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https://github.com/c64scene-ar/llvm-6502.git
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766fc1db16
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84516 91177308-0d34-0410-b5e6-96231b3b80d8
318 lines
9.2 KiB
C++
318 lines
9.2 KiB
C++
//===-- CodePlacementOpt.cpp - Code Placement pass. -----------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the pass that optimize code placement and align loop
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// headers to target specific alignment boundary.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "code-placement"
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#include "llvm/CodeGen/MachineLoopInfo.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetLowering.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/Statistic.h"
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using namespace llvm;
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STATISTIC(NumLoopsAligned, "Number of loops aligned");
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STATISTIC(NumIntraElim, "Number of intra loop branches eliminated");
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STATISTIC(NumIntraMoved, "Number of intra loop branches moved");
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namespace {
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class CodePlacementOpt : public MachineFunctionPass {
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const MachineLoopInfo *MLI;
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const TargetInstrInfo *TII;
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const TargetLowering *TLI;
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/// ChangedMBBs - BBs which are modified by OptimizeIntraLoopEdges.
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SmallPtrSet<MachineBasicBlock*, 8> ChangedMBBs;
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/// UncondJmpMBBs - A list of BBs which are in loops and end with
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/// unconditional branches.
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SmallVector<std::pair<MachineBasicBlock*,MachineBasicBlock*>, 4>
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UncondJmpMBBs;
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public:
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static char ID;
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CodePlacementOpt() : MachineFunctionPass(&ID) {}
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virtual bool runOnMachineFunction(MachineFunction &MF);
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virtual const char *getPassName() const {
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return "Code Placement Optimizater";
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<MachineLoopInfo>();
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AU.addPreservedID(MachineDominatorsID);
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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private:
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bool OptimizeIntraLoopEdges();
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bool AlignLoops(MachineFunction &MF);
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bool AlignLoop(MachineFunction &MF, MachineLoop *L, unsigned Align);
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};
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char CodePlacementOpt::ID = 0;
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} // end anonymous namespace
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FunctionPass *llvm::createCodePlacementOptPass() {
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return new CodePlacementOpt();
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}
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/// OptimizeBackEdges - Place loop back edges to move unconditional branches
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/// out of the loop.
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///
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/// A:
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/// ...
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/// <fallthrough to B>
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///
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/// B: --> loop header
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/// ...
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/// jcc <cond> C, [exit]
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///
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/// C:
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/// ...
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/// jmp B
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///
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/// ==>
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///
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/// A:
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/// ...
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/// jmp B
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///
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/// C:
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/// ...
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/// <fallthough to B>
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///
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/// B: --> loop header
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/// ...
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/// jcc <cond> C, [exit]
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///
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bool CodePlacementOpt::OptimizeIntraLoopEdges() {
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if (!TLI->shouldOptimizeCodePlacement())
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return false;
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bool Changed = false;
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for (unsigned i = 0, e = UncondJmpMBBs.size(); i != e; ++i) {
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MachineBasicBlock *MBB = UncondJmpMBBs[i].first;
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MachineBasicBlock *SuccMBB = UncondJmpMBBs[i].second;
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MachineLoop *L = MLI->getLoopFor(MBB);
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assert(L && "BB is expected to be in a loop!");
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if (ChangedMBBs.count(MBB)) {
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// BB has been modified, re-analyze.
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MachineBasicBlock *TBB = 0, *FBB = 0;
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SmallVector<MachineOperand, 4> Cond;
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if (TII->AnalyzeBranch(*MBB, TBB, FBB, Cond) || !Cond.empty())
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continue;
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if (MLI->getLoopFor(TBB) != L || TBB->isLandingPad())
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continue;
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SuccMBB = TBB;
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} else {
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assert(MLI->getLoopFor(SuccMBB) == L &&
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"Successor is not in the same loop!");
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}
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if (MBB->isLayoutSuccessor(SuccMBB)) {
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// Successor is right after MBB, just eliminate the unconditional jmp.
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// Can this happen?
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TII->RemoveBranch(*MBB);
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ChangedMBBs.insert(MBB);
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++NumIntraElim;
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Changed = true;
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continue;
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}
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// Now check if the predecessor is fallthrough from any BB. If there is,
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// that BB should be from outside the loop since edge will become a jmp.
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bool OkToMove = true;
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MachineBasicBlock *FtMBB = 0, *FtTBB = 0, *FtFBB = 0;
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SmallVector<MachineOperand, 4> FtCond;
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for (MachineBasicBlock::pred_iterator PI = SuccMBB->pred_begin(),
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PE = SuccMBB->pred_end(); PI != PE; ++PI) {
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MachineBasicBlock *PredMBB = *PI;
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if (PredMBB->isLayoutSuccessor(SuccMBB)) {
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if (TII->AnalyzeBranch(*PredMBB, FtTBB, FtFBB, FtCond)) {
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OkToMove = false;
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break;
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}
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if (!FtTBB)
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FtTBB = SuccMBB;
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else if (!FtFBB) {
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assert(FtFBB != SuccMBB && "Unexpected control flow!");
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FtFBB = SuccMBB;
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}
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// A fallthrough.
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FtMBB = PredMBB;
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MachineLoop *PL = MLI->getLoopFor(PredMBB);
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if (PL && (PL == L || PL->getLoopDepth() >= L->getLoopDepth()))
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OkToMove = false;
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break;
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}
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}
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if (!OkToMove)
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continue;
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// Is it profitable? If SuccMBB can fallthrough itself, that can be changed
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// into a jmp.
