<meta http-equiv="Content-Type" content="text/html; charset=utf-8"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div>Hi Krzysztof,</div><div><br></div><div>I have been using RDF on x86 with a lot of success, though I have encountered one weird corner case on several occasions in getLandingPadLiveIns(). I have annotated the code below to highlight the issue:</div><br></div><div dir="ltr">RegisterSet DataFlowGraph::getLandingPadLiveIns() const {<br> RegisterSet LR;<br> const Function &F = MF.getFunction();<br> const Constant *PF = F.hasPersonalityFn() ? F.getPersonalityFn() // PF may be nullptr<br> : nullptr;<br> const TargetLowering &TLI = *MF.getSubtarget().getTargetLowering();<br> if (RegisterId R = TLI.getExceptionPointerRegister(PF))<br> LR.insert(RegisterRef(R));<br> if (RegisterId R = TLI.getExceptionSelectorRegister(PF)) // when PF is nullptr, an assertion fails in the X86 subtarget impl<br> LR.insert(RegisterRef(R));<br> return LR;<br>}</div><div dir="ltr"><br></div><div>The assertion fail then looks like this:</div><div><br></div><div>llvm/lib/Target/X86/X86ISelLowering.cpp:22945: virtual unsigned int llvm::X86TargetLowering::getExceptionSelectorRegister(const llvm::Constant *) const: Assertion `!isFuncletEHPersonality(classifyEHPersonality(PersonalityFn))' failed.</div><div><br></div><div>Could you clarify what the issue may be, and how it might be fixed? (BTW I am using LLVM 8.0.1)</div><div><br></div><div>Thanks,</div><div><br></div><div>Scott Constable</div></div></div></div><br><div class="gmail_quote"><div class="gmail_attr" dir="ltr">On Fri, Jan 10, 2020 at 6:02 AM Krzysztof Parzyszek <<a href="mailto:kparzysz@quicinc.com">kparzysz@quicinc.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid">
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<p class="MsoNormal">Hi Scott,<u></u><u></u></p>
<p class="MsoNormal">Sorry for the late reply, I was out of office during the holidays.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<ol type="1" style="margin-top:0in" start="1">
<li class="gmail-m_-8386465539047594320MsoListParagraph" style="margin-left:0in">A def node can reach either a use node, or another def node. In the highlighted phi node (p3224), the def (d3225) reaches another def (1598) in statement (s1597), that’s why it’s
needed.<u></u><u></u></li><li class="gmail-m_-8386465539047594320MsoListParagraph" style="margin-left:0in">The reason why the def of R11 in s1578 is not connected directly to the use in s1725 is that there may be an intervening def between them (that phi node of the register mask may be
one such def).<u></u><u></u></li></ol>
<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"><span style="font-family:Consolas;font-size:9pt">-- </span>
<span style="font-family:Consolas;font-size:9pt"><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:Consolas;font-size:8pt">Krzysztof Parzyszek
<a href="mailto:kparzysz@quicinc.com" target="_blank"><span style="color:rgb(5,99,193)">kparzysz@quicinc.com</span></a> AI tools development<u></u><u></u></span></p>
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<p class="MsoNormal"><b>From:</b> Scott Douglas Constable <<a href="mailto:sdconsta@syr.edu" target="_blank">sdconsta@syr.edu</a>> <br>
<b>Sent:</b> Friday, December 27, 2019 5:58 PM<br>
<b>To:</b> Krzysztof Parzyszek <<a href="mailto:kparzysz@quicinc.com" target="_blank">kparzysz@quicinc.com</a>><br>
<b>Cc:</b> <a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a><br>
<b>Subject:</b> [EXT] Re: [llvm-dev] Register Dataflow Analysis on X86<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">Hi Krzysztof,<u></u><u></u></p>
