Subzero. ARM32. Nonsfi.

src/IceTargetLoweringARM32.cpp

 //===- subzero/src/IceTargetLoweringARM32.cpp - ARM32 lowering ------------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 34 matching lines @@
   return ::Ice::ARM32::TargetDataARM32::create(Ctx);
 }
 
 std::unique_ptr<::Ice::TargetHeaderLowering>
 createTargetHeaderLowering(::Ice::GlobalContext *Ctx) {
   return ::Ice::ARM32::TargetHeaderARM32::create(Ctx);
 }
 
 void staticInit(::Ice::GlobalContext *Ctx) {
   ::Ice::ARM32::TargetARM32::staticInit(Ctx);
+  if (Ctx->getFlags().getUseNonsfi()) {
+    // In nonsfi, we need to reference the _GLOBAL_OFFSET_TABLE_ for accessing
+    // globals. The GOT is an external symbol (i.e., it is not defined in the
+    // pexe) so we need to register it as such so that ELF emission won't barf
+    // on an "unknown" symbol. The GOT is added to the External symbols list
+    // here because staticInit() is invoked in a single-thread context.
+    Ctx->getConstantExternSym(::Ice::GlobalOffsetTable);
+  }
 }
 
 } // end of namespace ARM32
 
 namespace Ice {
 namespace ARM32 {
 
 namespace {
 
 /// SizeOf is used to obtain the size of an initializer list as a constexpr
@@ skipping 206 matching lines @@
     ;
 std::array<uint32_t, NumVec128Args> Vec128ArgInitializer;
 
 IceString getRegClassName(RegClass C) {
   auto ClassNum = static_cast<RegARM32::RegClassARM32>(C);
   assert(ClassNum < RegARM32::RCARM32_NUM);
   switch (ClassNum) {
   default:
     assert(C < RC_Target);
     return regClassString(C);
-    // Add handling of new register classes below.
+  // Add handling of new register classes below.
+  case RegARM32::RCARM32_QtoS:
+    return "QtoS";
   }
 }
 
 } // end of anonymous namespace
 
 TargetARM32::TargetARM32(Cfg *Func)
     : TargetLowering(Func), NeedSandboxing(SandboxingType == ST_NaCl),
       CPUFeatures(Func->getContext()->getFlags()) {}
 
 void TargetARM32::staticInit(GlobalContext *Ctx) {
@@ skipping 400 matching lines @@
       Operand *TargetHelper = Ctx->getConstantExternSym(H_call_memset);
       auto *Call = Context.insert<InstCall>(MaxArgs, NoDest, TargetHelper,
                                             NoTailCall, IsTargetHelperCall);
       Call->addArg(IntrinsicCall->getArg(0));
       Call->addArg(ValExt);
       Call->addArg(IntrinsicCall->getArg(2));
       Instr->setDeleted();
       return;
     }
     case Intrinsics::NaClReadTP: {
-      if (NeedSandboxing) {
+      if (SandboxingType == ST_NaCl) {
         return;
       }
       static constexpr SizeT MaxArgs = 0;
       Operand *TargetHelper = Ctx->getConstantExternSym(H_call_read_tp);
       Context.insert<InstCall>(MaxArgs, Dest, TargetHelper, NoTailCall,
                                IsTargetHelperCall);
       Instr->setDeleted();
       return;
     }
     case Intrinsics::Setjmp: {
@@ skipping 22 matching lines @@
       PostIncrLoweringContext PostIncrement(Context);
       Inst *CurInstr = Context.getCur();
       if (auto *Call = llvm::dyn_cast<InstCall>(CurInstr)) {
         SizeT OutArgsSizeBytes = getCallStackArgumentsSizeBytes(Call);
         MaxOutArgsSizeBytes = std::max(MaxOutArgsSizeBytes, OutArgsSizeBytes);
       }
     }
   }
 }
 
