#define DEBUG_TYPE "loop-unswitch"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
+#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/Dominators.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/Support/Debug.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
#include <algorithm>
-#include <iostream>
#include <set>
using namespace llvm;
+STATISTIC(NumBranches, "Number of branches unswitched");
+STATISTIC(NumSwitches, "Number of switches unswitched");
+STATISTIC(NumSelects , "Number of selects unswitched");
+STATISTIC(NumTrivial , "Number of unswitches that are trivial");
+STATISTIC(NumSimplify, "Number of simplifications of unswitched code");
+
namespace {
- Statistic<> NumBranches("loop-unswitch", "Number of branches unswitched");
- Statistic<> NumSwitches("loop-unswitch", "Number of switches unswitched");
- Statistic<> NumSelects ("loop-unswitch", "Number of selects unswitched");
- Statistic<> NumTrivial ("loop-unswitch",
- "Number of unswitches that are trivial");
cl::opt<unsigned>
Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
cl::init(10), cl::Hidden);
- class LoopUnswitch : public FunctionPass {
+ class VISIBILITY_HIDDEN LoopUnswitch : public LoopPass {
LoopInfo *LI; // Loop information
+ LPPassManager *LPM;
+
+ // LoopProcessWorklist - Used to check if second loop needs processing
+ // after RewriteLoopBodyWithConditionConstant rewrites first loop.
+ std::vector<Loop*> LoopProcessWorklist;
+ SmallPtrSet<Value *,8> UnswitchedVals;
+
+ bool OptimizeForSize;
public:
- virtual bool runOnFunction(Function &F);
- bool visitLoop(Loop *L);
+ static char ID; // Pass ID, replacement for typeid
+ LoopUnswitch(bool Os = false) :
+ LoopPass((intptr_t)&ID), OptimizeForSize(Os) {}
+
+ bool runOnLoop(Loop *L, LPPassManager &LPM);
/// This transformation requires natural loop information & requires that
/// loop preheaders be inserted into the CFG...
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(LoopSimplifyID);
AU.addPreservedID(LoopSimplifyID);
+ AU.addPreserved<DominatorTree>();
AU.addRequired<LoopInfo>();
AU.addPreserved<LoopInfo>();
+ AU.addRequiredID(LCSSAID);
+ AU.addPreservedID(LCSSAID);
}
private:
+ /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist,
+ /// remove it.
+ void RemoveLoopFromWorklist(Loop *L) {
+ std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(),
+ LoopProcessWorklist.end(), L);
+ if (I != LoopProcessWorklist.end())
+ LoopProcessWorklist.erase(I);
+ }
+
bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L);
unsigned getLoopUnswitchCost(Loop *L, Value *LIC);
- void VersionLoop(Value *LIC, Constant *OnVal,
- Loop *L, Loop *&Out1, Loop *&Out2);
- BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To);
- void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,Constant *Val,
- bool isEqual);
- void UnswitchTrivialCondition(Loop *L, Value *Cond, bool EntersLoopOnCond,
+ void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
BasicBlock *ExitBlock);
- };
- RegisterOpt<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
-}
-
-FunctionPass *llvm::createLoopUnswitchPass() { return new LoopUnswitch(); }
-
-bool LoopUnswitch::runOnFunction(Function &F) {
- bool Changed = false;
- LI = &getAnalysis<LoopInfo>();
-
- // Transform all the top-level loops. Copy the loop list so that the child
- // can update the loop tree if it needs to delete the loop.
- std::vector<Loop*> SubLoops(LI->begin(), LI->end());
- for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
- Changed |= visitLoop(SubLoops[i]);
-
- return Changed;
-}
+ void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
+ BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To);
+ BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt);
+ void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
+ Constant *Val, bool isEqual);
-/// LoopValuesUsedOutsideLoop - Return true if there are any values defined in
-/// the loop that are used by instructions outside of it.
-static bool LoopValuesUsedOutsideLoop(Loop *L) {
- // We will be doing lots of "loop contains block" queries. Loop::contains is
- // linear time, use a set to speed this up.
- std::set<BasicBlock*> LoopBlocks;
-
- for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
- BB != E; ++BB)
- LoopBlocks.insert(*BB);
-
- for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
- BB != E; ++BB) {
- for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I)
- for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
- ++UI) {
- BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
- if (!LoopBlocks.count(UserBB))
- return true;
- }
- }
- return false;
-}
+ void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
+ BasicBlock *TrueDest,
+ BasicBlock *FalseDest,
+ Instruction *InsertPt);
-/// FindTrivialLoopExitBlock - We know that we have a branch from the loop
-/// header to the specified latch block. See if one of the successors of the
-/// latch block is an exit, and if so what block it is.
-static BasicBlock *FindTrivialLoopExitBlock(Loop *L, BasicBlock *Latch) {
- BasicBlock *Header = L->getHeader();
- BranchInst *LatchBranch = dyn_cast<BranchInst>(Latch->getTerminator());
- if (!LatchBranch || !LatchBranch->isConditional()) return 0;
-
- // Simple case, the latch block is a conditional branch. The target that
- // doesn't go to the loop header is our block if it is not in the loop.
- if (LatchBranch->getSuccessor(0) == Header) {
- if (L->contains(LatchBranch->getSuccessor(1))) return false;
- return LatchBranch->getSuccessor(1);
- } else {
- assert(LatchBranch->getSuccessor(1) == Header);
- if (L->contains(LatchBranch->getSuccessor(0))) return false;
- return LatchBranch->getSuccessor(0);
- }
+ void SimplifyCode(std::vector<Instruction*> &Worklist);
+ void RemoveBlockIfDead(BasicBlock *BB,
+ std::vector<Instruction*> &Worklist);
+ void RemoveLoopFromHierarchy(Loop *L);
+ };
+ char LoopUnswitch::ID = 0;
+ RegisterPass<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
}
-
-/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
-/// trivial: that is, that the condition controls whether or not the loop does
-/// anything at all. If this is a trivial condition, unswitching produces no
-/// code duplications (equivalently, it produces a simpler loop and a new empty
-/// loop, which gets deleted).
