Resolve {GlobalValue,GloalIndirectSymol}::getBaseObject confusion

While both GlobalAlias and GlobalIFunc are GlobalIndirectSymbol, their
`getIndirectSymbol()` usage is quite different (GlobalIFunc's resolver
is an entity different from GlobalIFunc itself).

As discussed on https://lists.llvm.org/pipermail/llvm-dev/2020-September/144904.html
("[IR] Modelling of GlobalIFunc"), the name `getBaseObject` is confusing when
used with GlobalIFunc.

To resolve the confusion:

* Move GloalIndirectSymol::getBaseObject to GlobalAlias:: (GlobalIFunc should use `getResolver` instead)
* Change GlobalValue::getBaseObject not to inspect GlobalIFunc. Note: the function has 7 references.
* Add GlobalIFunc::getResolverFunction to peel off potential ConstantExpr indirection
  (`strlen` in `test/LTO/Resolution/X86/ifunc.ll`)

Note: GlobalIFunc::getResolver (like GlobalAlias::getAliasee which does not peel
off ConstantExpr indirection) is kept to be used by ValueEnumerator.

Reviewed By: ibookstein

Differential Revision: https://reviews.llvm.org/D109792

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/Object/IRSymtab.cpp b/llvm/lib/Object/IRSymtab.cpp
index 746b008..9208f90 100644
--- a/llvm/lib/Object/IRSymtab.cpp
+++ b/llvm/lib/Object/IRSymtab.cpp
@@ -284,9 +284,13 @@ Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
   }
 
   const GlobalObject *Base = GV->getBaseObject();
-  if (!Base)
-    return make_error<StringError>("Unable to determine comdat of alias!",
-                                   inconvertibleErrorCode());
+  if (!Base) {
+    if (isa<GlobalIFunc>(GV))
+      Base = cast<GlobalIFunc>(GV)->getResolverFunction();
+    if (!Base)
+      return make_error<StringError>("Unable to determine comdat of alias!",
+                                     inconvertibleErrorCode());
+  }
   if (const Comdat *C = Base->getComdat()) {
     Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());
     if (!ComdatIndexOrErr)