<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">On Jan 3, 2014, at 10:17 PM, Andrew Trick <<a href="mailto:atrick@apple.com">atrick@apple.com</a>> wrote:<br><div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div><br></div><blockquote type="cite"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Because the normal case is nomemfence for most address spaces, something else is needed to avoid needing marking every function with nomemfence(0..max address space) when only a few usually matter. I suggest module metadata named !”llvm.used_addrspaces” that will list the address spaces relevant for the module. The absence of a fence will infer nomemfence for all of these address spaces minus any found potential fences. Without the metadata, only nomemfence(0) will be inferred.</div></blockquote><div><br></div><div>Just to be clear, only leaf functions (and functions whose callee graph is contained completely within the module) will be marked.</div><div><br></div><div>Is it possible to indicate an unspecified address space? A nomemfence attribute with no address space would imply no fence in any address space. Would that eliminate the need for metadata?</div></div></blockquote><div><br></div><div>That was my first idea, but I don’t remember why I rejected it originally. I think that would work instead.</div><div><br></div><blockquote type="cite"><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Do you think such an intrinsic would be useful without target support? Do we want a software-only fence?</div></blockquote><br><div>I’m not sure. I don’t think I have much use for it.</div><br><blockquote type="cite"><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div>If you want a hardware fence but want to limit it to the global address space, then maybe the fence instruction should take an address space.</div></div></blockquote><div><br></div>I think the fence instruction should take an address space, but that’s mostly a separate issue. The OpenCL mem_fence/barrier I’m trying to fix isn’t really the same as the fence instruction since it’s for all memory accesses, and not just atomics. I also need at least 6 different target intrinsics with memfences for mem_fence, barrier and all the permutations of address spaces, so a single general memfence intrinsic would be insufficient.<br><div><br></div><blockquote type="cite"><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br><blockquote type="cite"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Does this sound good?</div></blockquote><br></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Overall yes. Thanks.</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">-Andy</div></blockquote></div><br></body></html>