-///
-/// If this is a trivial condition, return ConstantBool::True if the loop body
-/// runs when the condition is true, False if the loop body executes when the
-/// condition is false. Otherwise, return null to indicate a complex condition.
-static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond,
- bool *CondEntersLoop = 0,
- BasicBlock **LoopExit = 0) {
- BasicBlock *Header = L->getHeader();
- BranchInst *HeaderTerm = dyn_cast<BranchInst>(Header->getTerminator());
-
- // If the header block doesn't end with a conditional branch on Cond, we can't
- // handle it.
- if (!HeaderTerm || !HeaderTerm->isConditional() ||
- HeaderTerm->getCondition() != Cond)
- return false;
-
- // Check to see if the conditional branch goes to the latch block. If not,
- // it's not trivial. This also determines the value of Cond that will execute
- // the loop.
- BasicBlock *Latch = L->getLoopLatch();
- if (HeaderTerm->getSuccessor(1) == Latch) {
- if (CondEntersLoop) *CondEntersLoop = true;
- } else if (HeaderTerm->getSuccessor(0) == Latch)
- if (CondEntersLoop) *CondEntersLoop = false;
- else
- return false; // Doesn't branch to latch block.
-
- // The latch block must end with a conditional branch where one edge goes to
- // the header (this much we know) and one edge goes OUT of the loop.
- BasicBlock *LoopExitBlock = FindTrivialLoopExitBlock(L, Latch);
- if (!LoopExitBlock) return 0;
- if (LoopExit) *LoopExit = LoopExitBlock;
-
- // We already know that nothing uses any scalar values defined inside of this
- // loop. As such, we just have to check to see if this loop will execute any
- // side-effecting instructions (e.g. stores, calls, volatile loads) in the
- // part of the loop that the code *would* execute.
- for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
- if (I->mayWriteToMemory())
- return false;
- for (BasicBlock::iterator I = Latch->begin(), E = Latch->end(); I != E; ++I)
- if (I->mayWriteToMemory())
- return false;
- return true;
-}
-
-/// getLoopUnswitchCost - Return the cost (code size growth) that will happen if
-/// we choose to unswitch the specified loop on the specified value.
-///
-unsigned LoopUnswitch::getLoopUnswitchCost(Loop *L, Value *LIC) {
- // If the condition is trivial, always unswitch. There is no code growth for
- // this case.
- if (IsTrivialUnswitchCondition(L, LIC))
- return 0;
-
- unsigned Cost = 0;
- // FIXME: this is brain dead. It should take into consideration code
- // shrinkage.
- for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
- I != E; ++I) {
- BasicBlock *BB = *I;
- // Do not include empty blocks in the cost calculation. This happen due to
- // loop canonicalization and will be removed.
- if (BB->begin() == BasicBlock::iterator(BB->getTerminator()))
- continue;
-
- // Count basic blocks.
- ++Cost;
- }
-
- return Cost;
+LoopPass *llvm::createLoopUnswitchPass(bool Os) {
+ return new LoopUnswitch(Os);
}
/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
// Constants should be folded, not unswitched on!
if (isa<Constant>(Cond)) return false;
-
+
// TODO: Handle: br (VARIANT|INVARIANT).
// TODO: Hoist simple expressions out of loops.
if (L->isLoopInvariant(Cond)) return Cond;
if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
return RHS;
}
-
- return 0;
+
+ return 0;
}
-bool LoopUnswitch::visitLoop(Loop *L) {
+bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
+ assert(L->isLCSSAForm());
+ LI = &getAnalysis<LoopInfo>();
+ LPM = &LPM_Ref;
bool Changed = false;
-
- // Recurse through all subloops before we process this loop. Copy the loop
- // list so that the child can update the loop tree if it needs to delete the
- // loop.
- std::vector<Loop*> SubLoops(L->begin(), L->end());
- for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
- Changed |= visitLoop(SubLoops[i]);
-
+
// Loop over all of the basic blocks in the loop. If we find an interior
// block that is branching on a loop-invariant condition, we can unswitch this
// loop.
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I) {
+ if (*I == L->getHeader())
+ continue;
TerminatorInst *TI = (*I)->getTerminator();
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
// If this isn't branching on an invariant condition, we can't unswitch
// See if this, or some part of it, is loop invariant. If so, we can
// unswitch on it if we desire.
Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed);
- if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L)) {
+ if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(),
+ L)) {
++NumBranches;
return true;
}
// Find a value to unswitch on:
// FIXME: this should chose the most expensive case!
Constant *UnswitchVal = SI->getCaseValue(1);
+ // Do not process same value again and again.
+ if (!UnswitchedVals.insert(UnswitchVal))
+ continue;
+
if (UnswitchIfProfitable(LoopCond, UnswitchVal, L)) {
++NumSwitches;
return true;
BBI != E; ++BBI)
if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
- if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L)) {
+ if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(),
+ L)) {
++NumSelects;
return true;
}
}
}
-
+
+ assert(L->isLCSSAForm());
+
return Changed;
}
+/// isTrivialLoopExitBlock - Check to see if all paths from BB either:
+/// 1. Exit the loop with no side effects.
+/// 2. Branch to the latch block with no side-effects.
+///
+/// If these conditions are true, we return true and set ExitBB to the block we
+/// exit through.
+///
+static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
+ BasicBlock *&ExitBB,
+ std::set<BasicBlock*> &Visited) {
+ if (!Visited.insert(BB).second) {
+ // Already visited and Ok, end of recursion.
+ return true;
+ } else if (!L->contains(BB)) {
+ // Otherwise, this is a loop exit, this is fine so long as this is the
+ // first exit.
+ if (ExitBB != 0) return false;
+ ExitBB = BB;
+ return true;
+ }
+
+ // Otherwise, this is an unvisited intra-loop node. Check all successors.
+ for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
+ // Check to see if the successor is a trivial loop exit.
+ if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
+ return false;
+ }
+
+ // Okay, everything after this looks good, check to make sure that this block
+ // doesn't include any side effects.
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
+ if (I->mayWriteToMemory())
+ return false;
+
+ return true;
+}
+
+/// isTrivialLoopExitBlock - Return true if the specified block unconditionally
+/// leads to an exit from the specified loop, and has no side-effects in the
+/// process. If so, return the block that is exited to, otherwise return null.