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<p class="MsoNormal">Thanks for the reply, I'm starting to understand the graph structure and terminology much better now, especially with the document in RDFGraph.h. I'm still a bit confused about some of the behavior I'm seeing with the phi nodes that involve
aggregate registers. Here is one example:<u></u><u></u></p>
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<p class="MsoNormal"> b1531: --- %bb.36 --- preds(2): %bb.35, %bb.128 succs(1): %bb.37<br>
p3193: phi [+d3194<RBP>(,,u3211):, u3195<RBP>(+d3170,b1526):u1437, u3196<RBP>(d2141,b2486):u2324]<br>
p3197: phi [+d3198<RBX>(,,u3216):, u3199<RBX>(+d3138,b1526):u1465, u3200<RBX>(+d3364,b2486):]<br>
p3201: phi [+d3202<R12D>(,d1541,):, u3203<R12D>(+d3146,b1526):, u3204<R12D>(d1878,b2486):u3148]<br>
p3205: phi [+d3206<#1073741833>(,d1551,u1552):, u3207"<#1073741833>(d1521,b1526):u1524, u3779"<#1073741833>(d1517,b1526):, u3780"<#1073741833>(d1513,b1526):u1522, u3208"<#1073741833>(d2481,b2486):u2484, u3695"<#1073741833>(d2477,b2486):, u3696"<#1073741833>(d2473,b2486):u2482]<br>
s1532: ADJCALLSTACKDOWN64 [d1533<RSP>!(+d3206,\~d3647",u1557):, d1534<EFLAGS>!(+d3206,d1540,):d1533, d1535<SSP>!(+d3206,\~d3646",u1558):d1534, u1536<RSP>!(+d3206):, u1537<SSP>!(+d3206):u1536]<br>
s1538: MOV32r0 [d1539<R12D>(+d3202,,):, d1540<EFLAGS>!(d1534,d1549,):, d1541<R12>(+d3202,,u3221):d1539]<br>
s1542: MOV32ri64 [d1543<RDX>(+d3206,\~d3645",u1561):d1535]<br>
s1544: COPY [d1545<RDI>(+d3206,\~d3644",u1559):d1543, u1546<R13>(d785):]<br>
s1547: MOV32r0 [d1548<ESI>(+d3206,\~d3643",u1560):d1545, d1549<EFLAGS>!(d1540,\~d3642",):]<br>
s1550: MOV64rm [d1551<R11>(+d3206,\~d1554",u1562):d1548, u1552<RIP>(+d3206):u1537]<br>
s1553: CALL64pcrel32 __foo [\~d1554"<#1073741833>!(d1551,d1579,):, \~d3642"<#1073741833>!(d1549,,):, \~d3643"<#1073741833>!(d1548,,):, \~d3644"<#1073741833>!(d1545,,):, \~d3645"<#1073741833>!(d1543,,):, \~d3646"<#1073741833>!(d1535,,):, \~d3647"<#1073741833>!(d1533,,):,
d1555<RSP>!(\~d1554",d1564,u1567):, d1556<SSP>!(\~d1554",d1566,u1568):d1555, u1557<RSP>!(d1533):, u1558<SSP>!(d1535):, u1559<RDI>!(d1545):, u1560<ESI>!(d1548):, u1561<RDX>!(d1543):, u1562<R11>!(d1551):]<br>
s1563: ADJCALLSTACKUP64 [d1564<RSP>!(d1555,,u3778"):, d1565<EFLAGS>!(\~d1554",d1571,):d1556, d1566<SSP>!(d1556,,u3777"):,<u></u><u></u></p>
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<p class="MsoNormal"> u1567<RSP>!(d1555):, u1568<SSP>!(d1556):]<br>
s1569: MOV32r0 [d1570<R10D>(\~d1554",,u3776"):d1565, d1571<EFLAGS>!(d1565,d1574,):]<br>
s1572: MOV32r0 [d1573<R8D>(\~d1554",,u3775"):d1570, d1574<EFLAGS>!(d1571,d1577,):]<br>
s1575: MOV32r0 [d1576<R9D>(\~d1554",,u3774"):d1573, d1577<EFLAGS>!(d1574,,u3773"):]<br>
---> s1578: MOV64rm [d1579<R11>(\~d1554",,u3226"):d1576]<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal" style="margin-bottom:12pt"> b1580: --- %bb.37 --- preds(3): %bb.36, %bb.49, %bb.64 succs(1): %bb.38<br>
p3209: phi [+d3210<RBP>(,d1731,u3212):, u3211<RBP>(+d3194,b1531):, u3212<RBP>(+d3210,b1710):, u3213<RBP>(d1857,b1874):u3466]<br>
p3214: phi [+d3215<RBX>(,,u3217):, u3216<RBX>(+d3198,b1531):, u3217<RBX>(+d3215,b1710):u3257, u3218<RBX>(+d3290,b1874):u3470]<br>
p3219: phi [+d3220<R12D>(,d1712,u1714):, u3221<R12D>(d1541,b1531):, u3222<R12D>(d1712,b1710):u1717, u3223<R12D>(d1878,b1874):u3204]<br>
---> p3224: phi [+d3225<#1073741833>(,d1598,):, u3226"<#1073741833>(d1579,b1531):, u3773"<#1073741833>(d1577,b1531):, u3774"<#1073741833>(d1576,b1531):, u3775"<#1073741833>(d1573,b1531):, u3776"<#1073741833>(d1570,b1531):, u3777"<#1073741833>(d1566,b1531):,