+void TargetARM32::createGotPtr() {
+  if (SandboxingType != ST_Nonsfi) {
+    return;
+  }
+  GotPtr = Func->makeVariable(IceType_i32);
+}
+
+void TargetARM32::insertGotPtrInitPlaceholder() {
+  if (SandboxingType != ST_Nonsfi) {
+    return;
+  }
+  assert(GotPtr != nullptr);
+  // We add the two placeholder instructions here. The first fakedefs T, an
+  // infinite-weight temporary, while the second fakedefs the GotPtr "using" T.
+  // This is needed because the GotPtr initialization, if needed, will require
+  // a register:
+  //
+  //   movw     reg, _GLOBAL_OFFSET_TABLE_ - 16 - .
+  //   movt     reg, _GLOBAL_OFFSET_TABLE_ - 12 - .
+  //   add      reg, pc, reg
+  //   mov      GotPtr, reg
+  //
+  // If GotPtr is not used, then both these pseudo-instructions are dce'd.
+  Variable *T = makeReg(IceType_i32);
+  Context.insert<InstFakeDef>(T);
+  Context.insert<InstFakeDef>(GotPtr, T);
+}
+
+IceString TargetARM32::createGotoffRelocation(const ConstantRelocatable *CR) {
+  const IceString &CRName = CR->getName();
+  const IceString CRGotoffName =
+      "GOTOFF$" + Func->getFunctionName() + "$" + CRName;
+  if (KnownGotoffs.count(CRGotoffName) == 0) {
+    auto *Global = VariableDeclaration::create(Ctx);
+    Global->setIsConstant(true);
+    Global->setName(CRName);
+    Global->setSuppressMangling();
+
+    auto *Gotoff = VariableDeclaration::create(Ctx);
+    constexpr auto GotFixup = R_ARM_GOTOFF32;
+    Gotoff->setIsConstant(true);
+    Gotoff->setName(CRGotoffName);
+    Gotoff->setSuppressMangling();
+    Gotoff->addInitializer(VariableDeclaration::RelocInitializer::create(
+        Global, {RelocOffset::create(Ctx, 0)}, GotFixup));
+    Func->addGlobal(Gotoff);
+    KnownGotoffs.emplace(CRGotoffName);
+  }
+  return CRGotoffName;
+}
+
+void TargetARM32::materializeGotAddr(CfgNode *Node) {
+  if (SandboxingType != ST_Nonsfi) {
+    return;
+  }
+
+  // At first, we try to find the
+  //    GotPtr = def T
+  // pseudo-instruction that we placed for defining the got ptr. That
+  // instruction is not just a place-holder for defining the GotPtr (thus
+  // keeping liveness consistent), but it is also located at a point where it is
+  // safe to materialize the got addr -- i.e., before loading parameters to
+  // registers, but after moving register parameters from their home location.
+  InstFakeDef *DefGotPtr = nullptr;
+  for (auto &Inst : Node->getInsts()) {
+    auto *FakeDef = llvm::dyn_cast<InstFakeDef>(&Inst);
+    if (FakeDef != nullptr && FakeDef->getDest() == GotPtr) {
+      DefGotPtr = FakeDef;
+      break;
+    }
+  }
+
+  if (DefGotPtr == nullptr || DefGotPtr->isDeleted()) {
+    return;
+  }
+
+  // The got addr needs to be materialized at the same point where DefGotPtr
+  // lives.
+  Context.setInsertPoint(DefGotPtr);
+  assert(DefGotPtr->getSrcSize() == 1);
+  auto *T = llvm::cast<Variable>(DefGotPtr->getSrc(0));
+  loadNamedConstantRelocatablePIC(GlobalOffsetTable, T,
+                                  [this, T](Variable *PC) { _add(T, PC, T); });
+  _mov(GotPtr, T);
+  DefGotPtr->setDeleted();
+}
+
+void TargetARM32::loadNamedConstantRelocatablePIC(
+    const IceString &Name, Variable *Register,
+    std::function<void(Variable *PC)> Finish, bool SuppressMangling) {
+  assert(SandboxingType == ST_Nonsfi);
+  // We makeReg() here instead of getPhysicalRegister() because the latter ends
+  // up creating multi-blocks temporaries that liveness fails to validate.
+  auto *PC = makeReg(IceType_i32, RegARM32::Reg_pc);
+
+  auto *AddPcReloc = RelocOffset::create(Ctx);
+  AddPcReloc->setSubtract(true);
+  auto *AddPcLabel = InstARM32Label::create(Func, this);
+  AddPcLabel->setRelocOffset(AddPcReloc);
+
+  const IceString EmitText = Name;
+  // We need a -8 in the relocation expression to account for the pc's value
+  // read by the first instruction emitted in Finish(PC).
+  auto *Imm8 = RelocOffset::create(Ctx, -8);
+
+  auto *MovwReloc = RelocOffset::create(Ctx);
+  auto *MovwLabel = InstARM32Label::create(Func, this);
+  MovwLabel->setRelocOffset(MovwReloc);
+
+  auto *MovtReloc = RelocOffset::create(Ctx);
+  auto *MovtLabel = InstARM32Label::create(Func, this);
+  MovtLabel->setRelocOffset(MovtReloc);
+
+  // The EmitString for these constant relocatables have hardcoded offsets
+  // attached to them. This could be dangerous if, e.g., we ever implemented
+  // instruction scheduling but llvm-mc currently does not support
+  //
+  //   movw reg, #:lower16:(Symbol - Label - Number)
+  //   movt reg, #:upper16:(Symbol - Label - Number)
+  //
+  // relocations.
+  auto *CRLower = Ctx->getConstantSym({MovwReloc, AddPcReloc, Imm8}, Name,
+                                      EmitText + " -16", SuppressMangling);
+  auto *CRUpper = Ctx->getConstantSym({MovtReloc, AddPcReloc, Imm8}, Name,
+                                      EmitText + " -12", SuppressMangling);
+
+  Context.insert(MovwLabel);
+  _movw(Register, CRLower);
+  Context.insert(MovtLabel);
+  _movt(Register, CRUpper);
+  // PC = fake-def to keep liveness consistent.
+  Context.insert<InstFakeDef>(PC);
+  Context.insert(AddPcLabel);
+  Finish(PC);
+}
+
 void TargetARM32::translateO2() {
   TimerMarker T(TimerStack::TT_O2, Func);
 
