[PATCH] D54925: [NFC] [PowerPC] add an routine in PPCTargetLowering to determine if a global is accessed as toc-indirect or not.

[Qing Shan Zhang via Phabricator via llvm-commits]

steven.zhang created this revision.
steven.zhang added reviewers: sfertile, nemanjai, hfinkel.
Herald added subscribers: jsji, kbarton, hiraditya.

In theory, we should let the PPC target to determine how to lower the TOC Entry for globals. And the PPCTargetLowering require this query to do some optimization for TOC_Entry. I will commit another patch to do that.


https://reviews.llvm.org/D54925

Files:
  llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp
  llvm/lib/Target/PowerPC/PPCISelLowering.h


Index: llvm/lib/Target/PowerPC/PPCISelLowering.h
===================================================================
--- llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -789,6 +789,9 @@
       return true;
     }
 
+    // Returns true if the address of the global is stored in TOC entry.
+    bool isAccessedAsTOCIndirect(SDValue N) const;
+
     bool isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const override;
 
     bool getTgtMemIntrinsic(IntrinsicInfo &Info,
Index: llvm/lib/Target/PowerPC/PPCISelLowering.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -13710,6 +13710,35 @@
   report_fatal_error("Invalid register name global variable");
 }
 
+bool PPCTargetLowering::isAccessedAsTOCIndirect(SDValue GA) const {
+  // 32-bit SVR4 ABI access everything as toc-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 toc-indirect. 
+  if (isa<JumpTableSDNode>(GA) || isa<BlockAddressSDNode>(GA))
+    return true;
+
+  // If the global reference is actually to a non-lazy-pointer, we have to
+  // do an extra load to get the address of the global.
+  if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(GA)) {
+    const GlobalValue *GV = G->getGlobal();
+    unsigned char GVFlags = Subtarget.classifyGlobalReference(GV);
+    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.
Index: llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -4888,9 +4888,9 @@
     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->isAccessedAsTOCIndirect(GA)) {
+      // If it is access as TOC 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);
@@ -4898,18 +4898,7 @@
       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;
-      }
-    }
-
+    // The TOC entry keeps the global address.
     ReplaceNode(N, CurDAG->getMachineNode(PPC::ADDItocL, dl, MVT::i64,
                                           SDValue(Tmp, 0), GA));
     return;


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