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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='color:#1F497D'>Ping<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal style='margin-left:36.0pt'><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif";mso-fareast-language:EN-GB'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif";mso-fareast-language:EN-GB'> llvm-commits-bounces@cs.uiuc.edu [mailto:llvm-commits-bounces@cs.uiuc.edu] <b>On Behalf Of </b>Arnaud A. de Grandmaison<br><b>Sent:</b> 12 November 2014 16:58<br><b>To:</b> llvm-commits@cs.uiuc.edu<br><b>Subject:</b> TailRecursionElimination does not cleanup a stale basicblock<o:p></o:p></span></p></div></div><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p><p class=MsoNormal style='margin-left:36.0pt'>When the BasicBlock containing the return instrution has a PHI with 2<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>incoming values, FoldReturnIntoUncondBranch will remove the no longer<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>used incoming value and remove the no longer needed phi as well. This<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>leaves us with a BB that no longer has a PHI, but the subsequent call<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>to FoldReturnIntoUncondBranch from FoldReturnAndProcessPred will not<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>remove the return instruction (which still uses the result of the call<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>instruction). This prevents EliminateRecursiveTailCall to remove<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>the value, as it is still being used in a basicblock which has no<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>predecessors.<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p><p class=MsoNormal style='margin-left:36.0pt'>The basicblock can not be erased on the spot, because its iterator is<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>still being used in runTRE.<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p><p class=MsoNormal style='margin-left:36.0pt'>This issue was exposed when removing the threshold on size for lifetime<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>marker insertion for named temporaries in clang. The testcase is a much<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>reduced version of peelOffOuterExpr(const Expr*, const ExplodedNode *)<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'>from clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp.<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p><p class=MsoNormal style='margin-left:36.0pt'>Cheers,<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'><span style='mso-fareast-language:EN-GB'>--<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='mso-fareast-language:EN-GB'>Arnaud A. de Grandmaison<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p></div></body></html>