[LLVMdev] InsertElementInst and ExtractElementInst

[Vasileios Koutsoumpos]

Hello Tim,

Yes finally it works, the vector was not initialized. Thanks for the help!

Regards,
Vasilis

On 22/07/14 13:36, Tim Northover wrote:
> Hi Vasilis,
>
>> %"ins or1" = insertelement <3 x i32> undef, i32 %38, i32 0
>> %"ins and2" = insertelement <3 x i32> undef, i32 %41, i32 1
>> %"ins xor3" = insertelement <3 x i32> undef, i32 %43, i32 2
>> %extract4 = extractelement <3 x i32> undef, i32 %35
> You're always inserting and extracting with "undef". There's nothing
> linking these operations at all. You actually want them to form a
> chain (so %"ins and2" inserts into the %"ins or1" value, ..., %extrac4
> extracts from "%ins xor3").
>
>> The output of my program is different that the expected one, like the
>> extractelement takes an undefined value.
> It does.
>
>> The instructions I used are:
>> Instruction *Insert0 = InsertElementInst::Create(vector, Or_set, index0,
>> "ins or");
>> ..
>> Instruction *extract = ExtractElementInst::Create(vector, ch, "extract");
>> //where ch takes a value from 0 to 2
>> instr->replaceAllUsesWith(extract); //where I want to replace the instr
>> instruction with the instruction from the vector.
> OK, it looks like you're trying to use the IR in a C-like (non SSA)
> manner. You might want to read around about SSA ("single static
> assignment") form if you haven't already.
>
> In this case, the variable "vector" isn't changed by any of these
> operations, it starts as UNDEF (I assume) and remains UNDEF throughout
> (the instructions don't assign to it). The vector-with-Or_set-inserted
> is "Insert0", so that's what you should use in the next insert, and so
> on.
>
> Cheers.
>
> Tim.