<html><head><base href="x-msg://1126/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi,<div><br></div><div><div><div>I don't think we should make bit casts between pointers with different address spaces illegal. Address spaces are not required to be disjoint. In the N1169 spec, it says </div><div><span style="font-family: Helvetica; "> A non-null pointer into an address space </span><span style="font-family: Helvetica; font-style: oblique; ">A </span><span style="font-family: Helvetica; ">can be cast to a pointer into another address space </span><span style="font-family: Helvetica; font-style: oblique; ">B,
</span><span style="font-family: Helvetica; ">but such a cast is undefined if the source pointer does not point to a location in </span><span style="font-family: Helvetica; font-style: oblique; ">B. </span></div><div><br></div><div>If the address spaces overlap, one should be able to bticast between them. </div><div><br></div><div>-- Mon Ping</div><div><br></div><div><br></div><div>On Sep 7, 2012, at 10:47 AM, Villmow, Micah wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div lang="EN-US" link="blue" vlink="purple"><div class="WordSection1" style="page: WordSection1; "><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">Should LLVM make bitcasts between pointers with different address spaces illegal?<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">This will require a small clarification in the documentation and an assertion check added to the verifier, but I think this would be a good approach.<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">The reason being is that in different address spaces, pointers are not always the same size.<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">This could be limited to make it legal only if the size of the pointer in source and destination address spaces are equivalent, but that seems like more of a work-around than a proper solution.<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">Ideas?<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">Micah<o:p></o:p></div></div>_______________________________________________<br>LLVM Developers mailing list<br><a href="mailto:LLVMdev@cs.uiuc.edu" style="color: blue; text-decoration: underline; ">LLVMdev@cs.uiuc.edu</a><span class="Apple-converted-space"> </span> <a href="http://llvm.cs.uiuc.edu" style="color: blue; text-decoration: underline; ">http://llvm.cs.uiuc.edu</a><br><a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev" style="color: blue; text-decoration: underline; ">http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev</a><br></div></blockquote></div><br></div></body></html>