Add support for small-model PIC for PowerPC.

Summary:
Large-model was added first.  With the addition of support for multiple PIC
models in LLVM, now add small-model PIC for 32-bit PowerPC, SysV4 ABI.  This
generates more optimal code, for shared libraries with less than about 16380
data objects.

Test Plan: Test cases added or updated

Reviewers: joerg, hfinkel

Reviewed By: hfinkel

Subscribers: jholewinski, mcrosier, emaste, llvm-commits

Differential Revision: http://reviews.llvm.org/D5399

llvm-svn: 221791

1 files changed, 75 insertions, 41 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp b/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
index 471780ac5a2..564887353dd 100644
--- a/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
+++ b/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
@@ -323,12 +323,35 @@ MCSymbol *PPCAsmPrinter::lookUpOrCreateTOCEntry(MCSymbol *Sym) {
 void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   MCInst TmpInst;
   bool isPPC64 = Subtarget.isPPC64();
+  bool isDarwin = Triple(TM.getTargetTriple()).isOSDarwin();
+  const Module *M = MF->getFunction()->getParent();
+  PICLevel::Level PL = M->getPICLevel();
   
   // Lower multi-instruction pseudo operations.
   switch (MI->getOpcode()) {
   default: break;
   case TargetOpcode::DBG_VALUE:
     llvm_unreachable("Should be handled target independently");
+  case PPC::MoveGOTtoLR: {
+    // Transform %LR = MoveGOTtoLR
+    // Into this: bl _GLOBAL_OFFSET_TABLE_@local-4
+    // _GLOBAL_OFFSET_TABLE_@local-4 (instruction preceding
+    // _GLOBAL_OFFSET_TABLE_) has exactly one instruction:
+    //      blrl
+    // This will return the pointer to _GLOBAL_OFFSET_TABLE_@local
+    MCSymbol *GOTSymbol =
+      OutContext.GetOrCreateSymbol(StringRef("_GLOBAL_OFFSET_TABLE_"));
+    const MCExpr *OffsExpr =
+      MCBinaryExpr::CreateSub(MCSymbolRefExpr::Create(GOTSymbol,
+                                                      MCSymbolRefExpr::VK_PPC_LOCAL,
+                                                      OutContext),
+                              MCConstantExpr::Create(4, OutContext),
+                              OutContext);
+
+    // Emit the 'bl'.
+    EmitToStreamer(OutStreamer, MCInstBuilder(PPC::BL).addExpr(OffsExpr));
+    return;
+  }
   case PPC::MovePCtoLR:
   case PPC::MovePCtoLR8: {
     // Transform %LR = MovePCtoLR
@@ -347,10 +370,14 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
     OutStreamer.EmitLabel(PICBase);
     return;
   }
-  case PPC::GetGBRO: {
+  case PPC::UpdateGBR: {
+    // Transform %Rd = UpdateGBR(%Rt, %Ri)
+    // Into: lwz %Rt, .L0$poff - .L0$pb(%Ri)
+    //       add %Rd, %Rt, %Ri
     // Get the offset from the GOT Base Register to the GOT
-    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, Subtarget.isDarwin());
-    MCSymbol *PICOffset = MF->getInfo<PPCFunctionInfo>()->getPICOffsetSymbol();
+    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, isDarwin);
+    MCSymbol *PICOffset =
+      MF->getInfo<PPCFunctionInfo>()->getPICOffsetSymbol();
     TmpInst.setOpcode(PPC::LWZ);
     const MCExpr *Exp =
       MCSymbolRefExpr::Create(PICOffset, MCSymbolRefExpr::VK_None, OutContext);
@@ -358,26 +385,26 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
       MCSymbolRefExpr::Create(MF->getPICBaseSymbol(),
                               MCSymbolRefExpr::VK_None,
                               OutContext);
-    const MCOperand MO = TmpInst.getOperand(1);
-    TmpInst.getOperand(1) = MCOperand::CreateExpr(MCBinaryExpr::CreateSub(Exp,
-                                                                          PB,
-                                                                          OutContext));
-    TmpInst.addOperand(MO);
+    const MCOperand TR = TmpInst.getOperand(1);
+    const MCOperand PICR = TmpInst.getOperand(0);
+
+    // Step 1: lwz %Rt, .L$poff - .L$pb(%Ri)
+    TmpInst.getOperand(1) =
+        MCOperand::CreateExpr(MCBinaryExpr::CreateSub(Exp, PB, OutContext));
+    TmpInst.getOperand(0) = TR;
+    TmpInst.getOperand(2) = PICR;
     EmitToStreamer(OutStreamer, TmpInst);
-    return;
-  }
-  case PPC::UpdateGBR: {
-    // Update the GOT Base Register to point to the GOT.  It may be possible to
-    // merge this with the PPC::GetGBRO, doing it all in one step.
-    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, Subtarget.isDarwin());
+
     TmpInst.setOpcode(PPC::ADD4);
-    TmpInst.addOperand(TmpInst.getOperand(0));
+    TmpInst.getOperand(0) = PICR;
+    TmpInst.getOperand(1) = TR;
+    TmpInst.getOperand(2) = PICR;
     EmitToStreamer(OutStreamer, TmpInst);
     return;
   }
   case PPC::LWZtoc: {
-    // Transform %X3 = LWZtoc <ga:@min1>, %X2
-    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, Subtarget.isDarwin());
+    // Transform %R3 = LWZtoc <ga:@min1>, %R2
+    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, isDarwin);
 
