PNaCl: Add support for GCC/LLVM vector extensions

lib/Transforms/NaCl/FixVectorLoadStoreAlignment.cpp

+//===- FixVectorLoadStoreAlignment.cpp - Vector load/store alignment ------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Replace all vector load/store instructions by loads/stores of each
+// individual element since different architectures have different
+// faults on unaligned memory access. This pass pessimizes all vector
+// memory accesses. It's expected that backends with more liberal
+// alignment restrictions recognize this pattern and reconstruct the
+// original vector load/store.
+//
+// Volatile load/store are broken up as allowed by C/C++, and atomic
+// accesses cause errors at compile-time.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Transforms/NaCl.h"
+
+using namespace llvm;
+
+namespace {
+class FixVectorLoadStoreAlignment : public BasicBlockPass {
+public:
+  static char ID; // Pass identification, replacement for typeid
+  FixVectorLoadStoreAlignment() : BasicBlockPass(ID), M(0), DL(0) {
+    initializeFixVectorLoadStoreAlignmentPass(*PassRegistry::getPassRegistry());
+  }
+  virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+    AU.addRequired<DataLayout>();
+    BasicBlockPass::getAnalysisUsage(AU);
+  }
+  virtual bool doInitialization(Module &Mod) {
+    M = &Mod;
+    return false; // Unchanged.
+  }
+  virtual bool runOnBasicBlock(BasicBlock &BB);
+
+private:
+  typedef SmallVector<Instruction *, 8> Instructions;
+  const Module *M;
+  const DataLayout *DL;
+
+  /// Some sub-classes of Instruction have a non-virtual function
+  /// indicating which operand is the pointer operand. This template
+  /// function returns the pointer operand's type, and requires that
+  /// InstTy have a getPointerOperand function.
+  template <typename InstTy>
+  static PointerType *pointerOperandType(const InstTy *I) {
+    return cast<PointerType>(I->getPointerOperand()->getType());
+  }
+
+  /// Similar to pointerOperandType, this template function checks
+  /// whether the pointer operand is a pointer to a vector type.
+  template <typename InstTy>
+  static bool pointerOperandIsVectorPointer(const Instruction *I) {
+    return pointerOperandType(cast<InstTy>(I))->getElementType()->isVectorTy();
+  }
+
+  /// Returns true if one of the Instruction's operands is a pointer to
+  /// a vector type. This is more general than the above and assumes we
+  /// don't know which Instruction type is provided.
+  static bool hasVectorPointerOperand(const Instruction *I) {
+    for (User::const_op_iterator IB = I->op_begin(), IE = I->op_end(); IB != IE;
+         ++IB)
+      if (PointerType *PtrTy = dyn_cast<PointerType>((*IB)->getType()))
+        if (isa<VectorType>(PtrTy->getElementType()))
+          return true;
+    return false;
+  }
+
+  void findVectorLoadStore(const BasicBlock &BB, Instructions &Loads,
+                           Instructions &Stores) const;
+  void fixVectorLoadStoreAlignment(BasicBlock &BB, const Instructions &Loads,
+                                   const Instructions &Stores) const;
+};
+} // anonymous namespace
+
+char FixVectorLoadStoreAlignment::ID = 0;
+INITIALIZE_PASS(FixVectorLoadStoreAlignment, "fix-vector-load-store-alignment",
+                "Replace vector load/store by loads/stores of each element",
+                false, false)
+
+void FixVectorLoadStoreAlignment::findVectorLoadStore(
+    const BasicBlock &BB, Instructions &Loads, Instructions &Stores) const {
+  for (BasicBlock::const_iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE;
+       ++BBI) {
+    Instruction *I = const_cast<Instruction *>(&*BBI);
+    // The following list of instructions is based on mayReadOrWriteMemory.
+    switch (I->getOpcode()) {
+    case Instruction::Load:
+      if (pointerOperandIsVectorPointer<LoadInst>(I)) {
+        if (cast<LoadInst>(I)->isAtomic())
+          report_fatal_error("unhandled: atomic vector store");
+        Loads.push_back(I);
+      }
+      break;
+    case Instruction::Store:
+      if (pointerOperandIsVectorPointer<StoreInst>(I)) {
+        if (cast<StoreInst>(I)->isAtomic())
+          report_fatal_error("unhandled: atomic vector store");
+        Stores.push_back(I);
+      }
+      break;
+    case Instruction::Alloca:
+    case Instruction::Fence:
+    case Instruction::VAArg:
+      // Leave these memory operations as-is, even when they deal with
+      // vectors.
+      break;
+    case Instruction::Call:
+    case Instruction::Invoke:
+      // Call/invoke don't touch memory per-se, leave them as-is.
