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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I would like to understand better the meaning of constant null pointer in LLVM IR.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Can the optimizer assume that dereferencing a null pointer is always unreachable? Or is it only the case for address space 0? Is it ok to have null pointer be a valid pointer for an address space other than 0?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">In InstCombine pass in <span style="font-size:9.5pt;font-family:Consolas">
InstCombiner::visitLoadInst(LoadInst &LI) </span>I see that we replace load of null pointer by unreachable only for address space 0. But there is also code doing the following transformation for all the address spaces:<o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> // load (select (cond, null, P)) -> load P<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> if(isa<ConstantPointerNull>(SI->getOperand(1)) &&
<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> LI.getPointerAddressSpace() == 0) {<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> LI.setOperand(0, SI->getOperand(2));<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> return &LI;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> }<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.5pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal">Is this a bug? Would the correct behavior be to check that the pointers’ address space is 0?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Cheers,<o:p></o:p></p>
<p class="MsoNormal">Thomas<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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