u3778"<#1073741833>(d1564,b1531):, u3227<#1073741833>(d1716,b1710):u1719, u3228"<#1073741833>(d1885,b1874):u3751", u3754"<#1073741833>(d1880,b1874):u1887, u3755"<#1073741833>(d1865,b1874):u3752", u3756"<#1073741833>(d1861,b1874):u3753"]<br>
s1581: IMUL64rri8 [d1582<RAX>(+d3225,d1596,u1592):, d1583<EFLAGS>!(+d3225,d1595,):d1582, u1584<R12>(+d3220):]<br>
s1585: LEA64r [d1586<RSI>(+d3225,,u3772"):d1583, u1587<R15>(d776):, u1588<RAX>(d1582):]<br>
s1589: LEA64r [d1590<RDI>(+d3225,,u3771"):d1586, u1591<R14>(+d3142):u1455, u1592<RAX>(d1582):u1588]<br>
s1593: MOV32r0 [d1594<EAX>(d1582,,):, d1595<EFLAGS>!(d1583,d1599,):, d1596<RAX>(d1582,,u3770"):d1594]<br>
s1597: MOV32r0 [d1598<ECX>(+d3225,,u3769"):d1590, d1599<EFLAGS>!(d1595,,u3231"):]<u></u><u></u></p>
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<p class="MsoNormal">I have used arrows to highlight two nodes. The first node, s1578, def's d1579<R11>, which has a single reached use in phi node p3224. I am surprised that this phi node exists and has no reached uses, for two reasons. First, I built the
graph without the KeepDeadPhis option. Shouldn't this remove phi nodes without reached uses? Second, there clearly
<i>is</i> a reached use of R11 (corresponding to the instruction represented by s1578) in another basic block:<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"> b1721: --- %bb.50 --- preds(1): %bb.49 succs(1): %bb.51<br>
s1722: COPY [d1723<RSI>(+d3248,,u3765"):d1713, u1724<R13>(d785):u1546]<br>
---> s1725: COPY [d1726<RDI>(+d3248,,u3764"):d1723, u1727<R11>(+d3248):]<br>
s1728: MOV32r0 [d1729<EBP>(+d3210,,):, d1730<EFLAGS>!(d1716,,u3261"):, d1731<RBP>(+d3210,,u3253):d1729]<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">I have confirmed via manual inspection and the use of a dynamic analysis tool that the next use of the R11 def in s1578 is s1725.<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">Could you please clarify these two points?<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">Thanks,<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">Scott<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">On Mon, Dec 23, 2019 at 12:46 PM Krzysztof Parzyszek <<a href="mailto:kparzysz@quicinc.com" target="_blank">kparzysz@quicinc.com</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">Hi Scott,<u></u><u></u></p>
<p class="MsoNormal">That #1073741833 is a register mask. They are treated as aggregate registers (essentially sets of registers), so if it includes R9D and R11D, it will be treated as being aliased
with both.<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">These separate defs are there because they reach disjoint registers.<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal"><span style="font-family:Consolas;font-size:9pt">--
</span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-family:Consolas;font-size:8pt">Krzysztof Parzyszek
<a href="mailto:kparzysz@quicinc.com" target="_blank"><span style="color:rgb(5,99,193)">kparzysz@quicinc.com</span></a> AI tools development</span><u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal"><b>From:</b> Scott Douglas Constable <<a href="mailto:sdconsta@syr.edu" target="_blank">sdconsta@syr.edu</a>>
<br>
<b>Sent:</b> Monday, December 23, 2019 2:10 PM<br>
<b>To:</b> Scott Douglas Constable <<a href="mailto:sdconsta@syr.edu" target="_blank">sdconsta@syr.edu</a>><br>
<b>Cc:</b> Krzysztof Parzyszek <<a href="mailto:kparzysz@quicinc.com" target="_blank">kparzysz@quicinc.com</a>>;
<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a><br>
<b>Subject:</b> [EXT] Re: [llvm-dev] Register Dataflow Analysis on X86<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal">Revisiting this thread. I have been experimenting with the RDF module on the X86 target. For the most part, building the data-flow graph and following def-use chains seems to work
