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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal>Hi all,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I am attempting to implement the “reaching definitions” data-flow algorithm on (X86) MachineBasicBlocks for an analysis pass. To do this, I need to compute gen/kill sets for machine basic blocks. To start with, I am only considering the general-purpose registers, RAX-R15 and their sub-registers. Thus, I need to examine each MachineInstr to determine which register(s) it defines and/or uses.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I see in the Doxygen that for a MachineOperand, I can call <span style='font-family:"Courier New"'>isReg()</span> and<span style='font-family:"Courier New"'> getReg()</span> to figure out which X86 register the operand corresponds to. These return an unsigned int “register number”; but I’m not sure how to identify which register actually corresponds to that number.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Also, I will need to identify definitions and uses of registers in instructions. I see that MachineOperand has methods such as <span style='font-family:"Courier New"'>isUse()</span>, <span style='font-family:"Courier New"'>isDef()</span>, and <span style='font-family:"Courier New"'>isKill()</span>, which sound like they might be relevant to what I’m doing; but neither the Doxygen nor the source are particularly helpful as to what they actually do. >From the MachineInstr documentation, I gathered that instructions which define a value are always written so that the value being defined is the first operand; but since X86 has instructions that use more than one register as output (multiplication, for instance), I would need to manually account for the semantics of each instruction. Since X86 has a great many instructions to account for, many of them obscure, I would very much prefer not to go this route if LLVM already provides it! :-)<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>To summarize, my questions are as follows:<o:p></o:p></p><p class=MsoListParagraph style='margin-left:38.25pt;text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>1.<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>How can I determine the actual X86 register that a MachineOperand corresponds to?<o:p></o:p></p><p class=MsoListParagraph style='margin-left:38.25pt;text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>2.<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>What is the best/most straightforward way to determine whether a MachineInstr defines and/or uses a particular register?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks,<o:p></o:p></p><p class=MsoNormal>Ethan Johnson<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><i>Ethan J. Johnson<o:p></o:p></i></p><p class=MsoNormal><i>Computer Science PhD student, Systems group, University of Rochester<o:p></o:p></i></p><p class=MsoNormal><a href="mailto:ejohns48@cs.rochester.edu"><i><span style='color:#0563C1'>ejohns48@cs.rochester.edu</span></i></a><i><o:p></o:p></i></p><p class=MsoNormal><a href="mailto:ethanjohnson@acm.org"><i><span style='color:#0563C1'>ethanjohnson@acm.org</span></i></a><i><o:p></o:p></i></p><p class=MsoNormal><i>PGP pubkey available from public directory or on request<o:p></o:p></i></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>