-  // TODO(stichnot): share passes with X86?
+  // TODO(stichnot): share passes with other targets?
   // https://code.google.com/p/nativeclient/issues/detail?id=4094
+  if (SandboxingType == ST_Nonsfi) {
+    createGotPtr();
+  }
   genTargetHelperCalls();
   findMaxStackOutArgsSize();
 
   // Do not merge Alloca instructions, and lay out the stack.
   static constexpr bool SortAndCombineAllocas = true;
   Func->processAllocas(SortAndCombineAllocas);
   Func->dump("After Alloca processing");
 
   if (!Ctx->getFlags().getPhiEdgeSplit()) {
     // Lower Phi instructions.
@@ skipping 26 matching lines @@
     return;
 
   // TODO: It should be sufficient to use the fastest liveness calculation,
   // i.e. livenessLightweight(). However, for some reason that slows down the
   // rest of the translation. Investigate.
   Func->liveness(Liveness_Basic);
   if (Func->hasError())
     return;
   Func->dump("After ARM32 address mode opt");
 
+  if (SandboxingType == ST_Nonsfi) {
+    insertGotPtrInitPlaceholder();
+  }
   Func->genCode();
   if (Func->hasError())
     return;
   Func->dump("After ARM32 codegen");
 
   // Register allocation. This requires instruction renumbering and full
   // liveness analysis.
   Func->renumberInstructions();
   if (Func->hasError())
     return;
@@ skipping 44 matching lines @@
 
   // Nop insertion
   if (Ctx->getFlags().shouldDoNopInsertion()) {
     Func->doNopInsertion();
   }
 }
 
 void TargetARM32::translateOm1() {
   TimerMarker T(TimerStack::TT_Om1, Func);
 
-  // TODO: share passes with X86?
+  // TODO(stichnot): share passes with other targets?
+  if (SandboxingType == ST_Nonsfi) {
+    createGotPtr();
+  }
+
   genTargetHelperCalls();
   findMaxStackOutArgsSize();
 
   // Do not merge Alloca instructions, and lay out the stack.
   static constexpr bool DontSortAndCombineAllocas = false;
   Func->processAllocas(DontSortAndCombineAllocas);
   Func->dump("After Alloca processing");
 
   Func->placePhiLoads();
   if (Func->hasError())
     return;
   Func->placePhiStores();
   if (Func->hasError())
     return;
   Func->deletePhis();
   if (Func->hasError())
     return;
   Func->dump("After Phi lowering");
 