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MachineBasicBlock *TBB = 0, *FBB = 0;
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SmallVector<MachineOperand, 4> Cond;
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if (TII->AnalyzeBranch(*SuccMBB, TBB, FBB, Cond))
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continue;
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if (!TBB && Cond.empty())
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TBB = next(MachineFunction::iterator(SuccMBB));
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else if (!FBB && !Cond.empty())
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FBB = next(MachineFunction::iterator(SuccMBB));
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// This calculate the cost of the transformation. Also, it finds the *only*
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// intra-loop edge if there is one.
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int Cost = 0;
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bool HasOneIntraSucc = true;
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MachineBasicBlock *IntraSucc = 0;
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for (MachineBasicBlock::succ_iterator SI = SuccMBB->succ_begin(),
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SE = SuccMBB->succ_end(); SI != SE; ++SI) {
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MachineBasicBlock *SSMBB = *SI;
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if (MLI->getLoopFor(SSMBB) == L) {
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if (!IntraSucc)
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IntraSucc = SSMBB;
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else
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HasOneIntraSucc = false;
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}
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if (SuccMBB->isLayoutSuccessor(SSMBB))
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// This will become a jmp.
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++Cost;
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else if (MBB->isLayoutSuccessor(SSMBB)) {
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// One of the successor will become the new fallthrough.
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if (SSMBB == FBB) {
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FBB = 0;
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--Cost;
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} else if (!FBB && SSMBB == TBB && Cond.empty()) {
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TBB = 0;
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--Cost;
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} else if (!Cond.empty() && !TII->ReverseBranchCondition(Cond)) {
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assert(SSMBB == TBB);
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TBB = FBB;
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FBB = 0;
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--Cost;
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}
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}
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}
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if (Cost)
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continue;
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// Now, let's move the successor to below the BB to eliminate the jmp.
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SuccMBB->moveAfter(MBB);
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TII->RemoveBranch(*MBB);
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TII->RemoveBranch(*SuccMBB);
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if (TBB)
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TII->InsertBranch(*SuccMBB, TBB, FBB, Cond);
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ChangedMBBs.insert(MBB);
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ChangedMBBs.insert(SuccMBB);
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if (FtMBB) {
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TII->RemoveBranch(*FtMBB);
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TII->InsertBranch(*FtMBB, FtTBB, FtFBB, FtCond);
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ChangedMBBs.insert(FtMBB);
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}
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Changed = true;
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}
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++NumIntraMoved;
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return Changed;
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}
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/// AlignLoops - Align loop headers to target preferred alignments.
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///
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bool CodePlacementOpt::AlignLoops(MachineFunction &MF) {
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const Function *F = MF.getFunction();
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if (F->hasFnAttr(Attribute::OptimizeForSize))
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return false;
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unsigned Align = TLI->getPrefLoopAlignment();
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if (!Align)
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return false; // Don't care about loop alignment.
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bool Changed = false;
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for (MachineLoopInfo::iterator I = MLI->begin(), E = MLI->end();
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I != E; ++I)
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Changed |= AlignLoop(MF, *I, Align);
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return Changed;
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}
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bool CodePlacementOpt::AlignLoop(MachineFunction &MF, MachineLoop *L,
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unsigned Align) {
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bool Changed = false;
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// Do alignment for nested loops.
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for (MachineLoop::iterator I = L->begin(), E = L->end(); I != E; ++I)
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Changed |= AlignLoop(MF, *I, Align);
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MachineBasicBlock *TopMBB = L->getHeader();
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if (TopMBB == MF.begin()) return Changed;
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MachineBasicBlock *PredMBB = prior(MachineFunction::iterator(TopMBB));
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while (MLI->getLoopFor(PredMBB) == L) {
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TopMBB = PredMBB;
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if (TopMBB == MF.begin()) return Changed;
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PredMBB = prior(MachineFunction::iterator(TopMBB));
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}
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TopMBB->setAlignment(Align);
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Changed = true;
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++NumLoopsAligned;
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return Changed;
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}
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bool CodePlacementOpt::runOnMachineFunction(MachineFunction &MF) {
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MLI = &getAnalysis<MachineLoopInfo>();
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if (MLI->empty())
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return false; // No loops.
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TLI = MF.getTarget().getTargetLowering();
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TII = MF.getTarget().getInstrInfo();
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// Analyze the BBs first and keep track of BBs that
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// end with an unconditional jmp to another block in the same loop.
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for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
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MachineBasicBlock *MBB = I;
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if (MBB->isLandingPad())
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continue;
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MachineLoop *L = MLI->getLoopFor(MBB);
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if (!L)
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continue;
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MachineBasicBlock *TBB = 0, *FBB = 0;
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SmallVector<MachineOperand, 4> Cond;
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if (TII->AnalyzeBranch(*MBB, TBB, FBB, Cond) || !Cond.empty())
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continue;
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if (MLI->getLoopFor(TBB) == L && !TBB->isLandingPad())
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UncondJmpMBBs.push_back(std::make_pair(MBB, TBB));
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}
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bool Changed = OptimizeIntraLoopEdges();
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Changed |= AlignLoops(MF);
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ChangedMBBs.clear();
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UncondJmpMBBs.clear();
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return Changed;
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}
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