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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve been surprised by how “over the top” the set of opts in DAGCombiner are,<o:p></o:p></p>
<p class="MsoNormal">But here’s one that might be missing<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Array[ I + (pointer-difference) ]<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Generates ... (shl (sra (sub pointer1, pointer2), 2), 2) ...<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Which gets Combined into<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> (and (sub pointer1, pointer2), -4)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">But IIUC the C/C++ languages require pointer1 and pointer2 to be addresses of elements in the same array,<o:p></o:p></p>
<p class="MsoNormal">So their difference must be (0 mod element-size),<o:p></o:p></p>
<p class="MsoNormal">(even if the array itself is somehow misaligned, the difference between elements will be aligned)<o:p></o:p></p>
<p class="MsoNormal">so the “SRA” is only shifting out zeros,<o:p></o:p></p>
<p class="MsoNormal">So the “AND” by “-4” is superfluous<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Please let me know if I am misunderstanding something ?!<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">--Peter Lawrence.<o:p></o:p></p>
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