+static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
+ std::set<BasicBlock*> Visited;
+ Visited.insert(L->getHeader()); // Branches to header are ok.
+ BasicBlock *ExitBB = 0;
+ if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
+ return ExitBB;
+ return 0;
+}
+
+/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
+/// trivial: that is, that the condition controls whether or not the loop does
+/// anything at all. If this is a trivial condition, unswitching produces no
+/// code duplications (equivalently, it produces a simpler loop and a new empty
+/// loop, which gets deleted).
+///
+/// If this is a trivial condition, return true, otherwise return false. When
+/// returning true, this sets Cond and Val to the condition that controls the
+/// trivial condition: when Cond dynamically equals Val, the loop is known to
+/// exit. Finally, this sets LoopExit to the BB that the loop exits to when
+/// Cond == Val.
+///
+static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond, Constant **Val = 0,
+ BasicBlock **LoopExit = 0) {
+ BasicBlock *Header = L->getHeader();
+ TerminatorInst *HeaderTerm = Header->getTerminator();
+
+ BasicBlock *LoopExitBB = 0;
+ if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
+ // If the header block doesn't end with a conditional branch on Cond, we
+ // can't handle it.
+ if (!BI->isConditional() || BI->getCondition() != Cond)
+ return false;
+
+ // Check to see if a successor of the branch is guaranteed to go to the
+ // latch block or exit through a one exit block without having any
+ // side-effects. If so, determine the value of Cond that causes it to do
+ // this.
+ if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(0)))) {
+ if (Val) *Val = ConstantInt::getTrue();
+ } else if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(1)))) {
+ if (Val) *Val = ConstantInt::getFalse();
+ }
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
+ // If this isn't a switch on Cond, we can't handle it.
+ if (SI->getCondition() != Cond) return false;
+
+ // Check to see if a successor of the switch is guaranteed to go to the
+ // latch block or exit through a one exit block without having any
+ // side-effects. If so, determine the value of Cond that causes it to do
+ // this. Note that we can't trivially unswitch on the default case.
+ for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
+ if ((LoopExitBB = isTrivialLoopExitBlock(L, SI->getSuccessor(i)))) {
+ // Okay, we found a trivial case, remember the value that is trivial.
+ if (Val) *Val = SI->getCaseValue(i);
+ break;
+ }
+ }
+
+ // If we didn't find a single unique LoopExit block, or if the loop exit block
+ // contains phi nodes, this isn't trivial.
+ if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
+ return false; // Can't handle this.
+
+ if (LoopExit) *LoopExit = LoopExitBB;
+
+ // We already know that nothing uses any scalar values defined inside of this
+ // loop. As such, we just have to check to see if this loop will execute any
+ // side-effecting instructions (e.g. stores, calls, volatile loads) in the
+ // part of the loop that the code *would* execute. We already checked the
+ // tail, check the header now.
+ for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
+ if (I->mayWriteToMemory())
+ return false;
+ return true;
+}
+
+/// getLoopUnswitchCost - Return the cost (code size growth) that will happen if
+/// we choose to unswitch the specified loop on the specified value.
+///
+unsigned LoopUnswitch::getLoopUnswitchCost(Loop *L, Value *LIC) {
+ // If the condition is trivial, always unswitch. There is no code growth for
+ // this case.
+ if (IsTrivialUnswitchCondition(L, LIC))
+ return 0;
+
+ // FIXME: This is really overly conservative. However, more liberal
+ // estimations have thus far resulted in excessive unswitching, which is bad
+ // both in compile time and in code size. This should be replaced once
+ // someone figures out how a good estimation.
+ return L->getBlocks().size();
+
+ unsigned Cost = 0;
+ // FIXME: this is brain dead. It should take into consideration code
+ // shrinkage.
+ for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
+ I != E; ++I) {
+ BasicBlock *BB = *I;
+ // Do not include empty blocks in the cost calculation. This happen due to
+ // loop canonicalization and will be removed.
+ if (BB->begin() == BasicBlock::iterator(BB->getTerminator()))
+ continue;
+
+ // Count basic blocks.
+ ++Cost;
+ }
+
+ return Cost;
+}
+
/// UnswitchIfProfitable - We have found that we can unswitch L when
/// LoopCond == Val to simplify the loop. If we decide that this is profitable,
/// unswitch the loop, reprocess the pieces, then return true.
bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){
// Check to see if it would be profitable to unswitch this loop.
- if (getLoopUnswitchCost(L, LoopCond) > Threshold) {
+ unsigned Cost = getLoopUnswitchCost(L, LoopCond);
+
+ // Do not do non-trivial unswitch while optimizing for size.
+ if (Cost && OptimizeForSize)
+ return false;
+
+ if (Cost > Threshold) {
// FIXME: this should estimate growth by the amount of code shared by the
// resultant unswitched loops.
//
- DEBUG(std::cerr << "NOT unswitching loop %"
- << L->getHeader()->getName() << ", cost too high: "
- << L->getBlocks().size() << "\n");
+ DOUT << "NOT unswitching loop %"
+ << L->getHeader()->getName() << ", cost too high: "
+ << L->getBlocks().size() << "\n";
return false;
}
-
- // If this loop has live-out values, we can't unswitch it. We need something
- // like loop-closed SSA form in order to know how to insert PHI nodes for
- // these values.
- if (LoopValuesUsedOutsideLoop(L)) {
- DEBUG(std::cerr << "NOT unswitching loop %" << L->getHeader()->getName()
- << ", a loop value is used outside loop!\n");
- return false;
- }
-
- //std::cerr << "BEFORE:\n"; LI->dump();
- Loop *NewLoop1 = 0, *NewLoop2 = 0;
-
+
// If this is a trivial condition to unswitch (which results in no code
// duplication), do it now.