     // Change the opcode to LWZ, and the global address operand to be a
     // reference to the GOT entry we will synthesize later.
@@ -396,16 +423,23 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
     else if (MO.isBlockAddress())
       MOSymbol = GetBlockAddressSymbol(MO.getBlockAddress());
 
-    MCSymbol *TOCEntry = lookUpOrCreateTOCEntry(MOSymbol);
-
-    const MCExpr *Exp =
-      MCSymbolRefExpr::Create(TOCEntry, MCSymbolRefExpr::VK_None,
-                              OutContext);
-    const MCExpr *PB =
-      MCSymbolRefExpr::Create(OutContext.GetOrCreateSymbol(Twine(".L.TOC.")),
-                                                           OutContext);
-    Exp = MCBinaryExpr::CreateSub(Exp, PB, OutContext);
-    TmpInst.getOperand(1) = MCOperand::CreateExpr(Exp);
+    if (PL == PICLevel::Small) {
+      const MCExpr *Exp =
+        MCSymbolRefExpr::Create(MOSymbol, MCSymbolRefExpr::VK_GOT,
+                                OutContext);
+      TmpInst.getOperand(1) = MCOperand::CreateExpr(Exp);
+    } else {
+      MCSymbol *TOCEntry = lookUpOrCreateTOCEntry(MOSymbol);
+
+      const MCExpr *Exp =
+        MCSymbolRefExpr::Create(TOCEntry, MCSymbolRefExpr::VK_None,
+                                OutContext);
+      const MCExpr *PB =
+        MCSymbolRefExpr::Create(OutContext.GetOrCreateSymbol(Twine(".LTOC")),
+                                                             OutContext);
+      Exp = MCBinaryExpr::CreateSub(Exp, PB, OutContext);
+      TmpInst.getOperand(1) = MCOperand::CreateExpr(Exp);
+    }
     EmitToStreamer(OutStreamer, TmpInst);
     return;
   }
@@ -414,7 +448,7 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   case PPC::LDtocBA:
   case PPC::LDtoc: {
     // Transform %X3 = LDtoc <ga:@min1>, %X2
-    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, Subtarget.isDarwin());
+    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, isDarwin);
 
     // Change the opcode to LD, and the global address operand to be a
     // reference to the TOC entry we will synthesize later.
@@ -445,7 +479,7 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
       
   case PPC::ADDIStocHA: {
     // Transform %Xd = ADDIStocHA %X2, <ga:@sym>
-    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, Subtarget.isDarwin());
+    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, isDarwin);
 