   Func->doArgLowering();
 
+  if (SandboxingType == ST_Nonsfi) {
+    insertGotPtrInitPlaceholder();
+  }
   Func->genCode();
   if (Func->hasError())
     return;
   Func->dump("After initial ARM32 codegen");
 
   regAlloc(RAK_InfOnly);
   if (Func->hasError())
     return;
 
   copyRegAllocFromInfWeightVariable64On32(Func->getVariables());
@@ skipping 477 matching lines @@
   Ctx->statsUpdateFrameBytes(SpillAreaSizeBytes);
 
   // Fill in stack offsets for stack args, and copy args into registers for
   // those that were register-allocated. Args are pushed right to left, so
   // Arg[0] is closest to the stack/frame pointer.
   Variable *FramePtr = getPhysicalRegister(getFrameOrStackReg());
   size_t BasicFrameOffset = PreservedRegsSizeBytes;
   if (!UsesFramePointer)
     BasicFrameOffset += SpillAreaSizeBytes;
 
+  materializeGotAddr(Node);
+
   const VarList &Args = Func->getArgs();
   size_t InArgsSizeBytes = 0;
   TargetARM32::CallingConv CC;
   for (Variable *Arg : Args) {
     int32_t DummyReg;
     const Type Ty = Arg->getType();
 
     // Skip arguments passed in registers.
     if (isScalarIntegerType(Ty)) {
       if (CC.argInGPR(Ty, &DummyReg)) {
@@ skipping 2104 matching lines @@
       ReturnReg = makeReg(Dest->getType(), RegARM32::Reg_q0);
       break;
     }
   }
 
   // Note: To allow far calls, even for constant relocatables, we force
   // the call target into a register, and make an indirect call.
   CallTarget = legalizeToReg(CallTarget);
 
   // Copy arguments to be passed in registers to the appropriate registers.
+  CfgVector<Variable *> RegArgs;
   for (auto &FPArg : FPArgs) {
-    Variable *Reg = legalizeToReg(FPArg.first, FPArg.second);
-    Context.insert<InstFakeUse>(Reg);
+    RegArgs.emplace_back(legalizeToReg(FPArg.first, FPArg.second));
   }
   for (auto &GPRArg : GPRArgs) {
-    Variable *Reg = legalizeToReg(GPRArg.first, GPRArg.second);
-    // Generate a FakeUse of register arguments so that they do not get dead
-    // code eliminated as a result of the FakeKill of scratch registers after
-    // the call.
-    Context.insert<InstFakeUse>(Reg);
+    RegArgs.emplace_back(legalizeToReg(GPRArg.first, GPRArg.second));
+  }
+
+  // Generate a FakeUse of register arguments so that they do not get dead code
+  // eliminated as a result of the FakeKill of scratch registers after the call.
+  // These fake-uses need to be placed here to avoid argument registers from
+  // being used during the legalizeToReg() calls above.
+  for (auto *RegArg : RegArgs) {
+    Context.insert<InstFakeUse>(RegArg);
   }
 
   InstARM32Call *NewCall =
       Sandboxer(this, InstBundleLock::Opt_AlignToEnd).bl(ReturnReg, CallTarget);
 
   if (ReturnRegHi)
     Context.insert<InstFakeDef>(ReturnRegHi);
 
   // Insert a register-kill pseudo instruction.
   Context.insert<InstFakeKill>(NewCall);
@@ skipping 384 matching lines @@
   CondARM32::Cond CC0;
   CondARM32::Cond CC1;
 } TableFcmp[] = {
 #define X(val, CC0, CC1)                                                       \
   { CondARM32::CC0, CondARM32::CC1 }                                           \
   ,
     FCMPARM32_TABLE
 #undef X
 };
 
-bool isFloatingPointZero(Operand *Src) {
-  if (const auto *F32 = llvm::dyn_cast<ConstantFloat>(Src)) {
+bool isFloatingPointZero(const Operand *Src) {
+  if (const auto *F32 = llvm::dyn_cast<const ConstantFloat>(Src)) {
     return Utils::isPositiveZero(F32->getValue());
   }
 
