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Hi everyone,</div>
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We have noticed that the SROA pass will only eliminate ‘alloca’ instructions if those are located in the entry basic block of a function.</div>
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<div><i><font face="Calibri,sans-serif"><b>As a general recommendation, should the LLVM IR emitted by our compiler always place ‘alloca’ instructions in the entry basic block ? (I couldn’t find any recommendations concerning this matter.)</b></font></i></div>
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<div><font face="Calibri,sans-serif">In addition, we have noticed that the MemCpy pass will attempt to copy LLVM struct using moves that are as large as possible. </font>For example, a struct of 3 floats is copied using a 64-bit and a 32-bit move. It is therefore
important that such a struct be aligned on 8-byte boundary, not just 4 bytes! Else, one runs the risk of triggering store-forwarding failure pipelining stalls (which we did encountered really badly with one of our internal performance benchmark).</div>
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<div><b><i>Is there any guidelines for specifying the alignment of LLVM structs allocated by alloca instructions ? Is rounding down to the structure size to the next power of 2 a good strategy ? Will the MemCpy pass issue moves of up to 64-bytes on AVX-512
capable processors ?</i></b></div>
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<div>Cheers,</div>
<div>Benoit<i style="font-weight: bold;"> </i></div>
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