see
>> what wrong with it? Thanks for your time again.
>>
>> Value *vecVal = NULL;
>> IRBuilder<> builder(&*pInst);
>> Type *vecTy = VectorType::get(Type::getDoubleTy(ctxt), 2);
>> Value *emptyVec = UndefValue::get(vecTy);
>> Type* u32Ty = Type::getInt32Ty(currF->getContext());
>> Value *index0 = ConstantInt::get(u32Ty, 0);
>> Value *index1 = ConstantInt::get(u32Ty, 1);
>>
>> Instruction *InsertVal = InsertElementInst::Create(emptyVec, oprnd,
>> index0, "insert");
>>
>
> This makes you:
>
> %insert = insertelement <2 x double> undef, double %oprnd, i32 0
>
> So far so good.
>
> InsertVal = InsertElementInst::Create(emptyVec, oprnd, index1,
>> "insert");
>>
>
> This makes you:
>
> %insert1 = insertelement <2 x double> undef, double %oprnd, i32 1
>
> Not what you wanted. You meant to create:
>
> %insert1 = insertelement <2 x double> %insert, double %oprnd, i32 1
>
> by calling
>
> InsertVal = InsertElementInst::Create(InsertVal, oprnd, index1, "insert");
>
> vecVal = builder.CreateFAdd(emptyVec, emptyVec, "");
>>
>
> This makes you:
>
> %0 = fadd <2 x double> undef, undef
>
> which constant folds away into a non-instruction. You wanted to sum
>
> vecVal = builder.CreateFAdd(InsertVal, [...], "");
>
> where the [...] is because you haven't yet written the code to create the
> second vector (%5) yet.
>
> Nick
>
>
>
>> Best,
>> Zhi
>>
>> On Fri, Apr 17, 2015 at 12:17 PM, Nick Lewycky <nicholas at mxc.ca
>> <mailto:nicholas at mxc.ca>> wrote:
>>
>> zhi chen wrote:
>>
>> I got it. Thanks, Nick. So, it is back to the previous problem.
>> If I
>> have the following instruction:
>>
>> %3 = fadd double %1, double %2
>>
>> I want to change it into
>> %6 = fadd <2 x double> %4, double %5
>>
>> where %4 = <double %1, double %1>, %5 = <double %2, double %2>,
>> how can
>> I do this?
>>
>>
>> %4 = <double %1, double %1> isn't valid syntax, the way you would do
>> it is:
>>
>> %tmp4 = insertelement <2 x double> undef, double %1, i32 0
>> %4 = insertelement <2 x double> %A, double %1, i32 1
>>
>> and similarly for %5, then you create the fadd of the two of them.
>>
>> Nick
>>
>>
>> Thanks,
>> Best
>>
>>
>> On Fri, Apr 17, 2015 at 1:56 AM, Nick Lewycky <nicholas at mxc.ca
>> <mailto:nicholas at mxc.ca>
>> <mailto:nicholas at mxc.ca <mailto:nicholas at mxc.ca>>> wrote:
>>
>> zhi chen wrote:
>>
>> It seems that the problem was because I used
>> builder.CreateFAdd to
>> create a <2 x double> vectortype FADD instruction. It
>> works if I
>> use it
>> to create the scalar version FADD. I want to have an
>> instruction
>> like:
>> *%2 = fadd <2 x double> undef, <2 x double> undef. *The
>> following is the
>> way I used to create the vectorized FADD instruction:
>>
>> //pInst is a double type instruction
>>
>> Type *vecTy = VectorType::get(pInst->getType(), 2);
>> Value *emptyVec = UndefValue::get(vecTy);
>> IRBuilder<> builder(&*pInst);
>> Value *dupVal = builder.CreateFAdd(emptyVec,
>> emptyVec,
>> instName);
>> std::cout << " dupVal " << *dupVal << "\n";
>>
>> It outputs: dupVal <2 x double> <double fadd (double
>> undef, double
>> undef), double fadd (double undef, double undef)>
>>
>> If I dyn_cast the dupVal to instruction type (dupInst)
>> and print
>> dupInst, it outputs: "dupInst printing a <null> value"
>> But if I use Instruction *dupInst = (Instruction *)
>> dupVal and
>> print it,
>> I'll get:
>> dupInst <2 x double> <double fadd (double undef, double
>> undef),
>> double
>> fadd (double undef, double undef)>
>>
>> It seems that if simply fails to generate the
>> vectorized FADD
>> instruction. Anything wrong with my code?