fine. But I am also observing some strange behavior in the phi nodes. For example, I have one basic block which begins with the following 4 phi nodes:<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal">b585: --- %bb.25 --- preds(5): %bb.24, %bb.20, %bb.22, %bb.49, %bb.52 succs(2): %bb.18, %bb.37<br>
p1095: phi [+d1096<EBP>(,d668,):, u1097<EBP>(d540,b477):u555, u1098<EBP>(d427,b448):u450, u1099<EBP>(d427,b462):u464, u1100<EBP>(d427,b1009):u1011, u1101<EBP>(d427,b1027):u1029]<br>
p1102: phi [+d1103<R13D>(,,u1075):, u1104<R13D>(d557,b477):u563, u1105<R13D>(d411,b448):, u1106<R13D>(d411,b462):u459, u1107<R13D>(d411,b1009):u1106, u1108<R13D>(d411,b1027):u1107]<br>
p1109: phi [+d1110<R14D>(,d625,u612):, u1111<R14D>(d584,b477):, u1112<R14D>(d452,b448):, u1113<R14D>(d466,b462):, u1114<R14D>(d1013,b1009):, u1115<R14D>(d1031,b1027):]<br>
p1116: phi [+d1117<#1073741833>(,d645,u648):, u1118"<#1073741833>(d579,b477):, u1466"<#1073741833>(d578,b477):, u1467"<#1073741833>(d569,b477):u581, u1468"<#1073741833>(d546,b477):, u1469"<#1073741833>(d543,b477):, u1470"<#1073741833>(d524,b477):u530, u1119"<#1073741833>(d453,b448):,
u1436"<#1073741833>(d420,b448):, u1437"<#1073741833>(d404,b448):u445, u1120"<#1073741833>(d467,b462):, u1438"<#1073741833>(d420,b462):u1436", u1439"<#1073741833>(d404,b462):u473, u1121"<#1073741833>(d1014,b1009):, u1440"<#1073741833>(d420,b1009):u1006, u1441"<#1073741833>(d404,b1009):u1439",
u1122"<#1073741833>(d1032,b1027):, u1442"<#1073741833>(d420,b1027):u1440", u1443"<#1073741833>(d404,b1027):u1441"]<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal">The first three make perfect sense to me, and seem to reflect the post-allocation MIR correctly. The fourth phi node seems entirely composed of defs and uses for some unnamed register
#1073741833 (what exactly is the significance of unnamed registers?). Moreover, this phi seems to be introducing false def-use relationships into the DFG. For example, the phi introduces the following dependency chain, which as far as I can tell is not valid:<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal">// R11D is def'ed, def ID is d524<u></u><u></u></p>
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<p class="MsoNormal">s523: SUB32rr [d524<R11D>(d519,,u1470"):, d525<EFLAGS>!(d520,d533,):, u526<R11D>(d519):, u527<ESI>(d508):]<br>
...<u></u><u></u></p>
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<p class="MsoNormal">// d524 is used in the phi node to def d1117, corresponding to unnamed register #1073741833<br>
p1116: phi [+d1117<#1073741833>(,d645,u648):, u1118"<#1073741833>(d579,b477):, u1466"<#1073741833>(d578,b477):, u1467"<#1073741833>(d569,b477):u581, u1468"<#1073741833>(d546,b477):, u1469"<#1073741833>(d543,b477):, u1470"<#1073741833>(d524,b477):u530, u1119"<#1073741833>(d453,b448):,
u1436"<#1073741833>(d420,b448):, u1437"<#1073741833>(d404,b448):u445, u1120"<#1073741833>(d467,b462):, u1438"<#1073741833>(d420,b462):u1436", u1439"<#1073741833>(d404,b462):u473, u1121"<#1073741833>(d1014,b1009):, u1440"<#1073741833>(d420,b1009):u1006, u1441"<#1073741833>(d404,b1009):u1439",
u1122"<#1073741833>(d1032,b1027):, u1442"<#1073741833>(d420,b1027):u1440", u1443"<#1073741833>(d404,b1027):u1441"]<br>
...<u></u><u></u></p>
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<p class="MsoNormal">// d1117 is used in def d645 of register R9D<br>
