Rebased PNaCl localmods in LLVM to 223109

lib/Transforms/NaCl/ExpandTls.cpp

+//===- ExpandTls.cpp - Convert TLS variables to a concrete layout----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass expands out uses of thread-local (TLS) variables into
+// more primitive operations.
+//
+// A reference to the address of a TLS variable is expanded into code
+// which gets the current thread's thread pointer using
+// @llvm.nacl.read.tp() and adds a fixed offset.
+//
+// This pass allocates the offsets (relative to the thread pointer)
+// that will be used for TLS variables.  It sets up the global
+// variables __tls_template_start, __tls_template_end etc. to contain
+// a template for initializing TLS variables' values for each thread.
+// This is a task normally performed by the linker in ELF systems.
+//
+//===----------------------------------------------------------------------===//
+
+#include <vector>
+
+#include "llvm/Pass.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Transforms/NaCl.h"
+
+using namespace llvm;
+
+namespace {
+  struct VarInfo {
+    GlobalVariable *TlsVar;
+    bool IsBss; // Whether variable is in zero-intialized part of template
+    int TemplateIndex;
+  };
+
+  class PassState {
+  public:
+    PassState(Module *M): M(M), DL(M), Offset(0), Alignment(1) {}
+
+    Module *M;
+    DataLayout DL;
+    uint64_t Offset;
+    // 'Alignment' is the maximum variable alignment seen so far, in
+    // bytes.  After visiting all TLS variables, this is the overall
+    // alignment required for the TLS template.
+    uint32_t Alignment;
+  };
+
+  class ExpandTls : public ModulePass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    ExpandTls() : ModulePass(ID) {
+      initializeExpandTlsPass(*PassRegistry::getPassRegistry());
+    }
+
+    virtual bool runOnModule(Module &M);
+  };
+}
+
+char ExpandTls::ID = 0;
+INITIALIZE_PASS(ExpandTls, "nacl-expand-tls",
+                "Expand out TLS variables and fix TLS variable layout",
+                false, false)
+
+static void setGlobalVariableValue(Module &M, const char *Name,
+                                   Constant *Value) {
+  if (GlobalVariable *Var = M.getNamedGlobal(Name)) {
+    if (Var->hasInitializer()) {
+      report_fatal_error(std::string("Variable ") + Name +
+                         " already has an initializer");
+    }
+    Var->replaceAllUsesWith(ConstantExpr::getBitCast(Value, Var->getType()));
+    Var->eraseFromParent();
+  }
+}
+
+// Insert alignment padding into the TLS template.
+static void padToAlignment(PassState *State,
+                           std::vector<Type*> *FieldTypes,
+                           std::vector<Constant*> *FieldValues,
+                           unsigned Alignment) {
+  if ((State->Offset & (Alignment - 1)) != 0) {
+    unsigned PadSize = Alignment - (State->Offset & (Alignment - 1));
+    Type *i8 = Type::getInt8Ty(State->M->getContext());
+    Type *PadType = ArrayType::get(i8, PadSize);
+    FieldTypes->push_back(PadType);
+    if (FieldValues)
+      FieldValues->push_back(Constant::getNullValue(PadType));
+    State->Offset += PadSize;
+  }
+  if (State->Alignment < Alignment) {
+    State->Alignment = Alignment;
+  }
+}
+
+static void addVarToTlsTemplate(PassState *State,
+                                std::vector<Type*> *FieldTypes,
+                                std::vector<Constant*> *FieldValues,
+                                GlobalVariable *TlsVar) {
+  unsigned Alignment = State->DL.getPreferredAlignment(TlsVar);
+  padToAlignment(State, FieldTypes, FieldValues, Alignment);
+
+  FieldTypes->push_back(TlsVar->getType()->getElementType());
+  if (FieldValues)
+    FieldValues->push_back(TlsVar->getInitializer());
+  State->Offset +=
+      State->DL.getTypeAllocSize(TlsVar->getType()->getElementType());
+}
+
+static PointerType *buildTlsTemplate(Module &M, std::vector<VarInfo> *TlsVars) {
+  std::vector<Type*> FieldBssTypes;
+  std::vector<Type*> FieldInitTypes;
+  std::vector<Constant*> FieldInitValues;
+  PassState State(&M);
+
+  for (Module::global_iterator GV = M.global_begin();
+       GV != M.global_end();
+       ++GV) {
+    if (GV->isThreadLocal()) {
+      if (!GV->hasInitializer()) {
+        // Since this is a whole-program transformation, "extern" TLS
+        // variables are not allowed at this point.
+        report_fatal_error(std::string("TLS variable without an initializer: ")
+                           + GV->getName());
+      }
+      if (!GV->getInitializer()->isNullValue()) {
+        addVarToTlsTemplate(&State, &FieldInitTypes,
+                            &FieldInitValues, GV);
+        VarInfo Info;
+        Info.TlsVar = GV;
+        Info.IsBss = false;
+        Info.TemplateIndex = FieldInitTypes.size() - 1;
+        TlsVars->push_back(Info);
+      }
+    }
+  }
+  // Handle zero-initialized TLS variables in a second pass, because
+  // these should follow non-zero-initialized TLS variables.
