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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Which options are you seeing that cause the largest difference, and on which targets? As Chandler mentioned there has been a large amount of variation in x86 targets, and there are certain optimizations that can be done, on say a Pentium (scheduling instructions which are pairable and non-dependent so the U and V pipelines are saturated without contention, for example) that don’t make sense to take the time with on a true i386 target. Likewise there were certain optimizations on the i386 such as decomposing multiplications into left shifts which generally wouldn’t be needed on a modern processor. x64 hasn’t seen nearly the same amount of variation since it came into existence. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>-Gordon<o:p></o:p></span></p><p class=MsoNormal><a name="_MailEndCompose"><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></a></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu] <b>On Behalf Of </b>Ghassan Shobaki<br><b>Sent:</b> Sunday, January 15, 2012 2:55 AM<br><b>To:</b> llvmdev@cs.uiuc.edu<br><b>Subject:</b> [LLVMdev] -march and -mtune options on x86<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal style='background:white'><span style='font-family:"Arial","sans-serif";color:black'>I have been doing some benchmarking on x86 using llvm 2.9 with the llvm-gcc 4.2 front end. I noticed that the -march and -mtune options make a significant positive difference in x86-32 mode but hardly make any difference in x86-64 mode. The small difference that I am measuring when the target is x86-64 could easily be random variation, while for the x86-32 target I am measuring a huge difference on some benchmarks. Does anyone have an explanation for this? Does the llvm back end somehow ignore these options when the target is x86-64?<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-family:"Arial","sans-serif";color:black'><o:p> </o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-family:"Arial","sans-serif";color:black'>Thank you in advance!<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-family:"Arial","sans-serif";color:black'>-Ghassan<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-family:"Arial","sans-serif";color:black'><o:p> </o:p></span></p></div></div></div></body></html>