+      break;
+    case Instruction::AtomicCmpXchg:
+      if (pointerOperandIsVectorPointer<AtomicCmpXchgInst>(I))
+        report_fatal_error(
+            "unhandled: atomic compare and exchange operation on vector");
+      break;
+    case Instruction::AtomicRMW:
+      if (pointerOperandIsVectorPointer<AtomicRMWInst>(I))
+        report_fatal_error("unhandled: atomic RMW operation on vector");
+      break;
+    default:
+      if (I->mayReadOrWriteMemory() && hasVectorPointerOperand(I)) {
+        errs() << "Not handled: " << *I << '\n';
+        report_fatal_error(
+            "unexpected: vector operations which may read/write memory");
+      }
+      break;
+    }
+  }
+}
+
+void FixVectorLoadStoreAlignment::fixVectorLoadStoreAlignment(
+    BasicBlock &BB, const Instructions &Loads,
+    const Instructions &Stores) const {
+  for (Instructions::const_iterator IB = Loads.begin(), IE = Loads.end();
+       IB != IE; ++IB) {
+    LoadInst *VecLoad = cast<LoadInst>(*IB);
+    VectorType *LoadedVecTy =
+        cast<VectorType>(pointerOperandType(VecLoad)->getElementType());
+    Type *ElemTy = LoadedVecTy->getElementType();
+
+    // The base of the vector is as aligned as the vector load (where
+    // zero means ABI alignment for the vector), whereas subsequent
+    // elements are as aligned as the base+offset can be.
+    unsigned BaseAlign = VecLoad->getAlignment()
+                             ? VecLoad->getAlignment()
+                             : DL->getABITypeAlignment(LoadedVecTy);
+    unsigned ElemAllocSize = DL->getTypeAllocSize(ElemTy);
+
+    // Fill in the vector element by element.
+    IRBuilder<> IRB(VecLoad);
+    Value *Loaded = UndefValue::get(LoadedVecTy);
+    Value *Base =
+        IRB.CreateBitCast(VecLoad->getPointerOperand(), ElemTy->getPointerTo());
+
+    for (unsigned Elem = 0, NumElems = LoadedVecTy->getNumElements();
+         Elem != NumElems; ++Elem) {
+      unsigned Align = MinAlign(BaseAlign, ElemAllocSize * Elem);
+      Value *GEP = IRB.CreateConstInBoundsGEP1_32(Base, Elem);
+      LoadInst *LoadedElem =
+          IRB.CreateAlignedLoad(GEP, Align, VecLoad->isVolatile());
+      LoadedElem->setSynchScope(VecLoad->getSynchScope());
+      Loaded = IRB.CreateInsertElement(
+          Loaded, LoadedElem,
+          ConstantInt::get(Type::getInt32Ty(M->getContext()), Elem));
+    }
+
+    VecLoad->replaceAllUsesWith(Loaded);
+    VecLoad->eraseFromParent();
+  }
+
+  for (Instructions::const_iterator IB = Stores.begin(), IE = Stores.end();
+       IB != IE; ++IB) {
+    StoreInst *VecStore = cast<StoreInst>(*IB);
+    Value *StoredVec = VecStore->getValueOperand();
+    VectorType *StoredVecTy = cast<VectorType>(StoredVec->getType());
+    Type *ElemTy = StoredVecTy->getElementType();
+
+    unsigned BaseAlign = VecStore->getAlignment()
+                             ? VecStore->getAlignment()
+                             : DL->getABITypeAlignment(StoredVecTy);
+    unsigned ElemAllocSize = DL->getTypeAllocSize(ElemTy);
+
+    // Fill in the vector element by element.
+    IRBuilder<> IRB(VecStore);
+    Value *Base = IRB.CreateBitCast(VecStore->getPointerOperand(),
+                                    ElemTy->getPointerTo());
+
+    for (unsigned Elem = 0, NumElems = StoredVecTy->getNumElements();
+         Elem != NumElems; ++Elem) {
+      unsigned Align = MinAlign(BaseAlign, ElemAllocSize * Elem);
+      Value *GEP = IRB.CreateConstInBoundsGEP1_32(Base, Elem);
+      Value *ElemToStore = IRB.CreateExtractElement(
+          StoredVec, ConstantInt::get(Type::getInt32Ty(M->getContext()), Elem));
+      StoreInst *StoredElem = IRB.CreateAlignedStore(ElemToStore, GEP, Align,
+                                                     VecStore->isVolatile());

[jvoung (off chromium), 2014/04/16 22:03:12]

Can add a test case that shows volatile is propagated to the scalar load/stores
by the pass.

[JF, 2014/04/16 22:35:36]

Done.

+      StoredElem->setSynchScope(VecStore->getSynchScope());
+    }
+
+    VecStore->eraseFromParent();
+  }
+}
+
+bool FixVectorLoadStoreAlignment::runOnBasicBlock(BasicBlock &BB) {
+  bool Changed = false;
+  if (!DL)
+    DL = &getAnalysis<DataLayout>();
+  Instructions Loads;
+  Instructions Stores;
+  findVectorLoadStore(BB, Loads, Stores);
+  if (!(Loads.empty() && Stores.empty())) {
+    Changed = true;
+    fixVectorLoadStoreAlignment(BB, Loads, Stores);
+  }
+  return Changed;
+}
+
+BasicBlockPass *llvm::createFixVectorLoadStoreAlignmentPass() {
+  return new FixVectorLoadStoreAlignment();
+}