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<p class="MsoNormal"><span style="color:black">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">We have implemented the rcp instruction generation for X86 target architecture. We have introduced a flag -fp-rcp flag which controls the generatation of X86 rcp instruction generation.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">We have observed minor effects on precision and hence hve put these transformations under the mentioned flag.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">Note that –fp-rcp is only enabled with -enable-unsafe-fp-math flag presently.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">Moreover we have achieved some derived optimizations along with rsqrt generations.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">Following is the details of the -fp-rcp flag along with its values and enabled optimizations.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black"> -fp-rcp <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> =off - No rcp<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> =on - y/x => y * rcp(x) // Standard<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> =fda - Standard, Derive FMA i.e. y/x +z => y * rcp(x) + z => vfmaddss y rcp(x) z.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> This is termed as FDA(Fused Division Accumulate)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">Sending the code patch(on llvm svn revision 167927), text description and testcases attached with this mail. Please review.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">Future enhance plans are as follows.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">TODO: <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">1. Enable vector rsqrt generation.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">2. Generate different variations of FDA i.e. FMSUB, FNMSUB,FNMADD instruction generations as required.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">Best Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">soham<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b><i><span style="font-family:"Bookman Old Style","serif";color:#BFBFBF">"The search for truth is more precious than its possession."<o:p></o:p></span></i></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
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