- bool EntersLoopOnCond;
+ Constant *CondVal;
BasicBlock *ExitBlock;
- if (IsTrivialUnswitchCondition(L, LoopCond, &EntersLoopOnCond, &ExitBlock)){
- UnswitchTrivialCondition(L, LoopCond, EntersLoopOnCond, ExitBlock);
- NewLoop1 = L;
+ if (IsTrivialUnswitchCondition(L, LoopCond, &CondVal, &ExitBlock)) {
+ UnswitchTrivialCondition(L, LoopCond, CondVal, ExitBlock);
} else {
- VersionLoop(LoopCond, Val, L, NewLoop1, NewLoop2);
+ UnswitchNontrivialCondition(LoopCond, Val, L);
}
-
- //std::cerr << "AFTER:\n"; LI->dump();
-
- // Try to unswitch each of our new loops now!
- if (NewLoop1) visitLoop(NewLoop1);
- if (NewLoop2) visitLoop(NewLoop2);
+
return true;
}
+/// SplitBlock - Split the specified block at the specified instruction - every
+/// thing before SplitPt stays in Old and everything starting with SplitPt moves
+/// to a new block. The two blocks are joined by an unconditional branch and
+/// the loop info is updated.
+///
+BasicBlock *LoopUnswitch::SplitBlock(BasicBlock *Old, Instruction *SplitPt) {
+ BasicBlock::iterator SplitIt = SplitPt;
+ while (isa<PHINode>(SplitIt))
+ ++SplitIt;
+ BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
+
+ // The new block lives in whichever loop the old one did.
+ if (Loop *L = LI->getLoopFor(Old))
+ L->addBasicBlockToLoop(New, *LI);
+
+ if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>())
+ DT->addNewBlock(New, Old);
+
+ return New;
+}
+
+
BasicBlock *LoopUnswitch::SplitEdge(BasicBlock *BB, BasicBlock *Succ) {
TerminatorInst *LatchTerm = BB->getTerminator();
unsigned SuccNum = 0;
// If the edge isn't critical, then BB has a single successor or Succ has a
// single pred. Split the block.
- BasicBlock *BlockToSplit;
BasicBlock::iterator SplitPoint;
if (BasicBlock *SP = Succ->getSinglePredecessor()) {
// If the successor only has a single pred, split the top of the successor
// block.
assert(SP == BB && "CFG broken");
- BlockToSplit = Succ;
- SplitPoint = Succ->begin();
+ return SplitBlock(Succ, Succ->begin());
} else {
// Otherwise, if BB has a single successor, split it at the bottom of the
// block.
assert(BB->getTerminator()->getNumSuccessors() == 1 &&
"Should have a single succ!");
- BlockToSplit = BB;
- SplitPoint = BB->getTerminator();
+ return SplitBlock(BB, BB->getTerminator());
}
-
- BasicBlock *New =
- BlockToSplit->splitBasicBlock(SplitPoint,
- BlockToSplit->getName()+".tail");
- // New now lives in whichever loop that BB used to.
- if (Loop *L = LI->getLoopFor(BlockToSplit))
- L->addBasicBlockToLoop(New, *LI);
- return New;
}
// current values into those specified by ValueMap.
//
static inline void RemapInstruction(Instruction *I,
- std::map<const Value *, Value*> &ValueMap) {
+ DenseMap<const Value *, Value*> &ValueMap) {
for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
Value *Op = I->getOperand(op);
- std::map<const Value *, Value*>::iterator It = ValueMap.find(Op);
+ DenseMap<const Value *, Value*>::iterator It = ValueMap.find(Op);
if (It != ValueMap.end()) Op = It->second;
I->setOperand(op, Op);
}
}
+// CloneDomInfo - NewBB is cloned from Orig basic block. Now clone Dominator Info.
+// If Orig is in Loop then find and use Orig dominator's cloned block as NewBB
+// dominator.
+void CloneDomInfo(BasicBlock *NewBB, BasicBlock *Orig, Loop *L,
+ DominatorTree *DT,
+ DenseMap<const Value*, Value*> &VM) {
+
+ DomTreeNode *OrigNode = DT->getNode(Orig);
+ if (!OrigNode)
+ return;
+ BasicBlock *OrigIDom = OrigNode->getBlock();
+ BasicBlock *NewIDom = OrigIDom;
+ if (L->contains(OrigIDom)) {
+ if (!DT->getNode(OrigIDom))
+ CloneDomInfo(NewIDom, OrigIDom, L, DT, VM);
+ NewIDom = cast<BasicBlock>(VM[OrigIDom]);
+ }
+ if (NewBB == NewIDom) {
+ DT->addNewBlock(NewBB, OrigIDom);
+ DT->changeImmediateDominator(NewBB, NewIDom);
+ } else
+ DT->addNewBlock(NewBB, NewIDom);
+}
+
/// CloneLoop - Recursively clone the specified loop and all of its children,
/// mapping the blocks with the specified map.
-static Loop *CloneLoop(Loop *L, Loop *PL, std::map<const Value*, Value*> &VM,
- LoopInfo *LI) {
+static Loop *CloneLoop(Loop *L, Loop *PL, DenseMap<const Value*, Value*> &VM,
+ LoopInfo *LI, LPPassManager *LPM) {
Loop *New = new Loop();
- if (PL)
- PL->addChildLoop(New);
- else
- LI->addTopLevelLoop(New);
+ LPM->insertLoop(New, PL);
// Add all of the blocks in L to the new loop.
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
// Add all of the subloops to the new loop.
for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
- CloneLoop(*I, New, VM, LI);
+ CloneLoop(*I, New, VM, LI, LPM);
return New;
}
+/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
+/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
+/// code immediately before InsertPt.
+void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
+ BasicBlock *TrueDest,
+ BasicBlock *FalseDest,
+ Instruction *InsertPt) {
+ // Insert a conditional branch on LIC to the two preheaders. The original
+ // code is the true version and the new code is the false version.
+ Value *BranchVal = LIC;
+ if (!isa<ConstantInt>(Val) || Val->getType() != Type::Int1Ty)
+ BranchVal = new ICmpInst(ICmpInst::ICMP_EQ, LIC, Val, "tmp", InsertPt);
+ else if (Val != ConstantInt::getTrue())
+ // We want to enter the new loop when the condition is true.
+ std::swap(TrueDest, FalseDest);
+
+ // Insert the new branch.
