[llvm-commits] [llvm] r107613 - /llvm/trunk/lib/Target/X86/README-SSE.txt

[Eli Friedman]

On Mon, Jul 5, 2010 at 6:27 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
> On Sun, Jul 4, 2010 at 10:48 PM, Chris Lattner <sabre at nondot.org> wrote:
>> Author: lattner
>> Date: Mon Jul  5 00:48:41 2010
>> New Revision: 107613
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=107613&view=rev
>> Log:
>> some notes about suboptimal insertps's
>>
>> Modified:
>>    llvm/trunk/lib/Target/X86/README-SSE.txt
>>
>> Modified: llvm/trunk/lib/Target/X86/README-SSE.txt
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README-SSE.txt?rev=107613&r1=107612&r2=107613&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Target/X86/README-SSE.txt (original)
>> +++ llvm/trunk/lib/Target/X86/README-SSE.txt Mon Jul  5 00:48:41 2010
>> @@ -846,3 +846,34 @@
>>  doing a shuffle from v[1] to v[0] then a float store.
>>
>>  //===---------------------------------------------------------------------===//
>> +
>> +On SSE4 machines, we compile this code:
>> +
>> +define <2 x float> @test2(<2 x float> %Q, <2 x float> %R,
>> +       <2 x float> *%P) nounwind {
>> +  %Z = fadd <2 x float> %Q, %R
>> +
>> +  store <2 x float> %Z, <2 x float> *%P
>> +  ret <2 x float> %Z
>> +}
>> +
>> +into:
>> +
>> +_test2:                                 ## @test2
>> +## BB#0:
>> +       insertps        $0, %xmm2, %xmm2
>> +       insertps        $16, %xmm3, %xmm2
>> +       insertps        $0, %xmm0, %xmm3
>> +       insertps        $16, %xmm1, %xmm3
>> +       addps   %xmm2, %xmm3
>> +       movq    %xmm3, (%rdi)
>> +       movaps  %xmm3, %xmm0
>> +       pshufd  $1, %xmm3, %xmm1
>> +                                        ## kill: XMM1<def> XMM1<kill>
>> +       ret
>> +
>> +The insertps's of $0 are pointless complex copies.
>
> I'm also concerned about the pshufd at the end; is the ABI stuff
> really working the way you want it to?

Nevermind; I read this before your email to llvmdev.

-Eli