[llvm-dev] Question about 'DAGTypeLegalizer::SplitVecOp_EXTRACT_VECTOR_ELT'

[JinGu via llvm-dev]

Hi Elena,

Thanks for your response.

The store is ok but the extending load generates assertion after the 
store because MemVT is i8 and VT is i1 on following line.

assert(MemVT.getScalarType().bitsLT(VT.getScalarType()) && "Should only 
be an extending load, not truncating!")

so I think we need to use non-extending load for element size less than 
8bit on "DAGTypeLegalizer::SplitVecOp_EXTRACT_VECTOR_ELT" like this roughly.

if 
(N->getOperand(0).getValueType().getVectorElementType().getSizeInBits() 
< 8) {
   return DAG.getLoad(N->getValueType(0), dl, Store, StackPtr, 
MachinePointerInfo());
} else {
    return DAG.getExtLoad(ISD::EXTLOAD, dl, N->getValueType(0), Store, 
StackPtr, MachinePointerInfo(), EltVT);
}

How do you think about it?

Thanks,
JinGu Kang

On 15/09/2017 18:42, Demikhovsky, Elena wrote:
>> extends the elements to 8bit and stores them on stack.
> Store is responsible for zero-extend. This is the policy...
>
> -  Elena
>
>
> -----Original Message-----
> From: jingu at codeplay.com [mailto:jingu at codeplay.com]
> Sent: Friday, September 15, 2017 17:45
> To: llvm-dev at lists.llvm.org; Demikhovsky, Elena <elena.demikhovsky at intel.com>; daniel_l_sanders at apple.com
> Subject: Re: Question about 'DAGTypeLegalizer::SplitVecOp_EXTRACT_VECTOR_ELT'
>
> Can someone give the comment about it please?
>
> Thanks,
>
> JinGu Kang
>
>
> On 14/09/17 12:05, jingu at codeplay.com wrote:
>> Hi All,
>>
>> I have a question about splitting 'EXTRACT_VECTOR_ELT' with 'v2i1'. I
>> have a llvm IR code snippet as following:
>>
>> llvm IR code snippet:
>>
>> for.body:                                         ; preds = %entry,
>> %for.cond
>>    %i.022 = phi i32 [ 0, %entry ], [ %inc, %for.cond ]
>>    %0 = icmp ne <2 x i32> %vecinit1, <i32 0, i32 -23>
>>    %1 = extractelement <2 x i1> %0, i32 %i.022
>>    %vecext4 = extractelement <2 x i32> %vecinit1, i32 %i.022
>>    %vecext5 = extractelement <2 x i32> <i32 0, i32 -23>, i32 %i.022
>>    %cmp6 = icmp ne i32 %vecext4, %vecext5
>>    %cmp7 = xor i1 %1, %cmp6
>>
>> ...
>>
>> and the SelectionDAG before TypeLegalizer is like this.
>>
>>    t0: ch = EntryToken
>>    t2: i32,ch = CopyFromReg t0, Register:i32 %vreg0
>>    t3: ch = ValueType:i32
>>        t5: i32,ch = CopyFromReg t2:1, Register:i32 %vreg1
>>      t7: i32 = AssertZext t5, ValueType:ch:i1
>>    t8: v2i32 = BUILD_VECTOR t2, t7
>>    t11: v2i32 = BUILD_VECTOR Constant:i32<0>, Constant:i32<-23>
>>    t15: i32,ch = CopyFromReg t0, Register:i32 %vreg2
>>            t22: i32 = add t15, Constant:i32<1>
>>          t24: ch = CopyToReg t0, Register:i32 %vreg3, t22
>>          t27: ch = CopyToReg t0, Register:i32 %vreg8, Constant:i32<-1>
>>        t31: ch = TokenFactor t24, t27
>>              t13: v2i1 = setcc t8, t11, setne:ch
>>            t16: i1 = extract_vector_elt t13, t15
>>              t17: i32 = extract_vector_elt t8, t15
>>              t18: i32 = extract_vector_elt t11, t15
>>            t19: i1 = setcc t17, t18, setne:ch
>>          t20: i1 = xor t16, t19
>>
>> ...
>>
>> I have not added any vector register class so 'DAGTypeLegalizer' tries
>> to split the "t16: i1 = extract_vector_elt t13, t15" because  t13's
>> result type is 'v2i1'. If the size of vector element is less than
>> 8bit, 'DAGTypeLegalizer::SplitVecOp_EXTRACT_VECTOR_ELT()' function
>> extends the elements to 8bit and stores them on stack. Finally, the
>> function generates 'ExtLoad' to load specific element. But if the
>> element's size is less than 8bit, I think it could be wrong. It looks
>> it needs just 'Load' or "Load and Truncate" to match the result type
>> of 'EXTRACT_VECTOR_ELT'. How do you think about it? If I missed
>> something, please let me know.
>>
>> Thanks,
>>
>> JinGu Kang
>>
> ---------------------------------------------------------------------
> Intel Israel (74) Limited
>
> This e-mail and any attachments may contain confidential material for
> the sole use of the intended recipient(s). Any review or distribution
> by others is strictly prohibited. If you are not the intended
> recipient, please contact the sender and delete all copies.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20170915/eaf0c51e/attachment.html>