+  for (Module::global_iterator GV = M.global_begin();
+       GV != M.global_end();
+       ++GV) {
+    if (GV->isThreadLocal() && GV->getInitializer()->isNullValue()) {
+      addVarToTlsTemplate(&State, &FieldBssTypes, NULL, GV);
+      VarInfo Info;
+      Info.TlsVar = GV;
+      Info.IsBss = true;
+      Info.TemplateIndex = FieldBssTypes.size() - 1;
+      TlsVars->push_back(Info);
+    }
+  }
+  // Add final alignment padding so that
+  //   (struct tls_struct *) __nacl_read_tp() - 1
+  // gives the correct, aligned start of the TLS variables given the
+  // x86-style layout we are using.  This requires some more bytes to
+  // be memset() to zero at runtime.  This wastage doesn't seem
+  // important gives that we're not trying to optimize packing by
+  // reordering to put similarly-aligned variables together.
+  padToAlignment(&State, &FieldBssTypes, NULL, State.Alignment);
+
+  // We create the TLS template structs as "packed" because we insert
+  // alignment padding ourselves, and LLVM's implicit insertion of
+  // padding would interfere with ours.  tls_bss_template can start at
+  // a non-aligned address immediately following the last field in
+  // tls_init_template.
+  StructType *InitTemplateType =
+      StructType::create(M.getContext(), "tls_init_template");
+  InitTemplateType->setBody(FieldInitTypes, /*isPacked=*/true);
+  StructType *BssTemplateType =
+      StructType::create(M.getContext(), "tls_bss_template");
+  BssTemplateType->setBody(FieldBssTypes, /*isPacked=*/true);
+
+  StructType *TemplateType = StructType::create(M.getContext(), "tls_struct");
+  SmallVector<Type*, 2> TemplateTopFields;
+  TemplateTopFields.push_back(InitTemplateType);
+  TemplateTopFields.push_back(BssTemplateType);
+  TemplateType->setBody(TemplateTopFields, /*isPacked=*/true);
+  PointerType *TemplatePtrType = PointerType::get(TemplateType, 0);
+
+  // We define the following symbols, which are the same as those
+  // defined by NaCl's original customized binutils linker scripts:
+  //   __tls_template_start
+  //   __tls_template_tdata_end
+  //   __tls_template_end
+  // We also define __tls_template_alignment, which was not defined by
+  // the original linker scripts.
+
+  const char *StartSymbol = "__tls_template_start";
+  Constant *TemplateData = ConstantStruct::get(InitTemplateType,
+                                               FieldInitValues);
+  GlobalVariable *TemplateDataVar =
+      new GlobalVariable(M, InitTemplateType, /*isConstant=*/true,
+                         GlobalValue::InternalLinkage, TemplateData);
+  setGlobalVariableValue(M, StartSymbol, TemplateDataVar);
+  TemplateDataVar->setName(StartSymbol);
+
+  Constant *TdataEnd = ConstantExpr::getGetElementPtr(
+      TemplateDataVar,
+      ConstantInt::get(M.getContext(), APInt(32, 1)));
+  setGlobalVariableValue(M, "__tls_template_tdata_end", TdataEnd);
+
+  Constant *TotalEnd = ConstantExpr::getGetElementPtr(
+      ConstantExpr::getBitCast(TemplateDataVar, TemplatePtrType),
+      ConstantInt::get(M.getContext(), APInt(32, 1)));
+  setGlobalVariableValue(M, "__tls_template_end", TotalEnd);
+
+  const char *AlignmentSymbol = "__tls_template_alignment";
+  Type *i32 = Type::getInt32Ty(M.getContext());
+  GlobalVariable *AlignmentVar = new GlobalVariable(
+      M, i32, /*isConstant=*/true,
+      GlobalValue::InternalLinkage,
+      ConstantInt::get(M.getContext(), APInt(32, State.Alignment)));
+  setGlobalVariableValue(M, AlignmentSymbol, AlignmentVar);
+  AlignmentVar->setName(AlignmentSymbol);
+
+  return TemplatePtrType;
+}
+
+static void rewriteTlsVars(Module &M, std::vector<VarInfo> *TlsVars,
+                           PointerType *TemplatePtrType) {
+  // Set up the intrinsic that reads the thread pointer.