+ BranchInst *BRI = new BranchInst(TrueDest, FalseDest, BranchVal, InsertPt);
+
+ // Update dominator info.
+ if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
+ // BranchVal is a new preheader so it dominates true and false destination
+ // loop headers.
+ DT->changeImmediateDominator(TrueDest, BRI->getParent());
+ DT->changeImmediateDominator(FalseDest, BRI->getParent());
+ }
+}
+
+
/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
/// condition in it (a cond branch from its header block to its latch block,
/// where the path through the loop that doesn't execute its body has no
/// side-effects), unswitch it. This doesn't involve any code duplication, just
/// moving the conditional branch outside of the loop and updating loop info.
void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
- bool EnterOnCond,
+ Constant *Val,
BasicBlock *ExitBlock) {
- DEBUG(std::cerr << "loop-unswitch: Trivial-Unswitch loop %"
- << L->getHeader()->getName() << " [" << L->getBlocks().size()
- << " blocks] in Function " << L->getHeader()->getParent()->getName()
- << " on cond:" << *Cond << "\n");
+ DOUT << "loop-unswitch: Trivial-Unswitch loop %"
+ << L->getHeader()->getName() << " [" << L->getBlocks().size()
+ << " blocks] in Function " << L->getHeader()->getParent()->getName()
+ << " on cond: " << *Val << " == " << *Cond << "\n";
// First step, split the preheader, so that we know that there is a safe place
// to insert the conditional branch. We will change 'OrigPH' to have a
// to branch to: this is the exit block out of the loop that we should
// short-circuit to.
- // Split this edge now, so that the loop maintains its exit block.
+ // Split this block now, so that the loop maintains its exit block, and so
+ // that the jump from the preheader can execute the contents of the exit block
+ // without actually branching to it (the exit block should be dominated by the
+ // loop header, not the preheader).
assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
- BasicBlock *NewExit = SplitEdge(L->getLoopLatch(), ExitBlock);
- assert(NewExit != ExitBlock && "Edge not split!");
+ BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin());
// Okay, now we have a position to branch from and a position to branch to,
// insert the new conditional branch.
- new BranchInst(EnterOnCond ? NewPH : NewExit, EnterOnCond ? NewExit : NewPH,
- Cond, OrigPH->getTerminator());
+ EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
+ OrigPH->getTerminator());
OrigPH->getTerminator()->eraseFromParent();
+ // We need to reprocess this loop, it could be unswitched again.
+ LPM->redoLoop(L);
+
// Now that we know that the loop is never entered when this condition is a
// particular value, rewrite the loop with this info. We know that this will
// at least eliminate the old branch.
- RewriteLoopBodyWithConditionConstant(L, Cond, ConstantBool::get(EnterOnCond),
- true);
+ RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
++NumTrivial;
}
-
/// VersionLoop - We determined that the loop is profitable to unswitch when LIC
/// equal Val. Split it into loop versions and test the condition outside of
/// either loop. Return the loops created as Out1/Out2.
-void LoopUnswitch::VersionLoop(Value *LIC, Constant *Val, Loop *L,
- Loop *&Out1, Loop *&Out2) {
+void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
+ Loop *L) {
Function *F = L->getHeader()->getParent();
-
- DEBUG(std::cerr << "loop-unswitch: Unswitching loop %"
- << L->getHeader()->getName() << " [" << L->getBlocks().size()
- << " blocks] in Function " << F->getName()
- << " when '" << *Val << "' == " << *LIC << "\n");
+ DOUT << "loop-unswitch: Unswitching loop %"
+ << L->getHeader()->getName() << " [" << L->getBlocks().size()
+ << " blocks] in Function " << F->getName()
+ << " when '" << *Val << "' == " << *LIC << "\n";
// LoopBlocks contains all of the basic blocks of the loop, including the
// preheader of the loop, the body of the loop, and the exit blocks of the
LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
std::vector<BasicBlock*> ExitBlocks;
- L->getExitBlocks(ExitBlocks);
- std::sort(ExitBlocks.begin(), ExitBlocks.end());
- ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
- ExitBlocks.end());
- // Split all of the edges from inside the loop to their exit blocks. This
- // unswitching trivial: no phi nodes to update.
- unsigned NumBlocks = L->getBlocks().size();
+ L->getUniqueExitBlocks(ExitBlocks);
+
+ // Split all of the edges from inside the loop to their exit blocks. Update
+ // the appropriate Phi nodes as we do so.
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
BasicBlock *ExitBlock = ExitBlocks[i];
std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock));
for (unsigned j = 0, e = Preds.size(); j != e; ++j) {
- assert(L->contains(Preds[j]) &&
- "All preds of loop exit blocks must be the same loop!");
- SplitEdge(Preds[j], ExitBlock);
- }
+ BasicBlock* MiddleBlock = SplitEdge(Preds[j], ExitBlock);
+ BasicBlock* StartBlock = Preds[j];
+ BasicBlock* EndBlock;
+ if (MiddleBlock->getSinglePredecessor() == ExitBlock) {
+ EndBlock = MiddleBlock;
+ MiddleBlock = EndBlock->getSinglePredecessor();;
+ } else {
+ EndBlock = ExitBlock;
+ }
+
+ std::set<PHINode*> InsertedPHIs;
+ PHINode* OldLCSSA = 0;
+ for (BasicBlock::iterator I = EndBlock->begin();
+ (OldLCSSA = dyn_cast<PHINode>(I)); ++I) {
+ Value* OldValue = OldLCSSA->getIncomingValueForBlock(MiddleBlock);
+ PHINode* NewLCSSA = new PHINode(OldLCSSA->getType(),
+ OldLCSSA->getName() + ".us-lcssa",
+ MiddleBlock->getTerminator());
+ NewLCSSA->addIncoming(OldValue, StartBlock);
+ OldLCSSA->setIncomingValue(OldLCSSA->getBasicBlockIndex(MiddleBlock),
+ NewLCSSA);
+ InsertedPHIs.insert(NewLCSSA);
+ }
+
+ BasicBlock::iterator InsertPt = EndBlock->begin();
+ while (dyn_cast<PHINode>(InsertPt)) ++InsertPt;
+ for (BasicBlock::iterator I = MiddleBlock->begin();
+ (OldLCSSA = dyn_cast<PHINode>(I)) && InsertedPHIs.count(OldLCSSA) == 0;
+ ++I) {
+ PHINode *NewLCSSA = new PHINode(OldLCSSA->getType(),
+ OldLCSSA->getName() + ".us-lcssa",
+ InsertPt);
+ OldLCSSA->replaceAllUsesWith(NewLCSSA);
+ NewLCSSA->addIncoming(OldLCSSA, MiddleBlock);
+ }
+ }
}
// The exit blocks may have been changed due to edge splitting, recompute.
