<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;"><br><div><div>On Jul 9, 2014, at 3:51 PM, Eric Christopher <<a href="mailto:echristo@gmail.com">echristo@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="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;">On Wed, Jul 9, 2014 at 3:12 PM, Evan Cheng <<a href="mailto:evan.cheng@apple.com">evan.cheng@apple.com</a>> wrote:<br><blockquote type="cite"><br><blockquote type="cite">On Jun 17, 2014, at 2:10 PM, Eric Christopher <<a href="mailto:echristo@gmail.com">echristo@gmail.com</a>> wrote:<br><br><blockquote type="cite"><blockquote type="cite">2. Metadata compatibility. We already had precedence of introducing<br>incompatible changes into metadata format in the past within release.<br>Should we use relaxes rules for metadata compatibility?<br></blockquote><br>I think we have a special case for debug metadata (and should document<br>that), but otherwise I think we should hold metadata to the same<br>standard as the rest of the IR.<br><br></blockquote><br>The idea with metadata is that it can be removed and everything still<br>works. I'm definitely not ready to lock down the debug metadata format<br>and I really don't think we should for any of the other uses since<br>stripping already works. (Note, I don't consider function attributes<br>etc as metadata)<br></blockquote><br>We may need to rethink this. If metadata is used only as optimization / codegen hints, then yes I agree they can be dropped. But I suspect there is a need for metadata that’s *required* for correctness. As LLVM continues to gain clients beyond “just” compilers, we will need to be sensitive to their needs. I anticipate use of LLVM bitcode files as persistent object format.<br><br></blockquote><br>I think that metadata that's required for correctness should be baked<br>into the IR and not be metadata - so if there's something we need for<br>correctness we need to come up with an IR extension. See the recent<br>comdat work as an example.<br></div></blockquote></div><br><div>That’s not really a practical suggestion for clients that aren’t essentially clang. The bar to changing the IR is (correctly) very high, essentially unreachable if the client is out-of-tree.</div><div><br></div><div>—Owen</div><div><br></div><div><br></div><div><br></div></body></html>