[NFC] [PowerPC] add an routine in PPCTargetLowering to determine if a global is accessed as got-indirect or not.

In theory, we should let the PPC target to determine how to lower the TOC Entry for globals. 
And the PPCTargetLowering requires this query to do some optimization for TOC_Entry. 

Differential Revision: https://reviews.llvm.org/D54925

llvm-svn: 348108

lib/Target/PowerPC/PPCISelDAGToDAG.cpp

@@ -4897,9 +4897,9 @@ void PPCDAGToDAGISel::Select(SDNode *N) {
     SDValue TOCbase = N->getOperand(1);
     SDNode *Tmp = CurDAG->getMachineNode(PPC::ADDIStocHA, dl, MVT::i64,
                                          TOCbase, GA);
-
-    if (isa<JumpTableSDNode>(GA) || isa<BlockAddressSDNode>(GA) ||
-        CModel == CodeModel::Large) {
+    if (PPCLowering->isAccessedAsGotIndirect(GA)) {
+      // If it is access as got-indirect, we need an extra LD to load
+      // the address.
       SDNode *MN = CurDAG->getMachineNode(PPC::LDtocL, dl, MVT::i64, GA,
                                           SDValue(Tmp, 0));
       transferMemOperands(N, MN);
@@ -4907,18 +4907,7 @@ void PPCDAGToDAGISel::Select(SDNode *N) {
       return;
     }
 
-    if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(GA)) {
-      const GlobalValue *GV = G->getGlobal();
-      unsigned char GVFlags = PPCSubTarget->classifyGlobalReference(GV);
-      if (GVFlags & PPCII::MO_NLP_FLAG) {
-        SDNode *MN = CurDAG->getMachineNode(PPC::LDtocL, dl, MVT::i64, GA,
-                                            SDValue(Tmp, 0));
-        transferMemOperands(N, MN);
-        ReplaceNode(N, MN);
-        return;
-      }
-    }
-
+    // Build the address relative to the TOC-pointer..
     ReplaceNode(N, CurDAG->getMachineNode(PPC::ADDItocL, dl, MVT::i64,
                                           SDValue(Tmp, 0), GA));
     return;

lib/Target/PowerPC/PPCISelLowering.cpp

@@ -13710,6 +13710,35 @@ unsigned PPCTargetLowering::getRegisterByName(const char* RegName, EVT VT,
   report_fatal_error("Invalid register name global variable");
 }
 
+bool PPCTargetLowering::isAccessedAsGotIndirect(SDValue GA) const {
+  // 32-bit SVR4 ABI access everything as got-indirect.
+  if (Subtarget.isSVR4ABI() && !Subtarget.isPPC64())
+    return true;
+
+  CodeModel::Model CModel = getTargetMachine().getCodeModel();
+  // If it is small or large code model, module locals are accessed
+  // indirectly by loading their address from .toc/.got. The difference
+  // is that for large code model we have ADDISTocHa + LDtocL and for
+  // small code model we simply have LDtoc.
+  if (CModel == CodeModel::Small || CModel == CodeModel::Large)
+    return true;
+
+  // JumpTable and BlockAddress are accessed as got-indirect. 
+  if (isa<JumpTableSDNode>(GA) || isa<BlockAddressSDNode>(GA))
+    return true;
+
+  if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(GA)) {
+    const GlobalValue *GV = G->getGlobal();
+    unsigned char GVFlags = Subtarget.classifyGlobalReference(GV);
+    // The NLP flag indicates that a global access has to use an
+    // extra indirection.
+    if (GVFlags & PPCII::MO_NLP_FLAG)
+      return true;
+  }
+
+  return false;
+}
+
 bool
 PPCTargetLowering::isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const {
   // The PowerPC target isn't yet aware of offsets.

lib/Target/PowerPC/PPCISelLowering.h

@@ -789,6 +789,9 @@ namespace llvm {
       return true;
     }
 
+    // Returns true if the address of the global is stored in TOC entry.
+    bool isAccessedAsGotIndirect(SDValue N) const;
+
     bool isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const override;
 
     bool getTgtMemIntrinsic(IntrinsicInfo &Info,