ExitBlocks.clear();
- L->getExitBlocks(ExitBlocks);
- std::sort(ExitBlocks.begin(), ExitBlocks.end());
- ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
- ExitBlocks.end());
-
+ L->getUniqueExitBlocks(ExitBlocks);
+
// Add exit blocks to the loop blocks.
LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
// the instructions and blocks.
std::vector<BasicBlock*> NewBlocks;
NewBlocks.reserve(LoopBlocks.size());
- std::map<const Value*, Value*> ValueMap;
+ DenseMap<const Value*, Value*> ValueMap;
for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
BasicBlock *New = CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F);
NewBlocks.push_back(New);
ValueMap[LoopBlocks[i]] = New; // Keep the BB mapping.
}
+ // Update dominator info
+ if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>())
+ for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
+ BasicBlock *LBB = LoopBlocks[i];
+ BasicBlock *NBB = NewBlocks[i];
+ CloneDomInfo(NBB, LBB, L, DT, ValueMap);
+ }
+
// Splice the newly inserted blocks into the function right before the
// original preheader.
F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(),
NewBlocks[0], F->end());
// Now we create the new Loop object for the versioned loop.
- Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI);
+ Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI, LPM);
Loop *ParentLoop = L->getParentLoop();
if (ParentLoop) {
// Make sure to add the cloned preheader and exit blocks to the parent loop
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]);
- if (ParentLoop)
- ParentLoop->addBasicBlockToLoop(cast<BasicBlock>(NewExit), *LI);
+ // The new exit block should be in the same loop as the old one.
+ if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
+ ExitBBLoop->addBasicBlockToLoop(NewExit, *LI);
assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
"Exit block should have been split to have one successor!");
for (BasicBlock::iterator I = ExitSucc->begin();
(PN = dyn_cast<PHINode>(I)); ++I) {
Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
- std::map<const Value *, Value*>::iterator It = ValueMap.find(V);
+ DenseMap<const Value *, Value*>::iterator It = ValueMap.find(V);
if (It != ValueMap.end()) V = It->second;
PN->addIncoming(V, NewExit);
}
RemapInstruction(I, ValueMap);
// Rewrite the original preheader to select between versions of the loop.
- assert(isa<BranchInst>(OrigPreheader->getTerminator()) &&
- cast<BranchInst>(OrigPreheader->getTerminator())->isUnconditional() &&
- OrigPreheader->getTerminator()->getSuccessor(0) == LoopBlocks[0] &&
+ BranchInst *OldBR = cast<BranchInst>(OrigPreheader->getTerminator());
+ assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
"Preheader splitting did not work correctly!");
- // Insert a conditional branch on LIC to the two preheaders. The original
- // code is the true version and the new code is the false version.
- Value *BranchVal = LIC;
- if (!isa<ConstantBool>(BranchVal)) {
- BranchVal = BinaryOperator::createSetEQ(LIC, Val, "tmp",
- OrigPreheader->getTerminator());
- } else if (Val != ConstantBool::True) {
- // We want to enter the new loop when the condition is true.
- BranchVal = BinaryOperator::createNot(BranchVal, "tmp",
- OrigPreheader->getTerminator());
- }
+ // Emit the new branch that selects between the two versions of this loop.
+ EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
+ OldBR->eraseFromParent();
- // Remove the unconditional branch to LoopBlocks[0] and insert the new branch.
- OrigPreheader->getInstList().pop_back();
- new BranchInst(NewBlocks[0], LoopBlocks[0], BranchVal, OrigPreheader);
+ LoopProcessWorklist.push_back(NewLoop);
+ LPM->redoLoop(L);
// Now we rewrite the original code to know that the condition is true and the
// new code to know that the condition is false.
- RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
- RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true);
- Out1 = L;
- Out2 = NewLoop;
+ RewriteLoopBodyWithConditionConstant(L , LIC, Val, false);
+
+ // It's possible that simplifying one loop could cause the other to be
+ // deleted. If so, don't simplify it.
+ if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop)
+ RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true);
+}
+
+/// RemoveFromWorklist - Remove all instances of I from the worklist vector
+/// specified.
+static void RemoveFromWorklist(Instruction *I,
+ std::vector<Instruction*> &Worklist) {
+ std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
+ Worklist.end(), I);
+ while (WI != Worklist.end()) {
+ unsigned Offset = WI-Worklist.begin();
+ Worklist.erase(WI);
+ WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
+ }
+}
+
+/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
+/// program, replacing all uses with V and update the worklist.
+static void ReplaceUsesOfWith(Instruction *I, Value *V,
+ std::vector<Instruction*> &Worklist) {
+ DOUT << "Replace with '" << *V << "': " << *I;
+
+ // Add uses to the worklist, which may be dead now.
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
+ Worklist.push_back(Use);
+
+ // Add users to the worklist which may be simplified now.
+ for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
+ UI != E; ++UI)
+ Worklist.push_back(cast<Instruction>(*UI));
+ I->replaceAllUsesWith(V);
+ I->eraseFromParent();
+ RemoveFromWorklist(I, Worklist);
+ ++NumSimplify;
}
+/// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
+/// information, and remove any dead successors it has.
+///
+void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
+ std::vector<Instruction*> &Worklist) {
+ if (pred_begin(BB) != pred_end(BB)) {
+ // This block isn't dead, since an edge to BB was just removed, see if there
+ // are any easy simplifications we can do now.
+ if (BasicBlock *Pred = BB->getSinglePredecessor()) {
+ // If it has one pred, fold phi nodes in BB.
