[IR] Refactor GlobalIFunc to inherit from GlobalObject, Remove GlobalIndirectSymbol

As discussed in:
* https://reviews.llvm.org/D94166
* https://lists.llvm.org/pipermail/llvm-dev/2020-September/145031.html

The GlobalIndirectSymbol class lost most of its meaning in
https://reviews.llvm.org/D109792, which disambiguated getBaseObject
(now getAliaseeObject) between GlobalIFunc and everything else.
In addition, as long as GlobalIFunc is not a GlobalObject and
getAliaseeObject returns GlobalObjects, a GlobalAlias whose aliasee
is a GlobalIFunc cannot currently be modeled properly. Creating
aliases for GlobalIFuncs does happen in the wild (e.g. glibc). In addition,
calling getAliaseeObject on a GlobalIFunc will currently return nullptr,
which is undesirable because it should return the object itself for
non-aliases.

This patch refactors the GlobalIFunc class to inherit directly from
GlobalObject, and removes GlobalIndirectSymbol (while inlining the
relevant parts into GlobalAlias and GlobalIFunc). This allows for
calling getAliaseeObject() on a GlobalIFunc to return the GlobalIFunc
itself, making getAliaseeObject() more consistent and enabling
alias-to-ifunc to be properly modeled in the IR.

I exercised some judgement in the API clients of GlobalIndirectSymbol:
some were 'monomorphized' for GlobalAlias and GlobalIFunc, and
some remained shared (with the type adapted to become GlobalValue).

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D108872

1 files changed, 14 insertions, 11 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index b3df3a7..349d40e 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -41,7 +41,6 @@
 #include "llvm/IR/GVMaterializer.h"
 #include "llvm/IR/GlobalAlias.h"
 #include "llvm/IR/GlobalIFunc.h"
-#include "llvm/IR/GlobalIndirectSymbol.h"
 #include "llvm/IR/GlobalObject.h"
 #include "llvm/IR/GlobalValue.h"
 #include "llvm/IR/GlobalVariable.h"
@@ -500,7 +499,7 @@ class BitcodeReader : public BitcodeReaderBase, public GVMaterializer {
   SmallVector<Instruction *, 64> InstructionList;
 
   std::vector<std::pair<GlobalVariable *, unsigned>> GlobalInits;
-  std::vector<std::pair<GlobalIndirectSymbol *, unsigned>> IndirectSymbolInits;
+  std::vector<std::pair<GlobalValue *, unsigned>> IndirectSymbolInits;
 
   struct FunctionOperandInfo {
     Function *F;
@@ -2253,8 +2252,7 @@ uint64_t BitcodeReader::decodeSignRotatedValue(uint64_t V) {
 /// Resolve all of the initializers for global values and aliases that we can.
 Error BitcodeReader::resolveGlobalAndIndirectSymbolInits() {
   std::vector<std::pair<GlobalVariable *, unsigned>> GlobalInitWorklist;
-  std::vector<std::pair<GlobalIndirectSymbol *, unsigned>>
-      IndirectSymbolInitWorklist;
+  std::vector<std::pair<GlobalValue *, unsigned>> IndirectSymbolInitWorklist;
   std::vector<FunctionOperandInfo> FunctionOperandWorklist;
 
   GlobalInitWorklist.swap(GlobalInits);
@@ -2283,10 +2281,16 @@ Error BitcodeReader::resolveGlobalAndIndirectSymbolInits() {
       Constant *C = dyn_cast_or_null<Constant>(ValueList[ValID]);
       if (!C)
         return error("Expected a constant");
-      GlobalIndirectSymbol *GIS = IndirectSymbolInitWorklist.back().first;
-      if (isa<GlobalAlias>(GIS) && C->getType() != GIS->getType())
-        return error("Alias and aliasee types don't match");
-      GIS->setIndirectSymbol(C);
+      GlobalValue *GV = IndirectSymbolInitWorklist.back().first;
+      if (auto *GA = dyn_cast<GlobalAlias>(GV)) {
+        if (C->getType() != GV->getType())
+          return error("Alias and aliasee types don't match");
+        GA->setAliasee(C);
+      } else if (auto *GI = dyn_cast<GlobalIFunc>(GV)) {
+        GI->setResolver(C);
+      } else {
+        return error("Expected an alias or an ifunc");
+      }
     }
     IndirectSymbolInitWorklist.pop_back();
   }
@@ -3118,8 +3122,7 @@ Error BitcodeReader::globalCleanup() {
   // Force deallocation of memory for these vectors to favor the client that
   // want lazy deserialization.
   std::vector<std::pair<GlobalVariable *, unsigned>>().swap(GlobalInits);
-  std::vector<std::pair<GlobalIndirectSymbol *, unsigned>>().swap(
-      IndirectSymbolInits);
+  std::vector<std::pair<GlobalValue *, unsigned>>().swap(IndirectSymbolInits);
   return Error::success();
 }
 
@@ -3499,7 +3502,7 @@ Error BitcodeReader::parseGlobalIndirectSymbolRecord(
 
   auto Val = Record[OpNum++];
   auto Linkage = Record[OpNum++];
-  GlobalIndirectSymbol *NewGA;
+  GlobalValue *NewGA;
   if (BitCode == bitc::MODULE_CODE_ALIAS ||
       BitCode == bitc::MODULE_CODE_ALIAS_OLD)
     NewGA = GlobalAlias::create(Ty, AddrSpace, getDecodedLinkage(Linkage), Name,