[AIX][XCOFF] Generate undefined symbol in symbol table for external function call

Summary:
This patch sets up the infrastructure for

 1. Associate MCSymbolXCOFF with an MCSectionXCOFF when it could not
    get implicitly associated.
 2. Generate undefined symbols. The patch itself generates undefined symbol
    for external function call only. Generate undefined symbol for external
    global variable and external function descriptors will be handled in
    separate patch(s) after this is land.

Differential Revision: https://reviews.llvm.org/D70443

1 files changed, 14 insertions, 2 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 4d9288ce798..ff704b7299a 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -5325,8 +5325,20 @@ SDValue PPCTargetLowering::FinishCall(
     // C-linkage name.
     GlobalAddressSDNode *G = cast<GlobalAddressSDNode>(Callee);
     auto &Context = DAG.getMachineFunction().getMMI().getContext();
-    MCSymbol *S = Context.getOrCreateSymbol(Twine(".") +
-                                            Twine(G->getGlobal()->getName()));
+
+    MCSymbolXCOFF *S = cast<MCSymbolXCOFF>(Context.getOrCreateSymbol(
+        Twine(".") + Twine(G->getGlobal()->getName())));
+
+    const GlobalValue *GV = G->getGlobal();
+    if (GV && GV->isDeclaration() && !S->hasContainingCsect()) {
+      // On AIX, undefined symbol need to associate with a MCSectionXCOFF to
+      // get the correct storage mapping class. In this case, XCOFF::XMC_PR.
+      MCSectionXCOFF *Sec =
+          Context.getXCOFFSection(S->getName(), XCOFF::XMC_PR, XCOFF::XTY_ER,
+                                  XCOFF::C_EXT, SectionKind::getMetadata());
+      S->setContainingCsect(Sec);
+    }
+
     Callee = DAG.getMCSymbol(S, PtrVT);
     // Replace the GlobalAddressSDNode Callee with the MCSymbolSDNode.
     Ops[1] = Callee;