From: David Chisnall <csdavec@swan.ac.uk>
Date: Sat, 9 Jan 2010 16:27:31 +0000 (+0000)
Subject: Fixed linking of modules containing aliases to constant bitcasts.  Existing behaviour... 
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=3472246edee4e120e3eb1ec4ad443ba884bc7ac7;p=oota-llvm.git

Fixed linking of modules containing aliases to constant bitcasts.  Existing behaviour first tried to replace the aliases with the global that they aliased (rather than the bitcast), causing a crash on an assert because the types didn't match.  When this was fixed, it then did the same thing creating the new alias (creating an alias with a different type to its aliasee).

Linking modules containing aliases to GEPs is still not quite right.  GEPs that are equivalent to bitcasts will be replaced by bitcasts, GEPs that are not will just break.  Aliases to GEPs that are not equivalent to bitcasts are horribly broken anyway (it might be worth adding an assert when creating the alias to prevent these being created; they just cause problems later).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93052 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Linker/LinkModules.cpp b/lib/Linker/LinkModules.cpp
index d69395cf9b2..dcd696c70d4 100644
--- a/lib/Linker/LinkModules.cpp
+++ b/lib/Linker/LinkModules.cpp
@@ -855,9 +855,14 @@ static bool LinkAlias(Module *Dest, const Module *Src,
     } else {
       // No linking to be performed, simply create an identical version of the
       // alias over in the dest module...
-
+      Constant *Aliasee = DAliasee;
+      // Fixup aliases to bitcasts.  Note that aliases to GEPs are still broken
+      // by this, but aliases to GEPs are broken to a lot of other things, so
+      // it's less important.
+      if (SGA->getType() != DAliasee->getType())
+        Aliasee = ConstantExpr::getBitCast(DAliasee, SGA->getType());
       NewGA = new GlobalAlias(SGA->getType(), SGA->getLinkage(),
-                              SGA->getName(), DAliasee, Dest);
+                              SGA->getName(), Aliasee, Dest);
       CopyGVAttributes(NewGA, SGA);
 
       // Proceed to 'common' steps
@@ -1223,9 +1228,15 @@ static bool LinkAppendingVars(Module *M,
 static bool ResolveAliases(Module *Dest) {
   for (Module::alias_iterator I = Dest->alias_begin(), E = Dest->alias_end();
        I != E; ++I)
-    if (const GlobalValue *GV = I->resolveAliasedGlobal())
-      if (GV != I && !GV->isDeclaration())
-        I->replaceAllUsesWith(const_cast<GlobalValue*>(GV));
+    // We can't sue resolveGlobalAlias here because we need to preserve
+    // bitcasts and GEPs.
+    if (const Constant *C = I->getAliasee()) {
+      while (dyn_cast<GlobalAlias>(C))
+        C = cast<GlobalAlias>(C)->getAliasee();
+      const GlobalValue *GV = dyn_cast<GlobalValue>(C);
+      if (C != I && !(GV && GV->isDeclaration()))
+        I->replaceAllUsesWith(const_cast<Constant*>(C));
+    }
 
   return false;
 }