maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity
llvm-project/llvm/lib/CodeGen/CodePlacementOpt.cpp

359 lines
11 KiB
C++
Raw Blame History

//===-- CodePlacementOpt.cpp - Code Placement 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 optimize code placement and align loop
// headers to target specific alignment boundary.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "code-placement"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumHeaderAligned, "Number of loop header aligned");
STATISTIC(NumIntraElim, "Number of intra loop branches eliminated");
STATISTIC(NumIntraMoved, "Number of intra loop branches moved");
namespace {
class CodePlacementOpt : public MachineFunctionPass {
const MachineLoopInfo *MLI;
const TargetInstrInfo *TII;
const TargetLowering *TLI;
/// ChangedMBBs - BBs which are modified by OptimizeIntraLoopEdges.
SmallPtrSet<MachineBasicBlock*, 8> ChangedMBBs;
/// UncondJmpMBBs - A list of BBs which are in loops and end with
/// unconditional branches.
SmallVector<std::pair<MachineBasicBlock*,MachineBasicBlock*>, 4>
UncondJmpMBBs;
/// LoopHeaders - A list of BBs which are loop headers.
SmallVector<MachineBasicBlock*, 4> LoopHeaders;
public:
static char ID;
CodePlacementOpt() : MachineFunctionPass(&ID) {}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const {
return "Code Placement Optimizater";
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<MachineLoopInfo>();
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
private:
bool OptimizeIntraLoopEdges();
bool HeaderShouldBeAligned(MachineBasicBlock *MBB, MachineLoop *L,
SmallPtrSet<MachineBasicBlock*, 4> &DoNotAlign);
bool AlignLoops(MachineFunction &MF);
};
char CodePlacementOpt::ID = 0;
} // end anonymous namespace
FunctionPass *llvm::createCodePlacementOptPass() {
return new CodePlacementOpt();
}
/// OptimizeBackEdges - Place loop back edges to move unconditional branches
/// out of the loop.
///
/// A:
/// ...
/// <fallthrough to B>
///
/// B: --> loop header
/// ...
/// jcc <cond> C, [exit]
///
/// C:
/// ...
/// jmp B
///
/// ==>
///
/// A:
/// ...
/// jmp B
///
/// C:
/// ...
/// <fallthough to B>
///
/// B: --> loop header
/// ...
/// jcc <cond> C, [exit]
///
bool CodePlacementOpt::OptimizeIntraLoopEdges() {
if (!TLI->shouldOptimizeCodePlacement())
return false;
bool Changed = false;
for (unsigned i = 0, e = UncondJmpMBBs.size(); i != e; ++i) {
MachineBasicBlock *MBB = UncondJmpMBBs[i].first;
MachineBasicBlock *SuccMBB = UncondJmpMBBs[i].second;
MachineLoop *L = MLI->getLoopFor(MBB);
assert(L && "BB is expected to be in a loop!");
if (ChangedMBBs.count(MBB)) {
// BB has been modified, re-analyze.
MachineBasicBlock *TBB = 0, *FBB = 0;
SmallVector<MachineOperand, 4> Cond;
if (TII->AnalyzeBranch(*MBB, TBB, FBB, Cond) || !Cond.empty())
continue;
if (MLI->getLoopFor(TBB) != L || TBB->isLandingPad())
continue;
SuccMBB = TBB;
} else {
assert(MLI->getLoopFor(SuccMBB) == L &&
"Successor is not in the same loop!");
}
if (MBB->isLayoutSuccessor(SuccMBB)) {
// Successor is right after MBB, just eliminate the unconditional jmp.
// Can this happen?
