<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jan 9, 2017, at 1:09 AM, Ben Simhon, Oren via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="WordSection1" style="page: WordSection1; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><h1 style="margin: 12pt 0cm 0.0001pt; line-height: 22.61333465576172px; page-break-after: avoid; font-size: 16pt; font-family: 'Calibri Light', sans-serif; color: rgb(46, 116, 181); font-weight: normal;" class="">Dynamically Allocated “Callee Saved Registers” Lists<o:p class=""></o:p></h1><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p class=""> </o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; 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 class=""></o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; 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 class=""></o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;">For example consider the following function:<o:p class=""></o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif; text-indent: 36pt;"><i class="">void __regcall func(int a, int b, int c, int d, int e);<o:p class=""></o:p></i></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;">According to RegCall CC, parameters<span class="Apple-converted-space"> </span><i class="">d</i><span class="Apple-converted-space"> </span>and<span class="Apple-converted-space"> </span><i class="">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 class=""></o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; 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 class=""></o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p class=""> </o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;">There are two types of static CSR lists:<span class="Apple-converted-space"> </span><o:p class=""></o:p></p><div style="margin: 0cm 0cm 0.0001pt 36pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif; text-indent: -18pt;" class=""><span class="">1.<span style="font-style: normal; font-variant-caps: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-family: 'Times New Roman';" class=""> <span class="Apple-converted-space"> </span></span></span><span dir="LTR" class=""></span>register mask array of the CSRs (including register aliases)<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt 36pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif; text-indent: -18pt;" class=""><span class="">2.<span style="font-style: normal; font-variant-caps: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-family: 'Times New Roman';" class=""> <span class="Apple-converted-space"> </span></span></span><span dir="LTR" class=""></span>register CSR list<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt 36pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0cm 0cm 0.0001pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;" class="">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 class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0cm 0cm 0.0001pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;" class="">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 class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0cm 0cm 0.0001pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;" class="">The lists should be saved in the MRI and populated upon LowerCall and LowerFormalArguments.</div></div></div></blockquote><div><br class=""></div><div>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.</div><div><br class=""></div><div>— </div><div>Mehdi</div><div><br class=""></div><div><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div class="WordSection1" style="page: WordSection1; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div style="margin: 0cm 0cm 0.0001pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""></o:p></div><p class="MsoListParagraphCxSpLast" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p class=""> </o:p></p><h1 style="margin: 12pt 0cm 0.0001pt; line-height: 22.61333465576172px; page-break-after: avoid; font-size: 16pt; font-family: 'Calibri Light', sans-serif; color: rgb(46, 116, 181); font-weight: normal;" class="">Open Issue<o:p class=""></o:p></h1><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p class=""> </o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; 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 class=""></o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; 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 class=""></o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; 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 class=""></o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;">In that case, the MIPrinter will fail to emit the RegMask Name.<o:p class=""></o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p class=""> </o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;">I would appreciate the community opinion regarding my solution and regarding possible solutions to the open issue.<o:p class=""></o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 8pt; line-height: 15.546667098999023px; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p class=""> </o:p></p></div><p style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">---------------------------------------------------------------------<br class="">Intel Israel (74) Limited</p><p style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">This e-mail and any attachments may contain confidential material for<br class="">the sole use of the intended recipient(s). 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