s644: ADD32rr [d645<R9D>(+d1117,d694,u659):d634, d646<EFLAGS>!(d633,d651,):, u647<R9D>(+d1117):u637, u648<R9D>(+d1117):u647]<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal">But after examining the corresponding MIR, I do not think that R11D flows into R9D. So it looks to me as though this phi node is erroneous.<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal">Any help wold be much appreciated!<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal">I'm using the LLVM 8.0.1 release.<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal">On Fri, Nov 8, 2019 at 10:35 AM Scott Douglas Constable via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">Do you know whether it has been fixed on the 8.0.1 release?<u></u><u></u></p>
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<p class="MsoNormal">Scott<u></u><u></u></p>
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<p class="MsoNormal">On Fri, Nov 8, 2019 at 9:45 AM Krzysztof Parzyszek <<a href="mailto:kparzysz@quicinc.com" target="_blank">kparzysz@quicinc.com</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">The one blocking issue that existed in the past has been fixed. I haven’t had time to do any work on it lately, but I’m not aware of any fundamental problems that would make it
not work on x86.<u></u><u></u></p>
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<p class="MsoNormal"><span style="font-family:Consolas;font-size:9pt">--
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<p class="MsoNormal"><span style="font-family:Consolas;font-size:8pt">Krzysztof Parzyszek
<a href="mailto:kparzysz@quicinc.com" target="_blank"><span style="color:rgb(5,99,193)">kparzysz@quicinc.com</span></a> AI tools development</span><u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal"><b>From:</b> llvm-dev <<a href="mailto:llvm-dev-bounces@lists.llvm.org" target="_blank">llvm-dev-bounces@lists.llvm.org</a>>
<b>On Behalf Of </b>Scott Douglas Constable via llvm-dev<br>
<b>Sent:</b> Friday, November 8, 2019 10:59 AM<br>
<b>To:</b> <a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a><br>
<b>Subject:</b> [EXT] [llvm-dev] Register Dataflow Analysis on X86<u></u><u></u></p>
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<p class="MsoNormal"><span style="color:rgb(34,34,34);font-family:"Arial",sans-serif;font-size:10pt">I came across this thread from a couple years ago:</span><u></u><u></u></p>
<p class="MsoNormal"><span style="color:rgb(34,34,34);font-family:"Arial",sans-serif;font-size:10pt"> </span><u></u><u></u></p>
<p class="MsoNormal"><span style="color:rgb(34,34,34);font-family:"Arial",sans-serif;font-size:10pt"><a href="http://lists.llvm.org/pipermail/llvm-dev/2017-November/119346.html" target="_blank"><span style="color:rgb(17,85,204)">http://lists.llvm.org/pipermail/llvm-dev/2017-November/119346.html</span></a></span><u></u><u></u></p>
<p class="MsoNormal"><span style="color:rgb(34,34,34);font-family:"Arial",sans-serif;font-size:10pt"> </span><u></u><u></u></p>
<p class="MsoNormal"><span style="color:rgb(34,34,34);font-family:"Arial",sans-serif;font-size:10pt">Has there been any progress on RDF for X86? Or is there some other preferred alternative for performing
reachability analysis after register allocation?</span><u></u><u></u></p>
<p class="MsoNormal"><span style="color:rgb(34,34,34);font-family:"Arial",sans-serif;font-size:10pt"> </span><u></u><u></u></p>
<p class="MsoNormal"><span style="color:rgb(34,34,34);font-family:"Arial",sans-serif;font-size:10pt">Thanks,</span><u></u><u></u></p>
<p class="MsoNormal"><span style="color:rgb(34,34,34);font-family:"Arial",sans-serif;font-size:10pt"> </span><u></u><u></u></p>
<p class="MsoNormal"><span style="color:rgb(34,34,34);font-family:"Arial",sans-serif;font-size:10pt">Scott Constable</span><u></u><u></u></p>
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