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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple><div class=WordSection1><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'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Chandler Carruth [mailto:chandlerc@google.com] <br><b>Sent:</b> 25 September 2014 11:23<br><b>To:</b> Arnaud De Grandmaison<br><b>Cc:</b> David Blaikie; llvm cfe<br><b>Subject:</b> Re: [PATCH] Emit lifetime start/end for unnamed objects --- take 3<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p><div><div><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p><div><p class=MsoNormal style='margin-left:36.0pt'>On Tue, Sep 16, 2014 at 1:29 AM, Arnaud A. de Grandmaison <<a href="mailto:arnaud.degrandmaison@arm.com" target="_blank">arnaud.degrandmaison@arm.com</a>> wrote:<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>I do not know how this 32 bytes threshold has been choosen, but there is for sure a compile time / stack size gain trade-off to be made.</span><o:p></o:p></p><div><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:36.0pt'>Really? I can't understand why we want *any* threshold here. I think we should aggressively mark all temporaries with this and fix the algorithms to deal with compile time.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:36.0pt'><span style='color:#1F497D'><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'>I will then bootstrap llvm+clang as a testcase, with various thresholds and no threshold so that we know if we have compile time issues or not. We can then decide of the proper follow-up: remove the threshold, or lower it to an acceptable value until some passes get fixed.<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 style='margin-left:36.0pt'> <o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>My experiments have shown that for our customer case, the threshold should be lower: 16-bytes. But changing this threshold would require a separate thread on this list, as well as much more measurements.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>The improvements I have been able to get, by visual inspection of the generated assembly code, for a single call of the hot functions were:</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'> | GCC | Clang | LT-32 | LT-16 |</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>===+=====+=======+=======+=======+</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>F1 | 432 | 608 | 608 | 400 |</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>F2 | 432 | 640 | 640 | 432 |</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>F3 | 384 | 368 | 368 | 192 |</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>F4 | 320 | 400 | 400 | 224 |</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>Stack size is expressed in bytes.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>GCC version 4.8</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>LT-32 is clang with this patch (default 32 bytes threshold for all temporaries).</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:36.0pt'><span style='font-size:11.0pt;font-family:"Courier New";color:#1F497D'>LT-16 is clang with this patch and a 16 bytes threshold for all temporaries.</span><o:p></o:p></p></blockquote></div><div><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p></div><p class=MsoNormal style='mso-margin-top-alt:0cm;margin-right:0cm;margin-bottom:12.0pt;margin-left:36.0pt'>This is, quite simply, amazing. Please push this. Feel free to CC me if you get stuck, this is crazy important to get fixed.<o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'><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'>Thanks Chandler !<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Arnaud<o:p></o:p></span></p><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p></div></div></div></body></html>