-  if (const auto *F64 = llvm::dyn_cast<ConstantDouble>(Src)) {
+  if (const auto *F64 = llvm::dyn_cast<const ConstantDouble>(Src)) {
     return Utils::isPositiveZero(F64->getValue());
   }
 
   return false;
 }
 } // end of anonymous namespace
 
 TargetARM32::CondWhenTrue TargetARM32::lowerFcmpCond(const InstFcmp *Instr) {
   InstFcmp::FCond Condition = Instr->getCondition();
   switch (Condition) {
@@ skipping 914 matching lines @@
   case Intrinsics::Memcpy: {
     llvm::report_fatal_error("memcpy should have been prelowered.");
   }
   case Intrinsics::Memmove: {
     llvm::report_fatal_error("memmove should have been prelowered.");
   }
   case Intrinsics::Memset: {
     llvm::report_fatal_error("memmove should have been prelowered.");
   }
   case Intrinsics::NaClReadTP: {
-    if (!NeedSandboxing) {
+    if (SandboxingType != ST_NaCl) {
       llvm::report_fatal_error("nacl-read-tp should have been prelowered.");
     }
     Variable *TP = legalizeToReg(OperandARM32Mem::create(
         Func, getPointerType(), getPhysicalRegister(RegARM32::Reg_r9),
         llvm::cast<ConstantInteger32>(Ctx->getConstantZero(IceType_i32))));
     _mov(Dest, TP);
     return;
   }
   case Intrinsics::Setjmp: {
     llvm::report_fatal_error("setjmp should have been prelowered.");
@@ skipping 639 matching lines @@
     _cmp(Src0Var, Value);
     _br(Instr->getLabel(I), CondARM32::EQ);
   }
   _br(Instr->getLabelDefault());
 }
 
 void TargetARM32::lowerUnreachable(const InstUnreachable * /*Instr*/) {
   _trap();
 }
 
+namespace {
+// Returns whether Opnd needs the GOT address. Currently, ConstantRelocatables,
+// and fp constants will need access to the GOT address.
+bool operandNeedsGot(const Operand *Opnd) {
+  if (llvm::isa<ConstantRelocatable>(Opnd)) {
+    return true;
+  }
+
+  const auto *F64 = llvm::dyn_cast<ConstantDouble>(Opnd);
+  if (F64 != nullptr || llvm::isa<ConstantFloat>(Opnd)) {
+    uint32_t _;
+    return !OperandARM32FlexFpImm::canHoldImm(Opnd, &_);
+  }
+
+  if (F64 != nullptr) {

[Jim Stichnoth, 2016/02/10 17:00:21]

This doesn't look right.  If F64!=nullptr, it should have already returned
above.

[John, 2016/02/10 23:38:21]

Done.

+    return !isFloatingPointZero(F64);
+  }
+
+  return false;
+}
+
+// Returns whether Phi needs the GOT address (which it does if any of its
+// operands needs the GOT address.)
+bool phiNeedsGot(const InstPhi *Phi) {
+  if (Phi->isDeleted()) {
+    return false;
+  }
+
+  for (SizeT I = 0; I < Phi->getSrcSize(); ++I) {
+    if (operandNeedsGot(Phi->getSrc(I))) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+// Returns whether **any** phi in Node needs the GOT address.
+bool anyPhiInNodeNeedsGot(CfgNode *Node) {
+  for (auto &Inst : Node->getPhis()) {
+    if (phiNeedsGot(llvm::cast<InstPhi>(&Inst))) {
+      return true;
+    }
+  }
+  return false;
+}
+
+} // end of anonymous namespace
+
 void TargetARM32::prelowerPhis() {
-  PhiLowering::prelowerPhis32Bit<TargetARM32>(this, Context.getNode(), Func);
+  CfgNode *Node = Context.getNode();
+
+  if (SandboxingType == ST_Nonsfi) {
+    assert(GotPtr != nullptr);
+    if (anyPhiInNodeNeedsGot(Node)) {
+      // If any phi instruction needs the GOT address, we place a
+      //   fake-use GotPtr
+      // in Node to prevent the GotPtr's initialization from being dead code
+      // eliminated.
+      Node->getInsts().push_front(InstFakeUse::create(Func, GotPtr));
+    }
+  }
+
+  PhiLowering::prelowerPhis32Bit(this, Node, Func);
 }
 
