[LLVMdev] Generating movq2dq using IRBuilder

[Stefanus Du Toit]

On 31-Jul-08, at 2:38 PM, Dan Gohman wrote:
> On Jul 31, 2008, at 7:22 AM, Nicolas Capens wrote:
>> In the same breath I’d also like to kindly ask if someone could have
>> a look at the reverse operations, namely trunk from 128 to 64 bit
>> using movdq2q, and 128 to 32 and 64 to 32 using movd. This also
>> seems related to Bug 2585. Thanks again.
>
> The operations you're describing can be represented as insertelement
> and extractelement in LLVM IR.
>
> I don't know of anyone actively working on MMX tuning for LLVM, so
> if you'd like to see it improve, consider yourself encouraged to
> get involved directly :-).

I noticed that, when doing operations on 64-bit vectors, MMX  
instructions are often emitted even when SSE3 is available. Is this  
really the intent or is it just that SSE versions of certain patterns  
have not been added, and therefore it falls back to MMX versions? It's  
not really encouraged to use MMX (or x87 for that matter) on modern  
microarchitectures if you can get away with SSE.

--
Stefanus Du Toit <stefanus.dutoit at rapidmind.com>
   RapidMind Inc.
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