<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Jul 15, 2019, at 14:34, Cashman, David via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Given a ptrtoint followed by inttoptr:<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><b class="">%tmp = ptrtoint i16 addrspace(4)* %a to i32<o:p class=""></o:p></b></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><b class="">%b = inttoptr i32 %tmp to i8*<o:p class=""></o:p></b></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">InstCombine will normally collapse them to a bitcast (or no-op, if the src and dst pointer types are the same). But if the pointers are in different address spaces, as shown above, it won’t, due to the following code in Instructions.cpp:<br class=""><br class=""><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: "Courier New";" class=""> // Cannot simplify if address spaces are different!<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: "Courier New";" class=""> if (SrcTy->getPointerAddressSpace() != DstTy->getPointerAddressSpace())<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: "Courier New";" class=""> return 0;<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Is this correct? Given that the instructions above are effectively casting the pointer between two address spaces, can/should InstCombine replace the code above with an addrspacecast? Is there something in the LLVM language spec that makes it illegal or undesirable?<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Thanks,<br class=""><br class="">David<o:p class=""></o:p></div></div><br class=""></div></blockquote><div><br class=""></div>This would be illegal. This is something resembling a no-op addrspacecast, and would only be valid if the target defined representations of both address spaces is known identical. Addrspacecast can change the representation of the pointer in complex ways which would not happen with the ptrtoint/inttoptr pair.</div><div><br class=""></div><div>-Matt</div></body></html>