 Variable *TargetARM32::makeVectorOfZeros(Type Ty, int32_t RegNum) {
   Variable *Reg = makeReg(Ty, RegNum);
   Context.insert<InstFakeDef>(Reg);
   assert(isVectorType(Ty));
   _veor(Reg, Reg, Reg);
   return Reg;
 }
 
@@ skipping 142 matching lines @@
         uint32_t UpperBits = (Value >> 16) & 0xFFFF;
         _movw(Reg,
               UpperBits != 0 ? Ctx->getConstantInt32(Value & 0xFFFF) : C32);
         if (UpperBits != 0) {
           _movt(Reg, Ctx->getConstantInt32(UpperBits));
         }
         return Reg;
       }
     } else if (auto *C = llvm::dyn_cast<ConstantRelocatable>(From)) {
       Variable *Reg = makeReg(Ty, RegNum);
-      _movw(Reg, C);
-      _movt(Reg, C);
+      if (SandboxingType != ST_Nonsfi) {
+        _movw(Reg, C);
+        _movt(Reg, C);
+      } else {
+        auto *GotAddr = legalizeToReg(GotPtr);
+        const IceString CGotoffName = createGotoffRelocation(C);
+        loadNamedConstantRelocatablePIC(
+            CGotoffName, Reg, [this, Reg](Variable *PC) {
+              _ldr(Reg, OperandARM32Mem::create(Func, IceType_i32, PC, Reg));
+            });
+        _add(Reg, GotAddr, Reg);
+      }
       return Reg;
     } else {
       assert(isScalarFloatingType(Ty));
       uint32_t ModifiedImm;
       if (OperandARM32FlexFpImm::canHoldImm(From, &ModifiedImm)) {
         Variable *T = makeReg(Ty, RegNum);
         _mov(T,
              OperandARM32FlexFpImm::create(Func, From->getType(), ModifiedImm));
         return T;
       }
 
       if (Ty == IceType_f64 && isFloatingPointZero(From)) {
         // Use T = T ^ T to load a 64-bit fp zero. This does not work for f32
         // because ARM does not have a veor instruction with S registers.
         Variable *T = makeReg(IceType_f64, RegNum);
         Context.insert<InstFakeDef>(T);
         _veor(T, T, T);
         return T;
       }
 
       // Load floats/doubles from literal pool.
       std::string Buffer;
       llvm::raw_string_ostream StrBuf(Buffer);
       llvm::cast<Constant>(From)->emitPoolLabel(StrBuf, Ctx);
       llvm::cast<Constant>(From)->setShouldBePooled(true);
       Constant *Offset = Ctx->getConstantSym(0, StrBuf.str(), true);
-      Variable *BaseReg = makeReg(getPointerType());
-      _movw(BaseReg, Offset);
-      _movt(BaseReg, Offset);
+      Variable *BaseReg = nullptr;
+      if (SandboxingType == ST_Nonsfi) {
+        // vldr does not support the [base, index] addressing mode, so we need
+        // to legalize Offset to a register. Otherwise, we could simply
+        //   vldr dest, [got, reg(Offset)]
+        BaseReg = legalizeToReg(Offset);
+      } else {
+        BaseReg = makeReg(getPointerType());
+        _movw(BaseReg, Offset);
+        _movt(BaseReg, Offset);
+      }
       From = formMemoryOperand(BaseReg, Ty);
       return copyToReg(From, RegNum);
     }
   }
 
   if (auto *Var = llvm::dyn_cast<Variable>(From)) {
     if (Var->isRematerializable()) {
       if (Allowed & Legal_Rematerializable) {
         return From;
       }
@@ skipping 863 matching lines @@
   Str << ".eabi_attribute 14, 3   @ Tag_ABI_PCS_R9_use: Not used\n";
 }
 
 llvm::SmallBitVector TargetARM32::TypeToRegisterSet[RegARM32::RCARM32_NUM];
 llvm::SmallBitVector
     TargetARM32::TypeToRegisterSetUnfiltered[RegARM32::RCARM32_NUM];
 llvm::SmallBitVector TargetARM32::RegisterAliases[RegARM32::Reg_NUM];
 
 } // end of namespace ARM32
 } // end of namespace Ice