CGLoopInfo.cpp

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//===---- CGLoopInfo.cpp - LLVM CodeGen for loop metadata -*- C++ -*-------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "CGLoopInfo.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Metadata.h"
using namespace clang;
using namespace CodeGen;
using namespace llvm;

static MDNode *createMetadata(LLVMContext &Ctx, const LoopAttributes &Attrs) {

  if (!Attrs.IsParallel && Attrs.VectorizerWidth == 0 &&
      Attrs.VectorizerUnroll == 0 &&
      Attrs.VectorizerEnable == LoopAttributes::VecUnspecified)
    return nullptr;

  SmallVector<Value *, 4> Args;
  // Reserve operand 0 for loop id self reference.
  MDNode *TempNode = MDNode::getTemporary(Ctx, None);
  Args.push_back(TempNode);

  // Setting vectorizer.width
  if (Attrs.VectorizerWidth > 0) {
    Value *Vals[] = { MDString::get(Ctx, "llvm.loop.vectorize.width"),
                      ConstantInt::get(Type::getInt32Ty(Ctx),
                                       Attrs.VectorizerWidth) };
    Args.push_back(MDNode::get(Ctx, Vals));
  }

  // Setting vectorizer.unroll
  if (Attrs.VectorizerUnroll > 0) {
    Value *Vals[] = { MDString::get(Ctx, "llvm.loop.interleave.count"),
                      ConstantInt::get(Type::getInt32Ty(Ctx),
                                       Attrs.VectorizerUnroll) };
    Args.push_back(MDNode::get(Ctx, Vals));
  }

  // Setting vectorizer.enable
  if (Attrs.VectorizerEnable != LoopAttributes::VecUnspecified) {
    Value *Vals[] = { MDString::get(Ctx, "llvm.loop.vectorize.enable"),
                      ConstantInt::get(Type::getInt1Ty(Ctx),
                                       (Attrs.VectorizerEnable ==
                                        LoopAttributes::VecEnable)) };
    Args.push_back(MDNode::get(Ctx, Vals));
  }

  MDNode *LoopID = MDNode::get(Ctx, Args);
  assert(LoopID->use_empty() && "LoopID should not be used");

  // Set the first operand to itself.
  LoopID->replaceOperandWith(0, LoopID);
  MDNode::deleteTemporary(TempNode);
  return LoopID;
}

LoopAttributes::LoopAttributes(bool IsParallel)
    : IsParallel(IsParallel), VectorizerEnable(LoopAttributes::VecUnspecified),
      VectorizerWidth(0), VectorizerUnroll(0) {}

void LoopAttributes::clear() {
  IsParallel = false;
  VectorizerWidth = 0;
  VectorizerUnroll = 0;
  VectorizerEnable = LoopAttributes::VecUnspecified;
}

LoopInfo::LoopInfo(BasicBlock *Header, const LoopAttributes &Attrs)
    : LoopID(nullptr), Header(Header), Attrs(Attrs) {
  LoopID = createMetadata(Header->getContext(), Attrs);
}

void LoopInfoStack::push(BasicBlock *Header) {
  Active.push_back(LoopInfo(Header, StagedAttrs));
  // Clear the attributes so nested loops do not inherit them.
  StagedAttrs.clear();
}

void LoopInfoStack::pop() {
  assert(!Active.empty() && "No active loops to pop");
  Active.pop_back();
}

void LoopInfoStack::InsertHelper(Instruction *I) const {
  if (!hasInfo())
    return;

  const LoopInfo &L = getInfo();
  if (!L.getLoopID())
    return;

  if (TerminatorInst *TI = dyn_cast<TerminatorInst>(I)) {
    for (unsigned i = 0, ie = TI->getNumSuccessors(); i < ie; ++i)
      if (TI->getSuccessor(i) == L.getHeader()) {
        TI->setMetadata("llvm.loop", L.getLoopID());
        break;
      }
    return;
  }

  if (L.getAttributes().IsParallel && I->mayReadOrWriteMemory())
    I->setMetadata("llvm.mem.parallel_loop_access", L.getLoopID());
}