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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Hi Mehdi,<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 wasn’t familiar with IPRA before, thank you for bringing it up.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">After studying it, I have to say that IPRA is a wonderful idea and is well implemented.<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 tried to reuse the mechanism for the last couple of days.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I implemented a solution using IPRA mechanism and encountered few issues:<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span dir="LTR"></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">IPRA uses immutable analysis pass called “PhysicalRegisterUsageInfo”. The usage of such passes should be optimization only. In
my case, this is a functional issue. The analysis must run in order to be compatible with other compilers.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span dir="LTR"></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">IPRA passes are not enabled by default and when they are enabled many tests fail due to various reasons (mainly because the CallGraph
bottom up approach).<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span dir="LTR"></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">The manipulated RegMasks generated using RegUsageInfoCollector are very different than the manipulated RegMasks that I need.
It will be an abuse to change the current pass implementation. So new pass is required.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><span style="mso-list:Ignore">4.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span dir="LTR"></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">When dumping the MIR after running IPRA passes, assertion is raised because the RegMask name is unknown (same issue that I face
with my solution – see “open Issue”).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I might reuse the analysis pass of IPRA instead of saving the RegMask inside the Machine Function but as mentioned by #1 it is not recommended.<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">Thus I believe that using my current suggestion is more suitable for the issue I am resolving.<o:p></o:p></span></a></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">Best Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Oren<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:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> mehdi.amini@apple.com [mailto:mehdi.amini@apple.com]
<br>
<b>Sent:</b> Monday, January 09, 2017 18:38<br>
<b>To:</b> Ben Simhon, Oren <oren.ben.simhon@intel.com><br>
<b>Cc:</b> llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] RFC: Dynamically Allocated "Callee Saved Registers" Lists<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 9, 2017, at 1:09 AM, Ben Simhon, Oren via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<h1 style="mso-margin-top-alt:12.0pt;margin-right:0cm;margin-bottom:0cm;margin-left:0cm;margin-bottom:.0001pt;line-height:16.95pt;page-break-after:avoid">
<span style="font-size:16.0pt;font-family:"Calibri Light",sans-serif;color:#2E74B5;font-weight:normal">Dynamically Allocated “Callee Saved Registers” Lists<o:p></o:p></span></h1>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Each Calling convention (CC) defines a static list of registers that should be preserved by a callee function. All other registers
should be saved by the caller.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Some CCs use additional condition: If the register is used for passing/returning arguments – the caller needs to save it - even
if it is part of the Callee Saved Registers (CSR) list.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">For example consider the following function:<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;text-indent:36.0pt;line-height:11.65pt">
<i><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">void __regcall func(int a, int b, int c, int d, int e);</span></i><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">According to RegCall CC, parameters<span class="apple-converted-space"> </span><i>d</i><span class="apple-converted-space"> </span>and<span class="apple-converted-space"> </span><i>e</i><span class="apple-converted-space"> </span>should
reside in registers EDI and ESI. The problem is that these registers also appear in the CSR list of RegCall calling convention. So, since the registers were used to pass arguments the callee doesn’t have to preserve their values.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">The current LLVM implementation doesn’t support it. It will save a register if it is part of the static CSR list and will not
care if the register is passed/returned by the callee.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">There are two types of static CSR lists:<span class="apple-converted-space"> </span><o:p></o:p></span></p>
<div style="margin-left:36.0pt">
<p class="MsoNormal" style="text-indent:-18.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">1.</span><span style="font-size:7.0pt"> <span class="apple-converted-space"> </span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">register
mask array of the CSRs (including register aliases)<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:-18.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">2.</span><span style="font-size:7.0pt"> <span class="apple-converted-space"> </span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">register
CSR list<o:p></o:p></span></p>
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<p class="MsoNormal" style="line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">The proposed solution is to dynamically allocate the CSR lists (Only for these CCs). The lists will be updated with actual registers that should
be saved by the callee.<o:p></o:p></span></p>
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<p class="MsoNormal" style="line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Since we need the allocated lists to live as long as the function exists, the list should reside inside the Machine Register Info (MRI) which is
a property of the Machine Function and managed by it (and has the same life span).<o:p></o:p></span></p>
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<p class="MsoNormal" style="line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">The lists should be saved in the MRI and populated upon LowerCall and LowerFormalArguments.<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">Have you looked at how IPRA is implemented? It needs to dynamically allocate the register mask as well, so unless there is something fundamentally different I’m missing, we should share the mechanism.<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">Mehdi<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"><br>
<br>
<o:p></o:p></p>
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<p class="MsoListParagraph" style="mso-margin-top-alt:0cm;margin-right:0cm;margin-bottom:8.0pt;margin-left:0cm;line-height:11.65pt">
<span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<h1 style="mso-margin-top-alt:12.0pt;margin-right:0cm;margin-bottom:0cm;margin-left:0cm;margin-bottom:.0001pt;line-height:16.95pt;page-break-after:avoid">
<span style="font-size:16.0pt;font-family:"Calibri Light",sans-serif;color:#2E74B5;font-weight:normal">Open Issue<o:p></o:p></span></h1>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Machine Instructions (MI) have intermediate representation that can be printed and later on parsed to recreate the MIs.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">MI printer and parser expect the Register Mask array pointer to point to a predefined (static) list of RegMasks. Those lists
are retrieved from auto generated file x86GenRegisterInfo.inc using the functions: getRegMasks() and getRegMaskNames().<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">However, since we create a dynamically allocated register mask, its pointer will not reside in the static lists and no corresponding
name could be found.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">In that case, the MIPrinter will fail to emit the RegMask Name.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">I would appreciate the community opinion regarding my solution and regarding possible solutions to the open issue.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:8.0pt;line-height:11.65pt"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;font-variant-caps: normal;orphans: auto;text-align:start;widows: auto;-webkit-text-stroke-width: 0px;word-spacing:0px">
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