<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jun 29, 2016 at 9:51 PM, vivek pandya <span dir="ltr"><<a href="mailto:vivekvpandya@gmail.com" target="_blank">vivekvpandya@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr">I have tried out the following code which examines each call site in a module for tail call and do not perform optimization in such case:</div></blockquote><div>bool RegUsageInfoCollector::isEligibleForTailCallOptimization(Function *F) {</div><div> const Module *M = F->getParent();</div><div> for (const Function &Fu : *M)</div><div> for (const BasicBlock &BB : Fu)</div><div> for (const Instruction &II : BB) {</div><div> if (auto CS = ImmutableCallSite(&II))</div><div> if (CS.getCalledFunction() == F && CS.isTailCall()) {</div><div> outs() << "Function : " << F->getName() << " is tailCall\n";</div><div> return true;</div><div> }</div><div> }</div><div> return false;</div><div>}</div><div><br></div><div>This allows many static function from sqlite3 code to be a candidate for local function optimization (that is good compare to previous attempt) but it fails at runtime. I will analyze it but before that I have test-case which fails at -O2 but when I try -O2 -finline-hint-functions it works I am currently analyzing it.</div><div><br></div><div>-Vivek<br></div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div class=""><div class="h5"><div class="gmail_extra"><div class="gmail_quote">On Wed, Jun 29, 2016 at 12:34 AM, Mehdi Amini <span dir="ltr"><<a href="mailto:mehdi.amini@apple.com" target="_blank">mehdi.amini@apple.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word"><span><br><div><blockquote type="cite"><div>On Jun 28, 2016, at 3:01 PM, Matthias Braun <<a href="mailto:matze@braunis.de" target="_blank">matze@braunis.de</a>> wrote:</div><br><div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><blockquote type="cite"><div><br>On Jun 28, 2016, at 11:34 AM, Mehdi Amini via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:</div><br><div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br><br>Sent from my iPhone</div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br>On Jun 28, 2016, at 2:27 PM, Matthias Braun <<a href="mailto:matze@braunis.de" target="_blank">matze@braunis.de</a>> wrote:<br><br></div><blockquote type="cite" style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div><br><div><blockquote type="cite"><div>On Jun 28, 2016, at 10:09 AM, Mehdi Amini via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:</div><br><div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br><br>Sent from my iPhone</div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br>On Jun 28, 2016, at 12:53 PM, vivek pandya <<a href="mailto:vivekvpandya@gmail.com" target="_blank">vivekvpandya@gmail.com</a>> wrote:<br><br></div><blockquote type="cite" style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div><div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jun 28, 2016 at 8:11 PM, Mehdi Amini<span> </span><span dir="ltr"><<a href="mailto:mehdi.amini@apple.com" target="_blank">mehdi.amini@apple.com</a>></span><span> </span>wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word"><br><div><span><blockquote type="cite"><div>On Jun 27, 2016, at 12:25 PM, vivek pandya <<a href="mailto:vivekvpandya@gmail.com" target="_blank">vivekvpandya@gmail.com</a>> wrote:</div><br><div><div dir="ltr">Hello ,<div><br></div><div>To solve this bug locally I have given preference to tail call optimization over local function related optimization in IPRA. I have added following method to achieve this:</div><div><br></div><div><div>bool isEligibleForTailCallOptimization(Function *F) {</div><div> CallingConv::ID CC = F->getCallingConv();</div><div> if (CC == CallingConv::Fast || CC == CallingConv::GHC || CC == CallingConv::HiPE)</div><div> return true;</div><div> return false;</div><div>}</div></div><div><br></div><div>Any other suggestions are always welcomed.</div></div></div></blockquote><div><br></div></span>Why aren’t checking for the presence of a tail call?</div></div></blockquote><div>Are you asking about if tail call optimization is enable or not? If not then above method is inspired from X86ISelLowering::canGuaranteeTCO(). </div><div><br></div></div></div></div></div></blockquote><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br></div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">Are we turning calls into tail calls during codegen?</div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">My assumption is that tail call is inferred on the IR, so you can inspect every *call site*.</div></div></blockquote><div>The final decision on whether to tail call or not is done during instruction selection (it is part of X86TargetLowering::LowerCall()/IsEligibleForTailCallOptimization() for example).</div></div></div></blockquote><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br></div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">Sorry i don't have access to the source code right now, can you clarify if the backend can tail call when the IR didn't mark the call as such, or if what you're referring to is "not honoring the tail call From the IR and demoting to a normal call?</div></div></blockquote><div><br></div></div><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important">The backend does only tail call if the middleend marked the call with the "tail" or "musttail" marker. But that happens for most calls. We can only really transform a franction of those into real tail calls later.</span></div></blockquote><br></div></span><div>Thanks, so back to my original point: if we have to disable the CSR optimization on function that “may be tail called”, it would still be better IMO to do something like `llvm::any_of(callsites, isTailCall)` instead of IsEligibleForTailCallOptimization().</div><div><br></div><div>— </div><span><font color="#888888"><div>Mehdi</div><div><br></div></font></span></div></blockquote></div><br></div>
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