Restore some "small section" support code, reverting my patch from r76936.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78894 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Mips/MipsISelLowering.cpp

@@ -210,6 +210,37 @@ AddLiveIn(MachineFunction &MF, unsigned PReg, TargetRegisterClass *RC)
   return VReg;
 }
 
+// A address must be loaded from a small section if its size is less than the 
+// small section size threshold. Data in this section must be addressed using 
+// gp_rel operator.
+bool MipsTargetLowering::IsInSmallSection(unsigned Size) {
+  return (Size > 0 && (Size <= Subtarget->getSSectionThreshold()));
+}
+
+// Discover if this global address can be placed into small data/bss section. 
+bool MipsTargetLowering::IsGlobalInSmallSection(GlobalValue *GV)
+{
+  const TargetData *TD = getTargetData();
+  const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
+
+  if (!GVA)
+    return false;
+  
+  const Type *Ty = GV->getType()->getElementType();
+  unsigned Size = TD->getTypeAllocSize(Ty);
+
+  // if this is a internal constant string, there is a special
+  // section for it, but not in small data/bss.
+  if (GVA->hasInitializer() && GV->hasLocalLinkage()) {
+    Constant *C = GVA->getInitializer();
+    const ConstantArray *CVA = dyn_cast<ConstantArray>(C);
+    if (CVA && CVA->isCString()) 
+      return false;
+  }
+
+  return IsInSmallSection(Size);
+}
+
 // Get fp branch code (not opcode) from condition code.
 static Mips::FPBranchCode GetFPBranchCodeFromCond(Mips::CondCode CC) {
   if (CC >= Mips::FCOND_F && CC <= Mips::FCOND_NGT)
@@ -485,17 +516,23 @@ LowerSELECT(SDValue Op, SelectionDAG &DAG)
                      Cond, True, False, CCNode);
 }
 
-SDValue MipsTargetLowering::
+SDValue MipsTargetLowering::LowerGlobalAddress(SDValue Op, SelectionDAG &DAG) {
-LowerGlobalAddress(SDValue Op, SelectionDAG &DAG) 
-{
   // FIXME there isn't actually debug info here
   DebugLoc dl = Op.getDebugLoc();
   GlobalValue *GV = cast<GlobalAddressSDNode>(Op)->getGlobal();
   SDValue GA = DAG.getTargetGlobalAddress(GV, MVT::i32);
 
   if (getTargetMachine().getRelocationModel() != Reloc::PIC_) {
+    SDVTList VTs = DAG.getVTList(MVT::i32);
+    
+    // %gp_rel relocation
+    if (!isa<Function>(GV) && IsGlobalInSmallSection(GV)) { 
+      SDValue GPRelNode = DAG.getNode(MipsISD::GPRel, dl, VTs, &GA, 1);
+      SDValue GOT = DAG.getGLOBAL_OFFSET_TABLE(MVT::i32);
+      return DAG.getNode(ISD::ADD, dl, MVT::i32, GOT, GPRelNode); 
+    }
     // %hi/%lo relocation
-    SDValue HiPart = DAG.getNode(MipsISD::Hi, dl, MVT::i32, GA);
+    SDValue HiPart = DAG.getNode(MipsISD::Hi, dl, VTs, &GA, 1);
     SDValue Lo = DAG.getNode(MipsISD::Lo, dl, MVT::i32, GA);
     return DAG.getNode(ISD::ADD, dl, MVT::i32, HiPart, Lo);
 

lib/Target/Mips/MipsISelLowering.h

@@ -66,8 +66,8 @@ namespace llvm {
   //===--------------------------------------------------------------------===//
   // TargetLowering Implementation
   //===--------------------------------------------------------------------===//
-  class MipsTargetLowering : public TargetLowering 
+  
-  {
+  class MipsTargetLowering : public TargetLowering  {
   public:
 
     explicit MipsTargetLowering(MipsTargetMachine &TM);
@@ -88,6 +88,9 @@ namespace llvm {
     // Subtarget Info
     const MipsSubtarget *Subtarget;
 
+    bool IsGlobalInSmallSection(GlobalValue *GV); 
+    bool IsInSmallSection(unsigned Size); 
+
     // Lower Operand helpers
     SDValue LowerCallResult(SDValue Chain, SDValue InFlag,
                             unsigned CallConv, bool isVarArg,

lib/Target/Mips/MipsSubtarget.cpp

@@ -17,6 +17,11 @@
 #include "llvm/Support/CommandLine.h"
 using namespace llvm;
 
+static cl::opt<unsigned>
+SSThreshold("mips-ssection-threshold", cl::Hidden,
+            cl::desc("Small data and bss section threshold size (default=8)"),
+            cl::init(8));
+
 MipsSubtarget::MipsSubtarget(const std::string &TT, const std::string &FS,
                              bool little) : 
   MipsArchVersion(Mips1), MipsABI(O32), IsLittle(little), IsSingleFloat(false),
@@ -30,6 +35,9 @@ MipsSubtarget::MipsSubtarget(const std::string &TT, const std::string &FS,
   // Parse features string.
   ParseSubtargetFeatures(FS, CPU);
 
+  // Small section size threshold
+  SSectionThreshold = SSThreshold;
+
   // Is the target system Linux ?
   if (TT.find("linux") == std::string::npos)
     IsLinux = false;

lib/Target/Mips/MipsSubtarget.h

@@ -60,6 +60,10 @@ protected:
   // isLinux - Target system is Linux. Is false we consider ELFOS for now.
   bool IsLinux;
 
+  // Put global and static items less than or equal to SSectionThreshold 
+  // bytes into the small data or bss section. The default is 8.
+  unsigned SSectionThreshold;
+
   /// Features related to the presence of specific instructions.
   
   // HasSEInReg - SEB and SEH (signext in register) instructions.
@@ -109,6 +113,7 @@ public:
   bool isNotSingleFloat() const { return !IsSingleFloat; };
   bool hasVFPU() const { return HasVFPU; };
   bool isLinux() const { return IsLinux; };
+  unsigned getSSectionThreshold() const { return SSectionThreshold; }
 
   /// Features related to the presence of specific instructions.
   bool hasSEInReg()   const { return HasSEInReg; };