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<p class="MsoNormal"><span style="color:#1F497D">I think I have answered my own questions below, but now have additional questions,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I am now using : let Constraints = “$src = $dst”; following examples from X86,
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">rather than TwoOperandAliasConstraint that I had been following from Mips,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">and I am now seeing TIED_TO in my GenInstrInfo.inc for the appropriate OperandInfo’s,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">but I am still seeing assembly code emitted that violates this constraint,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">what else am I missing ?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">thanks, Peter Lawrence.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">the only thing I see that is out-of-the-ordinary in my GenInstrInfo.inc is<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">the OPERAND_MEMORY rather than OPERAND_REGISTER for my base-register operand<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">and OPERAND_MEMORY rather than OPERAND_IMMEDIATE for my offset operand,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">but am still not sure how that happens or what to do to fix it ?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D">static const MCOperandInfo OperandInfo25[] = {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"> { Xmc::AddrRegsRegClassID, 0, MCOI::OPERAND_REGISTER, 0 },<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"> { Xmc::AddrRegsRegClassID, 0, MCOI::OPERAND_MEMORY, ((0 << 16) | (1 << MCOI::TIED_TO)) },<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"> { -1, 0, MCOI::OPERAND_MEMORY, 0 }, };<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I seem to be between a rock and a hard place:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D">let OperandType = "OPERAND_MEMORY" in { <----- I suspect my MEMORY_OPERAND comes from this<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D">def memri : Operand<iPTR> {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"> let MIOperandInfo = (ops addrreg:$base, i16imm:$offset); }<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D">}<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D">def LEA : FMT_I6 <0x4c00, (outs addrreg:$dst), (ins memri:$addr), <----- I suspect the fix would be to split the memri<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"> ----- into separate reg and imm “ins” operands,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"> "lea $dst, ${addr:arith}",<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"> [(set iPTR:$dst, addrri:$addr)]> { <----- but then I would not be able to write this pattern<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"> ----- and ISel would fail ?????<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"> let Constraints = "$addr.base = $dst";<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D"> let isCodeGenOnly = 1;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#1F497D">}<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">-- Sleepless in Silicon Valley...<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Lawerence, Peter
<br>
<b>Sent:</b> Monday, November 23, 2015 3:37 PM<br>
<b>To:</b> 'llvm-dev@lists.llvm.org'<br>
<b>Subject:</b> Qs about TwoOperandAliasConstraint and TIED_TO<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">in llvm-3.6.2.src<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">1. when I put this around one of my instruction definitions in my target “InstrInfo.td” file,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">let TwoOperandAliasConstraint = "$dst = $rs1" in {<o:p></o:p></p>
<p class="MsoNormal">}<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I do not see any TIED_TO in the generated GenInstrInfo.inc file for the OperandInfo used by the instruction,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">the question is what am I doing wrong ?<o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> you are doing nothing wrong, the same thing happens for Mips,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> all its’ ArithLogicR and ArithLogicI instructions have let TwoOperandAliasConstraint = “$rd = $rs”;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> but if you look at MipsGenInstrInfo.inc<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> AND, OR, XOR, ADD, SUB, ADDu, SUBu, etc..., use OperandInfo14 does not contain any TIED_TO<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> ANDi, ORi, XORi, ADDi, SUBi, ADDui, SUBui, etc..., use OperandInfo29 does not contain any TIED_TO<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> there is probably a bug somewhere in utils/TableGen/<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> this is probably working for Mips in the case of ArithLogicR, since those instructions really are 3-operand<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> but it is mysterious how RA gets it right for the ArithLogicI case, since those instructions really are 2-operand<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> IMHO, from a Software Engineering point of view TwoOperandAliasConstraint should either be fixed or deleted,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> currently it is misleading, and in a target-description that should be usable as a reference design<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> (as Mips can be viewed as the quintessential RISC instruction set), at least I tried to use it as such.<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">2. I’ve noticed that TwoOperandAliasConstraint does not appear anywhere in source/lib/Target/X86/*<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">yet TIED_TO occurs in 162 of the OperandInfo’s in build/lib/Target/X86/X86GenInstrInfo.inc<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">the question is how does TIED_TO happen if not by TwoOperandAliasConstraint ?<o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> searching X86InstrInfo.td and X86GenInstrInfo.inc it is seems that<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> let Constraints = “$src = $dst”;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">---> gets recognized by TableGen and converted into a TIED_TO constraint<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">thanks, Peter Lawrence.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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