>>
>>
>> IRBuilder gave you back a constant instead of an
>> Instruction. This
>> is why it returns a Value*. For a simple example, if you
>> ask it to
>> create "add i32 1, 2" it will not return an add
>> instruction, it will
>> instead return "i32 3" which is a ConstantInt.
>>
>> In your case, it returned to you a ConstantExpr whose
>> getOpcode()
>> shows Instruction::FAdd, and getOperand(0) and
>> getOperand(1) show
>> 'undef', but it is not an instruction. "Undef" is treated as a
>> constant, so an fadd between two constants gets you a
>> constant
>> instead of an instruction.
>>
>> Usually it won't matter, just build the function top down
>> and don't
>> look at whether you're getting an Instruction* or Constant*
>> and
>> everything will be fine.
>>
>> Nick
>>
>>
>> Best,
>> Zhi
>>
>>
>>
>>
>>
>> On Thu, Apr 16, 2015 at 11:55 PM, zhi chen
>> <zchenhn at gmail.com <mailto:zchenhn at gmail.com>
>> <mailto:zchenhn at gmail.com <mailto:zchenhn at gmail.com>>
>> <mailto:zchenhn at gmail.com <mailto:zchenhn at gmail.com>
>> <mailto:zchenhn at gmail.com <mailto:zchenhn at gmail.com>>>> wrote:
>>
>> Yes. I was using this. It seems the produced
>> instruction is not
>> correct. There are probably some other problems. I
>> need to
>> recheck
>> it. Thanks for your help, Daniel.
>>
>> Best,
>> Zhi
>>
>> On Thu, Apr 16, 2015 at 11:40 PM, Daniel Berlin
>> <dberlin at dberlin.org <mailto:dberlin at dberlin.org>
>> <mailto:dberlin at dberlin.org <mailto:dberlin at dberlin.org>>
>> <mailto:dberlin at dberlin.org <mailto:dberlin at dberlin.org>
>> <mailto:dberlin at dberlin.org <mailto:dberlin at dberlin.org>>>>
>> wrote:
>>
>> Value * is the instruction.
>>
>> use dyn_cast<Instruction> to get to it.
>>
>>
>> On Thu, Apr 16, 2015 at 11:39 PM zhi chen
>> <zchenhn at gmail.com <mailto:zchenhn at gmail.com>
>> <mailto:zchenhn at gmail.com <mailto:zchenhn at gmail.com>>
>> <mailto:zchenhn at gmail.com <mailto:zchenhn at gmail.com>
>> <mailto:zchenhn at gmail.com <mailto:zchenhn at gmail.com>>>> wrote:
>>
>> But IRBuilder.CreateXYZ only returns a
>> "VALUE"
>> type. Can I
>> get the instruction created by it? For
>> example,
>>
>> IRBuilder<> builder(&*pinst);
>> Value *val = builder.CreateFAdd(LV, RV, "");
>>
>> How can I get the fadd instruction created
>> by builder?
>>
>> On Thu, Apr 16, 2015 at 8:52 PM, zhi chen
>> <zchenhn at gmail.com <mailto:zchenhn at gmail.com>
>> <mailto:zchenhn at gmail.com <mailto:zchenhn at gmail.com>>
>> <mailto:zchenhn at gmail.com <mailto:zchenhn at gmail.com>
>> <mailto:zchenhn at gmail.com <mailto:zchenhn at gmail.com>>>> wrote:
>>
>> Yes. That's what I was the solution in
>> my mind.
>> But I
>> just wanted to know if there was a
>> generic way
>> to save
>> some code...
>>
>> On Thu, Apr 16, 2015 at 8:32 PM, Tim
>> Northover
>> <t.p.northover at gmail.com <mailto:t.p.northover at gmail.com>
>> <mailto:t.p.northover at gmail.com <mailto:t.p.northover at gmail.com>>
>> <mailto:t.p.northover at gmail.com <mailto:t.p.northover at gmail.com>
>> <mailto:t.p.northover at gmail.com
>> <mailto:t.p.northover at gmail.com>>>> wrote:
>>
>> > I understand that I can detect the operation
>> first, and use "create" to
>> > create for each of them. But I don't if there is a
>> generic way to do this
>> > because if might be add/sub/mul... operations.
>>
>> I don't think there is.
>> Realistically, just
>> blindly
>> replacing
>> instructions with vector
>> equivalents is
>> only going
>> to work in a few
>> cases anyway. You're probably best
>> to
>> intentionally
>> detect those cases
>> and call the correct CreateXYZ
>> function.
>>
>> Cheers.
>>
>> Tim.
>>
>>
>>
>>
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>>
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>
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