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//===-- LoopAligner.cpp - Loop aligner pass. ------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the pass that align loop headers to target specific
// alignment boundary.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loopalign"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
namespace {
class LoopAligner : public MachineFunctionPass {
public:
static char ID;
LoopAligner() : MachineFunctionPass(&ID) {}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const { return "Loop aligner"; }
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<MachineLoopInfo>();
AU.addPreserved<MachineLoopInfo>();
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
};
char LoopAligner::ID = 0;
} // end anonymous namespace
FunctionPass *llvm::createLoopAlignerPass() { return new LoopAligner(); }
bool LoopAligner::runOnMachineFunction(MachineFunction &MF) {
const MachineLoopInfo *MLI = &getAnalysis<MachineLoopInfo>();
if (MLI->empty())
return false; // No loops.
const TargetLowering *TLI = MF.getTarget().getTargetLowering();
if (!TLI)
return false;
unsigned Align = TLI->getPrefLoopAlignment();
if (!Align)
return false; // Don't care about loop alignment.
const Function *F = MF.getFunction();
if (F->hasFnAttr(Attribute::OptimizeForSize))
return false;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *MBB = I;
if (MLI->isLoopHeader(MBB)) {
MachineBasicBlock *PredBB = prior(I);
if (MLI->getLoopFor(MBB) == MLI->getLoopFor(PredBB))
// If previously BB is in the same loop, don't align this BB. We want
// to prevent adding noop's inside a loop.
continue;
MBB->setAlignment(Align);
}
}
return true;
}
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