lib/CodeGen/LoopAligner.cpp

   1 //===-- LoopAligner.cpp - Loop aligner pass. ------------------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements the pass that align loop headers to target specific
  11 // alignment boundary.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #define DEBUG_TYPE "loopalign"
  16 #include "llvm/CodeGen/MachineLoopInfo.h"
  17 #include "llvm/CodeGen/MachineFunctionPass.h"
  18 #include "llvm/CodeGen/Passes.h"
  19 #include "llvm/Target/TargetLowering.h"
  20 #include "llvm/Target/TargetMachine.h"
  21 #include "llvm/Support/Compiler.h"
  22 #include "llvm/Support/Debug.h"
  23 using namespace llvm;
  24
  25 namespace {
  26   class LoopAligner : public MachineFunctionPass {
  27   public:
  28     static char ID;
  29     LoopAligner() : MachineFunctionPass(&ID) {}
  30
  31     virtual bool runOnMachineFunction(MachineFunction &MF);
  32     virtual const char *getPassName() const { return "Loop aligner"; }
  33
  34     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  35       AU.addRequired<MachineLoopInfo>();
  36       AU.addPreserved<MachineLoopInfo>();
  37       AU.addPreservedID(MachineDominatorsID);
  38       MachineFunctionPass::getAnalysisUsage(AU);
  39     }
  40   };
  41
  42   char LoopAligner::ID = 0;
  43 } // end anonymous namespace
  44
  45 FunctionPass *llvm::createLoopAlignerPass() { return new LoopAligner(); }
  46
  47 bool LoopAligner::runOnMachineFunction(MachineFunction &MF) {
  48   const MachineLoopInfo *MLI = &getAnalysis<MachineLoopInfo>();
  49
  50   if (MLI->empty())
  51     return false;  // No loops.
  52
  53   const TargetLowering *TLI = MF.getTarget().getTargetLowering();
  54   if (!TLI)
  55     return false;
  56
  57   unsigned Align = TLI->getPrefLoopAlignment();
  58   if (!Align)
  59     return false;  // Don't care about loop alignment.
  60
  61   const Function *F = MF.getFunction();
  62   if (F->hasFnAttr(Attribute::OptimizeForSize))
  63     return false;
  64
  65   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
  66     MachineBasicBlock *MBB = I;
  67     if (MLI->isLoopHeader(MBB)) {
  68       MachineBasicBlock *PredBB = prior(I);
  69       if (MLI->getLoopFor(MBB) == MLI->getLoopFor(PredBB))
  70         // If previously BB is in the same loop, don't align this BB. We want
  71         // to prevent adding noop's inside a loop.
  72         continue;
  73       MBB->setAlignment(Align);
  74     }
  75   }
  76
  77   return true;
  78 }