<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div>On Jul 25, 2011, at 10:58 PM, Talin wrote:</div><blockquote type="cite"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex; position: static; z-index: auto; ">To handle the fact that types do not (and can not, at least as long as we intend to support obscure languages like "C" :) have linkage, the the linker uses a "best effort" approach. It attempts to merge types and rewrite IR to use the merged types where it can, but it doesn't make any guarantees.<br>
<font color="#888888"><br></font></blockquote><div>I want to add an additional detail into this mix: That the frontend generating all of this code is making a best effort to insure that the types are in fact compatible -- and it isn't working.</div>
<div><br></div><div>One of the painful things about the old type system was that you were forced to specify every type in excruciating detail - so if I had a type A which had a data member of type B*, I had to include the complete definition of B in my module, even if the module never dereferenced that field - because otherwise my definition of A wouldn't be compatible with another module's definition of A. And if B contained a C* which in turn contained a D*, all of those had to be specified as well, even if the module never used types C or D.</div>
<div><br></div><div>One of the benefits I had hoped to get out of the new system was to be able to "forward declare" a type without giving a definition for it - so if I have my definition of A containing a B*, I only need to declare B as an opaque type instead of giving all the details.</div>
<div><br></div><div>However, it sounds like what you are saying is that if I do this, I can't depend on the linker being able to merge the definition of forward-declared B with fully-specified B, nor A from module 1 (containing forward-declared B*) with A from module 2 (containing fully-specified B*).</div>
<div><br></div><div>If that's true, then it means that we're back to the case where every type has to be fully defined down to the leaf level.</div></div></blockquote><br></div><div>I'm not sure what you mean. LLVM is perfectly fine with opaque structs so long as you don't "deference" them, GEP into them, need their size, etc.</div><div><br></div><div>-Chris</div><br></body></html>