[PATCH] sectiongroup support

[kledzik at apple.com]

================
Comment at: lib/Core/SymbolTable.cpp:61
@@ +60,3 @@
+        if (r->kindValue() == Reference::kindGroupParent) {
+          addGroupChild(atom, *(r->target()));
+          return;
----------------
Shankar Kalpathi Easwaran wrote:
> kledzik at apple.com wrote:
> > Shankar Kalpathi Easwaran wrote:
> > > Rui Ueyama wrote:
> > > > *r->target()
> > > ok.
> > Why is addGroupChild() called here, and what does it do? Scanning all references of all atoms will slow things down.
> > 
> > Instead, inside addGroup(), if the group name already exists, you choose one of the groups to use (first one?), then mark it to be replaced.   Later in Resolver::removeCoalescedAwayAtoms() you can find the child of coalesced away groups.
> a) To catch a bug / error in the YAML file / reader that the user forgot to include a group child atom in the group atom.
> b) When the groupChild atoms appear before the groupComdat atoms.
> 
> Do we want to track the groupChild atoms as normal atoms ? If so how do we identify an error that the atom was not included inside a group ?
> 
YAML errors should be checked by the YAML Reader.  No need to slow down the core linker.

I don't see the issue if a child is added to the symbol table before the group is added.  It will just be a regular atom. Later if the group is replaced, the child will be marked replaced too.  

Any sort of checking for malformed groups should be done in the readers (YAML and ELF).  



http://llvm-reviews.chandlerc.com/D2961