+  Function *ReadTpFunc = Intrinsic::getDeclaration(&M, Intrinsic::nacl_read_tp);
+
+  for (std::vector<VarInfo>::iterator VarInfo = TlsVars->begin();
+       VarInfo != TlsVars->end();
+       ++VarInfo) {
+    GlobalVariable *Var = VarInfo->TlsVar;
+    while (Var->hasNUsesOrMore(1)) {
+      Use *U = &*Var->use_begin();
+      Instruction *InsertPt = PhiSafeInsertPt(U);
+      Value *RawThreadPtr = CallInst::Create(ReadTpFunc, "tls_raw", InsertPt);
+      Value *TypedThreadPtr = new BitCastInst(RawThreadPtr, TemplatePtrType,
+                                              "tls_struct", InsertPt);
+      SmallVector<Value*, 3> Indexes;
+      // We use -1 because we use the x86-style TLS layout in which
+      // the TLS data is stored at addresses below the thread pointer.
+      // This is largely because a check in nacl_irt_thread_create()
+      // in irt/irt_thread.c requires the thread pointer to be a
+      // self-pointer on x86-32.
+      // TODO(mseaborn): I intend to remove that check because it is
+      // non-portable.  In the mean time, we want PNaCl pexes to work
+      // in older Chromium releases when translated to nexes.
+      Indexes.push_back(ConstantInt::get(
+          M.getContext(), APInt(32, -1)));
+      Indexes.push_back(ConstantInt::get(
+          M.getContext(), APInt(32, VarInfo->IsBss ? 1 : 0)));
+      Indexes.push_back(ConstantInt::get(
+          M.getContext(), APInt(32, VarInfo->TemplateIndex)));
+      Value *TlsField = GetElementPtrInst::Create(TypedThreadPtr, Indexes,
+                                                  "field", InsertPt);
+      PhiSafeReplaceUses(U, TlsField);
+    }
+    VarInfo->TlsVar->eraseFromParent();
+  }
+}
+
+static void replaceFunction(Module &M, const char *Name, Value *NewFunc) {
+  if (Function *Func = M.getFunction(Name)) {
+    if (Func->hasLocalLinkage())
+      return;
+    if (!Func->isDeclaration())
+      report_fatal_error(std::string("Function already defined: ") + Name);
+    Func->replaceAllUsesWith(NewFunc);
+    Func->eraseFromParent();
+  }
+}
+
+// Provide fixed definitions for NaCl's TLS layout functions,
+// __nacl_tp_*().  We adopt the x86-style layout: ExpandTls will
+// output a program that uses the x86-style layout wherever it runs.
+//
+// This overrides the architecture-specific definitions of
+// __nacl_tp_*() that PNaCl's native support code makes available to
+// non-ABI-stable code.
+static void defineTlsLayoutFunctions(Module &M) {
+  Type *i32 = Type::getInt32Ty(M.getContext());
+  SmallVector<Type*, 1> ArgTypes;
+  ArgTypes.push_back(i32);
+  FunctionType *FuncType = FunctionType::get(i32, ArgTypes, /*isVarArg=*/false);
+  Function *NewFunc;
+  BasicBlock *BB;
+
+  // Define the function as follows:
+  //   uint32_t __nacl_tp_tdb_offset(uint32_t tdb_size) {
+  //     return 0;
+  //   }
+  // This means the thread pointer points to the TDB.
+  NewFunc = Function::Create(FuncType, GlobalValue::InternalLinkage,
+                             "nacl_tp_tdb_offset", &M);
+  BB = BasicBlock::Create(M.getContext(), "entry", NewFunc);
+  ReturnInst::Create(M.getContext(),
+                     ConstantInt::get(M.getContext(), APInt(32, 0)), BB);
+  replaceFunction(M, "__nacl_tp_tdb_offset", NewFunc);
+
+  // Define the function as follows:
+  //   uint32_t __nacl_tp_tls_offset(uint32_t tls_size) {
+  //     return -tls_size;
+  //   }
+  // This means the TLS variables are stored below the thread pointer.
+  NewFunc = Function::Create(FuncType, GlobalValue::InternalLinkage,
+                             "nacl_tp_tls_offset", &M);
+  BB = BasicBlock::Create(M.getContext(), "entry", NewFunc);
+  Value *Arg = NewFunc->arg_begin();
+  Arg->setName("size");
+  Value *Result = BinaryOperator::CreateNeg(Arg, "result", BB);
+  ReturnInst::Create(M.getContext(), Result, BB);
+  replaceFunction(M, "__nacl_tp_tls_offset", NewFunc);
+}
+
+bool ExpandTls::runOnModule(Module &M) {
+  ModulePass *Pass = createExpandTlsConstantExprPass();
+  Pass->runOnModule(M);
+  delete Pass;
+
+  std::vector<VarInfo> TlsVars;
+  PointerType *TemplatePtrType = buildTlsTemplate(M, &TlsVars);
+  rewriteTlsVars(M, &TlsVars, TemplatePtrType);
+
+  defineTlsLayoutFunctions(M);
+
+  return true;
+}
+
+ModulePass *llvm::createExpandTlsPass() {
+  return new ExpandTls();
+}