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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Thank you for your swift response, Jakob.<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 am not the originator of this patch, but I have been tasked with getting it (or a better version) committed to the LLVM trunk.<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">The original problem came up when trying to run JITed code using 16 byte aligned memory accesses on x86 Android, where, for whatever reason, the stack pointer
was not aligned mod 16 on entry.<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">The “StackAlign” variable in the code seems to indicate the desired stack alignment, rather than the actual stack alignment at runtime. If that is true, then
the expression<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"> MFI->getMaxAlignment() > StackAlign<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">does not actually indicate whether or not the actual stack pointer needs realignment. The proposed patch (changing > to >=) seems to just force realignment
to be done.<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">The test case is run with –realign-stack set to either 0 or 1. If -realign-stack=1 means that the function entry code should cause the stack pointer to be
aligned on entry, then it does so only with the patch.<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">If you can suggest a cleaner way to address this problem, please let me know.<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">Preston<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"><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>
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<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""> Jakob Stoklund Olesen [mailto:stoklund@2pi.dk]
<br>
<b>Sent:</b> Wednesday, January 18, 2012 1:30 PM<br>
<b>To:</b> Gurd, Preston<br>
<b>Cc:</b> llvm-commits@cs.uiuc.edu<br>
<b>Subject:</b> Re: [llvm-commits] [llvm][PATCH][Review Requested] Fix failure to realign stack on x86<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Jan 18, 2012, at 9:55 AM, Gurd, Preston wrote:<o:p></o:p></p>
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<br>
<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">The attached one line patch corrects a problem whereby llvm was failing to generate an ANDL instruction to align the stack pointer on function entry when the required alignment
was mod 16 and when stack realignment was requested.<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="color:black">--- lib/Target/X86/X86RegisterInfo.cpp<span class="apple-tab-span">
</span>(revision 148345)</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="color:black">+++ lib/Target/X86/X86RegisterInfo.cpp<span class="apple-tab-span">
</span>(working copy)</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="color:black">@@ -352,7 +352,7 @@</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="color:black"> const MachineFrameInfo *MFI = MF.getFrameInfo();</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="color:black"> const Function *F = MF.getFunction();</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="color:black"> unsigned StackAlign = TM.getFrameLowering()->getStackAlignment();</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="color:black">- bool requiresRealignment = ((MFI->getMaxAlignment() > StackAlign) ||</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="color:black">+ bool requiresRealignment = ((MFI->getMaxAlignment() >= StackAlign) ||</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="color:black"> F->hasFnAttr(Attribute::StackAlignment));</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I don't understand this change. Why realign the stack when it is already sufficiently aligned?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">/jakob<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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