TII->RemoveBranch(*MBB);
ChangedMBBs.insert(MBB);
++NumIntraElim;
Changed = true;
continue;
}
// Now check if the predecessor is fallthrough from any BB. If there is,
// that BB should be from outside the loop since edge will become a jmp.
bool OkToMove = true;
MachineBasicBlock *FtMBB = 0, *FtTBB = 0, *FtFBB = 0;
SmallVector<MachineOperand, 4> FtCond;
for (MachineBasicBlock::pred_iterator PI = SuccMBB->pred_begin(),
PE = SuccMBB->pred_end(); PI != PE; ++PI) {
MachineBasicBlock *PredMBB = *PI;
if (PredMBB->isLayoutSuccessor(SuccMBB)) {
if (TII->AnalyzeBranch(*PredMBB, FtTBB, FtFBB, FtCond)) {
OkToMove = false;
break;
}
if (!FtTBB)
FtTBB = SuccMBB;
else if (!FtFBB) {
assert(FtFBB != SuccMBB && "Unexpected control flow!");
FtFBB = SuccMBB;
}
// A fallthrough.
FtMBB = PredMBB;
MachineLoop *PL = MLI->getLoopFor(PredMBB);
if (PL && (PL == L || PL->getLoopDepth() >= L->getLoopDepth()))
OkToMove = false;
break;
}
}
if (!OkToMove)
continue;
// Is it profitable? If SuccMBB can fallthrough itself, that can be changed
// into a jmp.
MachineBasicBlock *TBB = 0, *FBB = 0;
SmallVector<MachineOperand, 4> Cond;
if (TII->AnalyzeBranch(*SuccMBB, TBB, FBB, Cond))
continue;
if (!TBB && Cond.empty())
TBB = next(MachineFunction::iterator(SuccMBB));
else if (!FBB && !Cond.empty())
FBB = next(MachineFunction::iterator(SuccMBB));
// This calculate the cost of the transformation. Also, it finds the *only*
// intra-loop edge if there is one.
int Cost = 0;
bool HasOneIntraSucc = true;
MachineBasicBlock *IntraSucc = 0;
for (MachineBasicBlock::succ_iterator SI = SuccMBB->succ_begin(),
SE = SuccMBB->succ_end(); SI != SE; ++SI) {
MachineBasicBlock *SSMBB = *SI;
if (MLI->getLoopFor(SSMBB) == L) {
if (!IntraSucc)
IntraSucc = SSMBB;
else
HasOneIntraSucc = false;
}
if (SuccMBB->isLayoutSuccessor(SSMBB))
// This will become a jmp.
++Cost;
else if (MBB->isLayoutSuccessor(SSMBB)) {
// One of the successor will become the new fallthrough.
if (SSMBB == FBB) {
FBB = 0;
--Cost;
} else if (!FBB && SSMBB == TBB && Cond.empty()) {
TBB = 0;
--Cost;
} else if (!Cond.empty() && !TII->ReverseBranchCondition(Cond)) {
assert(SSMBB == TBB);
TBB = FBB;
FBB = 0;
--Cost;
}
}
}
if (Cost)
continue;
// Now, let's move the successor to below the BB to eliminate the jmp.
SuccMBB->moveAfter(MBB);
TII->RemoveBranch(*MBB);
TII->RemoveBranch(*SuccMBB);
if (TBB)
TII->InsertBranch(*SuccMBB, TBB, FBB, Cond);
ChangedMBBs.insert(MBB);
ChangedMBBs.insert(SuccMBB);
if (FtMBB) {
TII->RemoveBranch(*FtMBB);
TII->InsertBranch(*FtMBB, FtTBB, FtFBB, FtCond);
ChangedMBBs.insert(FtMBB);
}
Changed = true;
// If BB is the loop latch, we may have a new loop headr.
if (MBB == L->getLoopLatch()) {
assert(MLI->isLoopHeader(SuccMBB) &&
"Only succ of loop latch is not the header?");
if (HasOneIntraSucc && IntraSucc)
std::replace(LoopHeaders.begin(),LoopHeaders.end(), SuccMBB, IntraSucc);
}
}
++NumIntraMoved;
return Changed;
}
/// HeaderShouldBeAligned - Return true if the specified loop header block
/// should be aligned. For now, we will not align it if all the predcessors
/// (i.e. loop back edges) are laid out above the header. FIXME: Do not
/// align small loops.
