Avoid a Symbol -> Name -> Symbol conversion.

Before this we were producing a TargetExternalSymbol from a MCSymbol.
That meant extracting the symbol name and fetching the symbol again
down the pipeline.

This patch adds a DAG.getMCSymbol that lets the MCSymbol pass unchanged on the
DAG.

Doing so removes the need for MO_NOPREFIX and fixes the root cause of pr23900,
allowing r240130 to be committed again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240300 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/ISDOpcodes.h

@@ -124,6 +124,8 @@ namespace ISD {
     TargetExternalSymbol,
     TargetBlockAddress,
 
+    MCSymbol,
+
     /// TargetIndex - Like a constant pool entry, but with completely
     /// target-dependent semantics. Holds target flags, a 32-bit index, and a
     /// 64-bit index. Targets can use this however they like.

include/llvm/CodeGen/MachineOperand.h

@@ -450,11 +450,12 @@ public:
     return Contents.CFIIndex;
   }
 
-  /// getOffset - Return the offset from the symbol in this operand. This always
-  /// returns 0 for ExternalSymbol operands.
+  /// Return the offset from the symbol in this operand. This always returns 0
+  /// for ExternalSymbol operands.
   int64_t getOffset() const {
-    assert((isGlobal() || isSymbol() || isCPI() || isTargetIndex() ||
-            isBlockAddress()) && "Wrong MachineOperand accessor");
+    assert((isGlobal() || isSymbol() || isMCSymbol() || isCPI() ||
+            isTargetIndex() || isBlockAddress()) &&
+           "Wrong MachineOperand accessor");
     return int64_t(uint64_t(Contents.OffsetedInfo.OffsetHi) << 32) |
            SmallContents.OffsetLo;
   }
@@ -512,8 +513,9 @@ public:
   }
 
   void setOffset(int64_t Offset) {
-    assert((isGlobal() || isSymbol() || isCPI() || isTargetIndex() ||
-            isBlockAddress()) && "Wrong MachineOperand accessor");
+    assert((isGlobal() || isSymbol() || isMCSymbol() || isCPI() ||
+            isTargetIndex() || isBlockAddress()) &&
+           "Wrong MachineOperand accessor");
     SmallContents.OffsetLo = unsigned(Offset);
     Contents.OffsetedInfo.OffsetHi = int(Offset >> 32);
   }
@@ -706,6 +708,7 @@ public:
   static MachineOperand CreateMCSymbol(MCSymbol *Sym) {
     MachineOperand Op(MachineOperand::MO_MCSymbol);
     Op.Contents.Sym = Sym;
+    Op.setOffset(0);
     return Op;
   }
 

include/llvm/CodeGen/SelectionDAG.h

@@ -495,6 +495,8 @@ public:
   SDValue getExternalSymbol(const char *Sym, SDLoc dl, EVT VT);
   SDValue getTargetExternalSymbol(const char *Sym, EVT VT,
                                   unsigned char TargetFlags = 0);
+  SDValue getMCSymbol(MCSymbol *Sym, EVT VT);
+
   SDValue getValueType(EVT);
   SDValue getRegister(unsigned Reg, EVT VT);
   SDValue getRegisterMask(const uint32_t *RegMask);
@@ -1278,6 +1280,7 @@ private:
   StringMap<SDNode*> ExternalSymbols;
 
   std::map<std::pair<std::string, unsigned char>,SDNode*> TargetExternalSymbols;
+  DenseMap<MCSymbol *, SDNode *> MCSymbols;
 };
 
 template <> struct GraphTraits<SelectionDAG*> : public GraphTraits<SDNode*> {

include/llvm/CodeGen/SelectionDAGNodes.h

@@ -1810,6 +1810,21 @@ public:
   }
 };
 
+class MCSymbolSDNode : public SDNode {
+  MCSymbol *Symbol;
+
+  friend class SelectionDAG;
+  MCSymbolSDNode(MCSymbol *Symbol, EVT VT)
+      : SDNode(ISD::MCSymbol, 0, DebugLoc(), getSDVTList(VT)), Symbol(Symbol) {}
+
+public:
+  MCSymbol *getMCSymbol() const { return Symbol; }
+
+  static bool classof(const SDNode *N) {
+    return N->getOpcode() == ISD::MCSymbol;
+  }
+};
+
 class CondCodeSDNode : public SDNode {
   ISD::CondCode Condition;
   friend class SelectionDAG;

include/llvm/Target/TargetSelectionDAG.td

@@ -341,6 +341,7 @@ def externalsym : SDNode<"ISD::ExternalSymbol",       SDTPtrLeaf, [],
                          "ExternalSymbolSDNode">;
 def texternalsym: SDNode<"ISD::TargetExternalSymbol", SDTPtrLeaf, [],
                          "ExternalSymbolSDNode">;
+def mcsym: SDNode<"ISD::MCSymbol", SDTPtrLeaf, [], "MCSymbolSDNode">;
 def blockaddress : SDNode<"ISD::BlockAddress",        SDTPtrLeaf, [],
                          "BlockAddressSDNode">;
 def tblockaddress: SDNode<"ISD::TargetBlockAddress",  SDTPtrLeaf, [],