+ while (isa<PHINode>(BB->begin()))
+ ReplaceUsesOfWith(BB->begin(),
+ cast<PHINode>(BB->begin())->getIncomingValue(0),
+ Worklist);
+
+ // If this is the header of a loop and the only pred is the latch, we now
+ // have an unreachable loop.
+ if (Loop *L = LI->getLoopFor(BB))
+ if (L->getHeader() == BB && L->contains(Pred)) {
+ // Remove the branch from the latch to the header block, this makes
+ // the header dead, which will make the latch dead (because the header
+ // dominates the latch).
+ Pred->getTerminator()->eraseFromParent();
+ new UnreachableInst(Pred);
+
+ // The loop is now broken, remove it from LI.
+ RemoveLoopFromHierarchy(L);
+
+ // Reprocess the header, which now IS dead.
+ RemoveBlockIfDead(BB, Worklist);
+ return;
+ }
+
+ // If pred ends in a uncond branch, add uncond branch to worklist so that
+ // the two blocks will get merged.
+ if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
+ if (BI->isUnconditional())
+ Worklist.push_back(BI);
+ }
+ return;
+ }
+
+ DOUT << "Nuking dead block: " << *BB;
+
+ // Remove the instructions in the basic block from the worklist.
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+ RemoveFromWorklist(I, Worklist);
+
+ // Anything that uses the instructions in this basic block should have their
+ // uses replaced with undefs.
+ if (!I->use_empty())
+ I->replaceAllUsesWith(UndefValue::get(I->getType()));
+ }
+
+ // If this is the edge to the header block for a loop, remove the loop and
+ // promote all subloops.
+ if (Loop *BBLoop = LI->getLoopFor(BB)) {
+ if (BBLoop->getLoopLatch() == BB)
+ RemoveLoopFromHierarchy(BBLoop);
+ }
+
+ // Remove the block from the loop info, which removes it from any loops it
+ // was in.
+ LI->removeBlock(BB);
+
+
+ // Remove phi node entries in successors for this block.
+ TerminatorInst *TI = BB->getTerminator();
+ std::vector<BasicBlock*> Succs;
+ for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
+ Succs.push_back(TI->getSuccessor(i));
+ TI->getSuccessor(i)->removePredecessor(BB);
+ }
+
+ // Unique the successors, remove anything with multiple uses.
+ std::sort(Succs.begin(), Succs.end());
+ Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
+
+ // Remove the basic block, including all of the instructions contained in it.
+ BB->eraseFromParent();
+
+ // Remove successor blocks here that are not dead, so that we know we only
+ // have dead blocks in this list. Nondead blocks have a way of becoming dead,
+ // then getting removed before we revisit them, which is badness.
+ //
+ for (unsigned i = 0; i != Succs.size(); ++i)
+ if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
+ // One exception is loop headers. If this block was the preheader for a
+ // loop, then we DO want to visit the loop so the loop gets deleted.
+ // We know that if the successor is a loop header, that this loop had to
+ // be the preheader: the case where this was the latch block was handled
+ // above and headers can only have two predecessors.
+ if (!LI->isLoopHeader(Succs[i])) {
+ Succs.erase(Succs.begin()+i);
+ --i;
+ }
+ }
+
+ for (unsigned i = 0, e = Succs.size(); i != e; ++i)
+ RemoveBlockIfDead(Succs[i], Worklist);
+}
+
+/// RemoveLoopFromHierarchy - We have discovered that the specified loop has
+/// become unwrapped, either because the backedge was deleted, or because the
+/// edge into the header was removed. If the edge into the header from the
+/// latch block was removed, the loop is unwrapped but subloops are still alive,
+/// so they just reparent loops. If the loops are actually dead, they will be
+/// removed later.
+void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) {
+ LPM->deleteLoopFromQueue(L);
+ RemoveLoopFromWorklist(L);
+}
+
+
+
// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
// the value specified by Val in the specified loop, or we know it does NOT have
// that value. Rewrite any uses of LIC or of properties correlated to it.
// ...
// if (li1 > li2)
// ...
-
- // NotVal - If Val is a bool, this contains its inverse.
- Constant *NotVal = 0;
- if (ConstantBool *CB = dyn_cast<ConstantBool>(Val))
- NotVal = ConstantBool::get(!CB->getValue());
// FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
// selects, switches.
std::vector<User*> Users(LIC->use_begin(), LIC->use_end());
-
- // Haha, this loop could be unswitched. Get it? The unswitch pass could
- // unswitch itself. Amazing.
- for (unsigned i = 0, e = Users.size(); i != e; ++i)
- if (Instruction *U = cast<Instruction>(Users[i]))
- if (L->contains(U->getParent()))
- if (IsEqual) {
- U->replaceUsesOfWith(LIC, Val);
- } else if (NotVal) {
- U->replaceUsesOfWith(LIC, NotVal);
- } else {
- // If we know that LIC is not Val, use this info to simplify code.
- if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) {
- for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
- if (SI->getCaseValue(i) == Val) {
- // Found a dead case value. Don't remove PHI nodes in the
- // successor if they become single-entry, those PHI nodes may
- // be in the Users list.
- SI->getSuccessor(i)->removePredecessor(SI->getParent(), true);
- SI->removeCase(i);
- break;
+ std::vector<Instruction*> Worklist;
+
+ // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
+ // in the loop with the appropriate one directly.
+ if (IsEqual || (isa<ConstantInt>(Val) && Val->getType() == Type::Int1Ty)) {
+ Value *Replacement;
+ if (IsEqual)
+ Replacement = Val;
+ else
+ Replacement = ConstantInt::get(Type::Int1Ty,
+ !cast<ConstantInt>(Val)->getZExtValue());
+
+ for (unsigned i = 0, e = Users.size(); i != e; ++i)
+ if (Instruction *U = cast<Instruction>(Users[i])) {
+ if (!L->contains(U->getParent()))
+ continue;
+ U->replaceUsesOfWith(LIC, Replacement);
+ Worklist.push_back(U);
+ }
+ } else {
+ // Otherwise, we don't know the precise value of LIC, but we do know that it
+ // is certainly NOT "Val". As such, simplify any uses in the loop that we
+ // can. This case occurs when we unswitch switch statements.