bool
CodePlacementOpt::HeaderShouldBeAligned(MachineBasicBlock *MBB, MachineLoop *L,
SmallPtrSet<MachineBasicBlock*, 4> &DoNotAlign) {
if (DoNotAlign.count(MBB))
return false;
bool BackEdgeBelow = false;
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
PE = MBB->pred_end(); PI != PE; ++PI) {
MachineBasicBlock *PredMBB = *PI;
if (PredMBB == MBB || PredMBB->getNumber() > MBB->getNumber()) {
BackEdgeBelow = true;
break;
}
}
if (!BackEdgeBelow)
return false;
// Ok, we are going to align this loop header. If it's an inner loop,
// do not align its outer loop.
MachineBasicBlock *PreHeader = L->getLoopPreheader();
if (PreHeader) {
MachineLoop *L = MLI->getLoopFor(PreHeader);
if (L) {
MachineBasicBlock *HeaderBlock = L->getHeader();
HeaderBlock->setAlignment(0);
DoNotAlign.insert(HeaderBlock);
}
}
return true;
}
/// AlignLoops - Align loop headers to target preferred alignments.
///
bool CodePlacementOpt::AlignLoops(MachineFunction &MF) {
const Function *F = MF.getFunction();
if (F->hasFnAttr(Attribute::OptimizeForSize))
return false;
unsigned Align = TLI->getPrefLoopAlignment();
if (!Align)
return false; // Don't care about loop alignment.
// Make sure blocks are numbered in order
MF.RenumberBlocks();
bool Changed = false;
SmallPtrSet<MachineBasicBlock*, 4> DoNotAlign;
for (unsigned i = 0, e = LoopHeaders.size(); i != e; ++i) {
MachineBasicBlock *HeaderMBB = LoopHeaders[i];
MachineBasicBlock *PredMBB = prior(MachineFunction::iterator(HeaderMBB));
MachineLoop *L = MLI->getLoopFor(HeaderMBB);
if (L == MLI->getLoopFor(PredMBB))
// If previously BB is in the same loop, don't align this BB. We want
// to prevent adding noop's inside a loop.
continue;
if (HeaderShouldBeAligned(HeaderMBB, L, DoNotAlign)) {
HeaderMBB->setAlignment(Align);
Changed = true;
++NumHeaderAligned;
}
}
return Changed;
}
bool CodePlacementOpt::runOnMachineFunction(MachineFunction &MF) {
MLI = &getAnalysis<MachineLoopInfo>();
if (MLI->empty())
return false; // No loops.
TLI = MF.getTarget().getTargetLowering();
TII = MF.getTarget().getInstrInfo();
// Analyze the BBs first and keep track of loop headers and BBs that
// end with an unconditional jmp to another block in the same loop.
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *MBB = I;
if (MBB->isLandingPad())
continue;
MachineLoop *L = MLI->getLoopFor(MBB);
if (!L)
continue;
if (MLI->isLoopHeader(MBB))
LoopHeaders.push_back(MBB);
MachineBasicBlock *TBB = 0, *FBB = 0;
SmallVector<MachineOperand, 4> Cond;
if (TII->AnalyzeBranch(*MBB, TBB, FBB, Cond) || !Cond.empty())
continue;
if (MLI->getLoopFor(TBB) == L && !TBB->isLandingPad())
UncondJmpMBBs.push_back(std::make_pair(MBB, TBB));
}
bool Changed = OptimizeIntraLoopEdges();
Changed |= AlignLoops(MF);
ChangedMBBs.clear();
UncondJmpMBBs.clear();
LoopHeaders.clear();
return Changed;
}
Reference in New Issue View Git Blame Copy Permalink