[LLVMdev] Vector code

[Evan Cheng]

llvm does not automatically vectorize your scalar code (as least for  
now). You have to write gcc generic vector code or use vector builtins.

Evan

On May 8, 2008, at 1:46 PM, Nicolas Capens wrote:

> Hi Matthijs,
>
> Yes, I've turned off the link-time optimizations (otherwise it just
> propagates my constant vectors and immediate prints the result). :-)
>
> Here's essentially what I try to generate:
>
> void add(float z[4], float x[4], float y[4])
> {
>   z[0] = x[0] + y[0];
>   z[1] = x[1] + y[1];
>   z[2] = x[2] + y[2];
>   z[3] = x[3] + y[3];
> }
>
> And here's part of the output from the online demo:
>
> LoadInst* float_tmp2 = new LoadInst(ptr_x, "tmp2", false,  
> label_entry);
> LoadInst* float_tmp5 = new LoadInst(ptr_y, "tmp5", false,  
> label_entry);
> BinaryOperator* float_tmp6 = BinaryOperator::create(Instruction::Add,
> float_tmp2, float_tmp5, "tmp6", label_entry);
> StoreInst* void_20 = new StoreInst(float_tmp6, ptr_z, false,  
> label_entry);
> GetElementPtrInst* ptr_tmp10 = new GetElementPtrInst(ptr_x,  
> const_int32_13,
> "tmp10", label_entry);
> LoadInst* float_tmp11 = new LoadInst(ptr_tmp10, "tmp11", false,
> label_entry);
> GetElementPtrInst* ptr_tmp13 = new GetElementPtrInst(ptr_y,  
> const_int32_13,
> "tmp13", label_entry);
> LoadInst* float_tmp14 = new LoadInst(ptr_tmp13, "tmp14", false,
> label_entry);
> BinaryOperator* float_tmp15 = BinaryOperator::create(Instruction::Add,
> float_tmp11, float_tmp14, "tmp15", label_entry);
> ...
>
> So it just processes one element at a time instead of with one (SIMD)
> operation.
>
> Thank you,
>
> -Nicolas (not Anton) :-P
>
>
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev- 
> bounces at cs.uiuc.edu] On
> Behalf Of Matthijs Kooijman
> Sent: Thursday, 08 May, 2008 21:39
> To: LLVM Developers Mailing List
> Subject: Re: [LLVMdev] Vector code
>
> Hi Nicolas (at least, I suspect your signing of your mail with  
> "Anton" was
> not intentional :-p),
>
>> I assume that's the same as the online demo's "Show LLVM C++ API  
>> code"
>> option (http://llvm.org/demo/)? I've tried that with a structure
>> containing four floating-point components but it also appears to add
>> them individually using extract/insert. Maybe I have to try an  
>> array of
> floats...
> Did you turn off the link-time optimization flag (or something like  
> that)?
> If not, the compiler will optimize things like small structs away  
> (though a
> struct of more than 3 elements should not be scalarized directly  
> AFAIK...).
>
> Gr.
>
> Matthijs
>
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