Prevent alias from pointing to weak aliases.

This adds back r204781.

Original message:

Aliases are just another name for a position in a file. As such, the
regular symbol resolutions are not applied. For example, given

define void @my_func() {
  ret void
}
@my_alias = alias weak void ()* @my_func
@my_alias2 = alias void ()* @my_alias

We produce without this patch:

        .weak   my_alias
my_alias = my_func
        .globl  my_alias2
my_alias2 = my_alias

That is, in the resulting ELF file my_alias, my_func and my_alias are
just 3 names pointing to offset 0 of .text. That is *not* the
semantics of IR linking. For example, linking in a

@my_alias = alias void ()* @other_func

would require the strong my_alias to override the weak one and
my_alias2 would end up pointing to other_func.

There is no way to represent that with aliases being just another
name, so the best solution seems to be to just disallow it, converting
a miscompile into an error.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204934 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 12 deletions

diff --git a/include/llvm/IR/GlobalAlias.h b/include/llvm/IR/GlobalAlias.h
index 81777af386..2ca481a515 100644
--- a/include/llvm/IR/GlobalAlias.h
+++ b/include/llvm/IR/GlobalAlias.h
@@ -64,23 +64,15 @@ public:
   Constant *getAliasee() {
     return getOperand(0);
   }
-  /// getAliasedGlobal() - Aliasee can be either global or bitcast of
-  /// global. This method retrives the global for both aliasee flavours.
+
+  /// This method tries to ultimately resolve the alias by going through the
+  /// aliasing chain and trying to find the very last global. Returns NULL if a
+  /// cycle was found.
   GlobalValue *getAliasedGlobal();
   const GlobalValue *getAliasedGlobal() const {
     return const_cast<GlobalAlias *>(this)->getAliasedGlobal();
   }
 
-  /// resolveAliasedGlobal() - This method tries to ultimately resolve the alias
-  /// by going through the aliasing chain and trying to find the very last
-  /// global. Returns NULL if a cycle was found. If stopOnWeak is false, then
-  /// the whole chain aliasing chain is traversed, otherwise - only strong
-  /// aliases.
-  GlobalValue *resolveAliasedGlobal(bool stopOnWeak = true);
-  const GlobalValue *resolveAliasedGlobal(bool stopOnWeak = true) const {
-    return const_cast<GlobalAlias *>(this)->resolveAliasedGlobal(stopOnWeak);
-  }
-
   static bool isValidLinkage(LinkageTypes L) {
     return isExternalLinkage(L) || isLocalLinkage(L) ||
       isWeakLinkage(L) || isLinkOnceLinkage(L);