Concurrency support for PNaCl ABI

lib/Transforms/NaCl/FreezeAtomics.cpp

+//===- FreezeAtomics.cpp - Stabilize instructions used for concurrency ----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass encodes atomics, volatiles and fences using NaCl intrinsics
+// instead of LLVM's regular IR instructions.
+//
+// All of the above are transformed into one of the @nacl.atomic.<size>
+// intrinsics.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/NaCl.h"
+#include "llvm/InstVisitor.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/NaCl.h"
+
+using namespace llvm;
+
+namespace {
+class FreezeAtomics : public ModulePass {
+ public:
+  static char ID; // Pass identification, replacement for typeid
+  FreezeAtomics() : ModulePass(ID) {
+    // This is a module pass because it may have to introduce
+    // intrinsic declarations into the module and modify a global function.
+    initializeFreezeAtomicsPass(*PassRegistry::getPassRegistry());
+  }
+
+  virtual bool runOnModule(Module &M);
+};
+
+class AtomicVisitor : public InstVisitor<AtomicVisitor> {
+  Module &M;
+  LLVMContext &C;
+  bool ModifiedModule;
+  struct {
+    Function *F;
+    unsigned BitSize;
+  } AtomicFunctions[NaCl::NumAtomicIntrinsics];
+
+  AtomicVisitor();
+  AtomicVisitor(const AtomicVisitor&);
+  AtomicVisitor &operator=(const AtomicVisitor&);
+
+  NaCl::MemoryOrder freezeMemoryOrdering(llvm::AtomicOrdering AO) const;
+  bool sizeMatchesType(const Instruction &I, unsigned S, const Type *T) const;
+  Function *atomicIntrinsic(const Instruction &I, unsigned AtomicBitSize);
+  void replaceWithAtomicIntrinsic(
+      Instruction &I, const Type *T, unsigned Size, NaCl::AtomicOperation O,
+      Value *Loc, Value *Val, Value *Old, AtomicOrdering AO);
+
+  // Most atomics deal with at least one pointer, this struct automates
+  // some of this and has generic sanity checks.

[Derek Schuff, 2013/06/26 17:03:29]

maybe also mention that T should be an atomic LoadInst or StoreInst

[JF, 2013/06/26 23:41:12]

I'm not sure I understand: T needs to be an Instruction, with at least
getPointerOperand and getPointerAddressSpace. I've renamed T and updated the
comment to reflect this, let me know if you meant something else.