     // Change the opcode to ADDIS8.  If the global address is external, has
     // common linkage, is a non-local function address, or is a jump table
@@ -491,7 +525,7 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   }
   case PPC::LDtocL: {
     // Transform %Xd = LDtocL <ga:@sym>, %Xs
-    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, Subtarget.isDarwin());
+    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, isDarwin);
 
     // Change the opcode to LD.  If the global address is external, has
     // common linkage, or is a jump table address, then reference the
@@ -533,7 +567,7 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   }
   case PPC::ADDItocL: {
     // Transform %Xd = ADDItocL %Xs, <ga:@sym>
-    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, Subtarget.isDarwin());
+    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, isDarwin);
 
     // Change the opcode to ADDI8.  If the global address is external, then
     // generate a TOC entry and reference that.  Otherwise reference the
@@ -584,7 +618,7 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   case PPC::LDgotTprelL:
   case PPC::LDgotTprelL32: {
     // Transform %Xd = LDgotTprelL <ga:@sym>, %Xs
-    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, Subtarget.isDarwin());
+    LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, isDarwin);
 
     // Change the opcode to LD.
     TmpInst.setOpcode(isPPC64 ? PPC::LD : PPC::LWZ);
@@ -808,7 +842,7 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   }
   }
 
-  LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, Subtarget.isDarwin());
+  LowerPPCMachineInstrToMCInst(MI, TmpInst, *this, isDarwin);
   EmitToStreamer(OutStreamer, TmpInst);
 }
 
@@ -824,16 +858,14 @@ void PPCLinuxAsmPrinter::EmitStartOfAsmFile(Module &M) {
   if (Subtarget.isPPC64() || TM.getRelocationModel() != Reloc::PIC_)
     return AsmPrinter::EmitStartOfAsmFile(M);
 
-  // FIXME: The use of .got2 assumes large GOT model (-fPIC), which is not
-  // optimal for some cases.  We should consider supporting small model (-fpic)
-  // as well in the future.
-  assert(TM.getCodeModel() != CodeModel::Small &&
-         "Small code model PIC is currently unsupported.");
+  if (M.getPICLevel() == PICLevel::Small)
+    return AsmPrinter::EmitStartOfAsmFile(M);
+
   OutStreamer.SwitchSection(OutContext.getELFSection(".got2",
          ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC,
          SectionKind::getReadOnly()));
 
-  MCSymbol *TOCSym = OutContext.GetOrCreateSymbol(Twine(".L.TOC."));
+  MCSymbol *TOCSym = OutContext.GetOrCreateSymbol(Twine(".LTOC"));
   MCSymbol *CurrentPos = OutContext.CreateTempSymbol();
 
   OutStreamer.EmitLabel(CurrentPos);
@@ -852,7 +884,9 @@ void PPCLinuxAsmPrinter::EmitStartOfAsmFile(Module &M) {
 
 void PPCLinuxAsmPrinter::EmitFunctionEntryLabel() {
   // linux/ppc32 - Normal entry label.
-  if (!Subtarget.isPPC64() && TM.getRelocationModel() != Reloc::PIC_)
+  if (!Subtarget.isPPC64() && 
+      (TM.getRelocationModel() != Reloc::PIC_ || 
+       MF->getFunction()->getParent()->getPICLevel() == PICLevel::Small))
     return AsmPrinter::EmitFunctionEntryLabel();
 
   if (!Subtarget.isPPC64()) {
@@ -864,7 +898,7 @@ void PPCLinuxAsmPrinter::EmitFunctionEntryLabel() {
 
       const MCExpr *OffsExpr =
         MCBinaryExpr::CreateSub(
-          MCSymbolRefExpr::Create(OutContext.GetOrCreateSymbol(Twine(".L.TOC.")),
+          MCSymbolRefExpr::Create(OutContext.GetOrCreateSymbol(Twine(".LTOC")),
                                                                OutContext),
                                   MCSymbolRefExpr::Create(PICBase, OutContext),
           OutContext);