[JITLink][PowerPC] Change method to check if a symbol is external to current object

[lkail]

Summary

After PrePrunePass claimOrExternalizeWeakAndCommonSymbols, a defined symbol might become external. So determine a function call is external or not when building the linkgraph is not accurate. This largely affects updating TOC pointer on PowerPC. TOC pointer is supposed to be the same in one object file(if no mulitple TOC appears) and is updated when control flow transferred to another object file.

This patch defers checking a function call is external or not, in buildTables_ELF_ppc64 which is a PostPrunePass.

This patch fixes failures when jitlink -orc-runtime=/path/to/libort_rt.a is used.

[lkail]

Pre-commit test is in https://github.com/llvm/llvm-project/commit/cee4494c14d821104ad839c44c047bacd652b8dd.

[lhames]

LGTM. Thanks @lkail!

llvm/include/llvm/ExecutionEngine/JITLink/ppc64.h

 class PLTTableManager : public TableManager<PLTTableManager<Endianness>> {
 public:
   PLTTableManager(TOCTableManager<Endianness> &TOC) : TOC(TOC) {}
 
   static StringRef getSectionName() { return "$__STUBS"; }
 
   bool visitEdge(LinkGraph &G, Block *B, Edge &E) {
     Edge::Kind K = E.getKind();
-    if (K == ppc64::RequestPLTCallStubSaveTOC && E.getTarget().isExternal()) {
+    if (K == ppc64::RequestPLTCallStubSaveTOC) {
       E.setKind(ppc64::CallBranchDeltaRestoreTOC);
       this->StubKind = LongBranchSaveR2;
       E.setTarget(this->getEntryForTarget(G, E.getTarget()));
       return true;
     }
-    if (K == ppc64::RequestPLTCallStubNoTOC && E.getTarget().isExternal()) {
+    if (K == ppc64::RequestPLTCallStubNoTOC) {
       E.setKind(ppc64::CallBranchDelta);
       this->StubKind = LongBranchNoTOC;
       E.setTarget(this->getEntryForTarget(G, E.getTarget()));
       return true;
     }
     return false;
   }
 

llvm/lib/ExecutionEngine/JITLink/ELF_ppc64.cpp

Error addSingleRelocation(const typename ELFT::Rela &Rel,
     case ELF::R_PPC64_REL16_LO:
       Kind = ppc64::Delta16LO;
       break;
     case ELF::R_PPC64_REL32:
       Kind = ppc64::Delta32;
       break;
     case ELF::R_PPC64_REL24_NOTOC:
     case ELF::R_PPC64_REL24: {
-      bool isLocal = !GraphSymbol->isExternal();
-      if (isLocal) {
+      bool isExternal =
+          (*ObjSymbol)->isUndefined() && (*ObjSymbol)->isExternal();
+      if (!isExternal) {
         // TODO: There are cases a local function call need a call stub.
         // 1. Caller uses TOC, the callee doesn't, need a r2 save stub.
         // 2. Caller doesn't use TOC, the callee does, need a r12 setup stub.
         // FIXME: For a local call, we might need a thunk if branch target is
         // out of range.
         Kind = ppc64::CallBranchDelta;
         // Branch to local entry.
         Addend += ELF::decodePPC64LocalEntryOffset((*ObjSymbol)->st_other);