+ for (unsigned i = 0, e = Users.size(); i != e; ++i)
+ if (Instruction *U = cast<Instruction>(Users[i])) {
+ if (!L->contains(U->getParent()))
+ continue;
+
+ Worklist.push_back(U);
+
+ // If we know that LIC is not Val, use this info to simplify code.
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) {
+ for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
+ if (SI->getCaseValue(i) == Val) {
+ // Found a dead case value. Don't remove PHI nodes in the
+ // successor if they become single-entry, those PHI nodes may
+ // be in the Users list.
+
+ // FIXME: This is a hack. We need to keep the successor around
+ // and hooked up so as to preserve the loop structure, because
+ // trying to update it is complicated. So instead we preserve the
+ // loop structure and put the block on an dead code path.
+
+ BasicBlock* Old = SI->getParent();
+ BasicBlock* Split = SplitBlock(Old, SI);
+
+ Instruction* OldTerm = Old->getTerminator();
+ new BranchInst(Split, SI->getSuccessor(i),
+ ConstantInt::getTrue(), OldTerm);
+
+ Old->getTerminator()->eraseFromParent();
+
+
+ PHINode *PN;
+ for (BasicBlock::iterator II = SI->getSuccessor(i)->begin();
+ (PN = dyn_cast<PHINode>(II)); ++II) {
+ Value *InVal = PN->removeIncomingValue(Split, false);
+ PN->addIncoming(InVal, Old);
}
+
+ SI->removeCase(i);
+ break;
}
}
+ }
+
+ // TODO: We could do other simplifications, for example, turning
+ // LIC == Val -> false.
+ }
+ }
+
+ SimplifyCode(Worklist);
+}
- // TODO: We could simplify stuff like X == C.
+/// SimplifyCode - Okay, now that we have simplified some instructions in the
+/// loop, walk over it and constant prop, dce, and fold control flow where
+/// possible. Note that this is effectively a very simple loop-structure-aware
+/// optimizer. During processing of this loop, L could very well be deleted, so
+/// it must not be used.
+///
+/// FIXME: When the loop optimizer is more mature, separate this out to a new
+/// pass.
+///
+void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist) {
+ while (!Worklist.empty()) {
+ Instruction *I = Worklist.back();
+ Worklist.pop_back();
+
+ // Simple constant folding.
+ if (Constant *C = ConstantFoldInstruction(I)) {
+ ReplaceUsesOfWith(I, C, Worklist);
+ continue;
+ }
+
+ // Simple DCE.
+ if (isInstructionTriviallyDead(I)) {
+ DOUT << "Remove dead instruction '" << *I;
+
+ // Add uses to the worklist, which may be dead now.
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
+ Worklist.push_back(Use);
+ I->eraseFromParent();
+ RemoveFromWorklist(I, Worklist);
+ ++NumSimplify;
+ continue;
+ }
+
+ // Special case hacks that appear commonly in unswitched code.
+ switch (I->getOpcode()) {
+ case Instruction::Select:
+ if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(0))) {
+ ReplaceUsesOfWith(I, I->getOperand(!CB->getZExtValue()+1), Worklist);
+ continue;
+ }
+ break;
+ case Instruction::And:
+ if (isa<ConstantInt>(I->getOperand(0)) &&
+ I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS
+ cast<BinaryOperator>(I)->swapOperands();
+ if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1)))
+ if (CB->getType() == Type::Int1Ty) {
+ if (CB->isOne()) // X & 1 -> X
+ ReplaceUsesOfWith(I, I->getOperand(0), Worklist);
+ else // X & 0 -> 0
+ ReplaceUsesOfWith(I, I->getOperand(1), Worklist);
+ continue;
+ }
+ break;
+ case Instruction::Or:
+ if (isa<ConstantInt>(I->getOperand(0)) &&
+ I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS
+ cast<BinaryOperator>(I)->swapOperands();
+ if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1)))
+ if (CB->getType() == Type::Int1Ty) {
+ if (CB->isOne()) // X | 1 -> 1
+ ReplaceUsesOfWith(I, I->getOperand(1), Worklist);
+ else // X | 0 -> X
+ ReplaceUsesOfWith(I, I->getOperand(0), Worklist);
+ continue;
}
+ break;
+ case Instruction::Br: {
+ BranchInst *BI = cast<BranchInst>(I);
+ if (BI->isUnconditional()) {
+ // If BI's parent is the only pred of the successor, fold the two blocks
+ // together.
+ BasicBlock *Pred = BI->getParent();
+ BasicBlock *Succ = BI->getSuccessor(0);
+ BasicBlock *SinglePred = Succ->getSinglePredecessor();
+ if (!SinglePred) continue; // Nothing to do.
+ assert(SinglePred == Pred && "CFG broken");
+
+ DOUT << "Merging blocks: " << Pred->getName() << " <- "
+ << Succ->getName() << "\n";
+
+ // Resolve any single entry PHI nodes in Succ.
+ while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
+ ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist);
+
+ // Move all of the successor contents from Succ to Pred.
+ Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
+ Succ->end());
+ BI->eraseFromParent();
+ RemoveFromWorklist(BI, Worklist);
+
+ // If Succ has any successors with PHI nodes, update them to have
+ // entries coming from Pred instead of Succ.
+ Succ->replaceAllUsesWith(Pred);
+
+ // Remove Succ from the loop tree.
+ LI->removeBlock(Succ);
+ Succ->eraseFromParent();
+ ++NumSimplify;
+ } else if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){
+ // Conditional branch. Turn it into an unconditional branch, then
+ // remove dead blocks.
+ break; // FIXME: Enable.
+
+ DOUT << "Folded branch: " << *BI;
+ BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue());
+ BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue());
+ DeadSucc->removePredecessor(BI->getParent(), true);
+ Worklist.push_back(new BranchInst(LiveSucc, BI));
+ BI->eraseFromParent();
+ RemoveFromWorklist(BI, Worklist);
+ ++NumSimplify;
+
+ RemoveBlockIfDead(DeadSucc, Worklist);
+ }
+ break;
+ }
+ }
+ }
}
projects / oota-llvm.git / blobdiff