+  template<class T>
+  struct PointerHelper {
+    Value *P;
+    Type *PET;
+    unsigned Size;
+    Value *Zero;
+    PointerHelper(const AtomicVisitor &AV, T &I)
+        : P(I.getPointerOperand()) {
+      if (I.getPointerAddressSpace() != 0) {
+        errs() << "Unhandled: " << I << '\n';
+        report_fatal_error("unhandled pointer address space for atomic");
+      }
+      assert(P->getType()->isPointerTy() && "expected a pointer");
+      PET = P->getType()->getPointerElementType();
+      Size = PET->getIntegerBitWidth();
+      if (!AV.sizeMatchesType(I, Size, PET)) {
+        errs() << "Unhandled: " << I << '\n';
+        report_fatal_error("must have integer type of the right size");
+      }
+      Zero = ConstantInt::get(PET, 0);
+    }
+  };
+
+ public:
+  AtomicVisitor(Module &M)
+      : M(M), C(M.getContext()), ModifiedModule(false) {
+    for (size_t i = 0; i != NaCl::NumAtomicIntrinsics; ++i) {
+      AtomicFunctions[i].F =
+          Intrinsic::getDeclaration(&M, NaCl::AtomicIntrinsics[i].ID);
+      AtomicFunctions[i].BitSize = NaCl::AtomicIntrinsics[i].BitSize;
+    }
+  }
+  ~AtomicVisitor() {}
+  bool modifiedModule() const { return ModifiedModule; }
+
+  void visitLoadInst(LoadInst &I);
+  void visitStoreInst(StoreInst &I);
+  void visitAtomicCmpXchgInst(AtomicCmpXchgInst &I);
+  void visitAtomicRMWInst(AtomicRMWInst &I);
+  void visitFenceInst(FenceInst &I);
+};
+}
+
+char FreezeAtomics::ID = 0;
+INITIALIZE_PASS(FreezeAtomics, "nacl-freeze-atomics",
+                "transform atomics, volatiles and fences into stable "
+                "@nacl.atomics.<size> intrinsics",
+                false, false)
+
+bool FreezeAtomics::runOnModule(Module &M) {
+  AtomicVisitor AV(M);
+  AV.visit(M);
+  return AV.modifiedModule();
+}
+
+NaCl::MemoryOrder AtomicVisitor::freezeMemoryOrdering(
+    llvm::AtomicOrdering AO) const {
+  // TODO For now only sequential consistency is allowed.
+  return NaCl::MemoryOrderSequentiallyConsistent;
+}
+
+bool AtomicVisitor::sizeMatchesType(const Instruction &I, unsigned S,
+                                    const Type *T) const {
+  Type *IntType(Type::getIntNTy(C, S));
+  if (IntType && T == IntType)
+    return true;
+  errs() << "Unhandled: " << I << '\n';
+  report_fatal_error("unsupported atomic size");
+}
+
+Function *AtomicVisitor::atomicIntrinsic(const Instruction &I,
+                                         unsigned AtomicBitSize) {
+  for (size_t Intr = 0; Intr != NaCl::NumAtomicIntrinsics; ++Intr)
+    if (AtomicFunctions[Intr].BitSize == AtomicBitSize)
+      return AtomicFunctions[Intr].F;
+  errs() << "Unhandled: " << I << '\n';
+  report_fatal_error("unsupported atomic bit size");
+}
+
+void AtomicVisitor::replaceWithAtomicIntrinsic(
+    Instruction &I, const Type *T, unsigned Size, NaCl::AtomicOperation O,
+    Value *Loc, Value *Val, Value *Old, AtomicOrdering AO) {
+  Value *Args[] = {
+    ConstantInt::get(Type::getInt32Ty(C), O),
+    Loc, Val, Old,
+    ConstantInt::get(Type::getInt32Ty(C), freezeMemoryOrdering(AO))
+  };
+  CallInst *Call(CallInst::Create(atomicIntrinsic(I, Size), Args, "", &I));
+  Call->setDebugLoc(I.getDebugLoc());
+  if (!I.getType()->isVoidTy())
+    I.replaceAllUsesWith(Call);
+  I.eraseFromParent();
+
+  ModifiedModule = true;
+}
+
+// %res = load {atomic|volatile} T* %ptr ordering, align sizeof(T)
+// %res = call T @nacl.atomic.<sizeof(T)>(Load, %ptr, 0, 0, ordering)
+void AtomicVisitor::visitLoadInst(LoadInst &I) {
+  if (I.isSimple())
+    return;
+  PointerHelper<LoadInst> PH(*this, I);
+  if (I.getAlignment() * 8 < PH.Size) {
+    errs() << "Unhandled: " << I << '\n';
+    report_fatal_error("atomic must be at least naturally aligned");
+  }
+  replaceWithAtomicIntrinsic(I, PH.PET, PH.Size, NaCl::AtomicLoad, PH.P,
+                             PH.Zero, PH.Zero, I.getOrdering());
+}
+
+// store {atomic|volatile} T %val, T* %ptr ordering, align sizeof(T)
+// call T @nacl.atomic.<sizeof(T)>(Store, %ptr, %val, 0, ordering)
+void AtomicVisitor::visitStoreInst(StoreInst &I) {
+  if (I.isSimple())
+    return;
+  PointerHelper<StoreInst> PH(*this, I);
+  if (I.getAlignment() * 8 < PH.Size) {
+    errs() << "Unhandled: " << I << '\n';
+    report_fatal_error("atomic must be at least naturally aligned");
+  }
+  if (!sizeMatchesType(I, PH.Size, I.getValueOperand()->getType())) {
+    errs() << "Unhandled: " << I << '\n';
+    report_fatal_error("must have integer type of the right size");
+  }
+  replaceWithAtomicIntrinsic(I, PH.PET, PH.Size, NaCl::AtomicStore, PH.P,
+                             I.getValueOperand(), PH.Zero, I.getOrdering());
+}
+
+// %res = cmpxchg T* %ptr, T %old, T %new ordering
+// %res = call T @nacl.atomic.<sizeof(T)>(CmpXchg, %ptr, %new, %old, ordering)
+void AtomicVisitor::visitAtomicCmpXchgInst(AtomicCmpXchgInst &I) {
+  PointerHelper<AtomicCmpXchgInst> PH(*this, I);
+  if (!sizeMatchesType(I, PH.Size, I.getCompareOperand()->getType()) ||
+      !sizeMatchesType(I, PH.Size, I.getNewValOperand()->getType())) {
+    errs() << "Unhandled: " << I << '\n';
+    report_fatal_error("must have integer type of the right size");
+  }
+  replaceWithAtomicIntrinsic(I, PH.PET, PH.Size, NaCl::AtomicCmpXchg, PH.P,
+                             I.getNewValOperand(), I.getCompareOperand(),
+                             I.getOrdering());
+}
+
+// %res = atomicrmw OP T* %ptr, T %val ordering
+// %res = call T @nacl.atomic.<sizeof(T)>(OP, %ptr, %val, 0, ordering)
+void AtomicVisitor::visitAtomicRMWInst(AtomicRMWInst &I) {
+  NaCl::AtomicOperation Op;
+  switch (I.getOperation()) {
+    default:
+      errs() << "Unhandled: " << I << '\n';
+      report_fatal_error("unsupported atomicrmw operation");
+    case AtomicRMWInst::Xchg: Op = NaCl::AtomicXchg; break;
+    case AtomicRMWInst::Add:  Op = NaCl::AtomicAdd;  break;
+    case AtomicRMWInst::Sub:  Op = NaCl::AtomicSub;  break;
+    case AtomicRMWInst::And:  Op = NaCl::AtomicAnd;  break;
+    case AtomicRMWInst::Or:   Op = NaCl::AtomicOr;   break;
+    case AtomicRMWInst::Xor:  Op = NaCl::AtomicXor;  break;
+  }
+  PointerHelper<AtomicRMWInst> PH(*this, I);
+  if (!sizeMatchesType(I, PH.Size, I.getValOperand()->getType())) {
+    errs() << "Unhandled: " << I << '\n';
+    report_fatal_error("must have integer type of the right size");
+  }
+  replaceWithAtomicIntrinsic(I, PH.PET, PH.Size, Op, PH.P,
+                             I.getValOperand(), PH.Zero, I.getOrdering());
+}
+
+// fence ordering
+// call i32 @nacl.atomic.<sizeof(T)>(Fence, NULL, 0, 0, ordering)
+void AtomicVisitor::visitFenceInst(FenceInst &I) {
+  Type *Int32 = Type::getInt32Ty(C);
+  Value *Zero = ConstantInt::get(Int32, 0);
+  Value *Null = ConstantPointerNull::get(PointerType::getUnqual(Int32));
+  replaceWithAtomicIntrinsic(I, Int32, 32, NaCl::AtomicFence, Null,
+                             Zero, Zero, I.getOrdering());
+}
+
+ModulePass *llvm::createFreezeAtomicsPass() {
+  return new FreezeAtomics();
+}