//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "loop-rotate"
#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AssumptionTracker.h"
#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
-#include "llvm/Function.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/Support/CFG.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
using namespace llvm;
-#define MAX_HEADER_SIZE 16
+#define DEBUG_TYPE "loop-rotate"
+
+static cl::opt<unsigned>
+DefaultRotationThreshold("rotation-max-header-size", cl::init(16), cl::Hidden,
+ cl::desc("The default maximum header size for automatic loop rotation"));
STATISTIC(NumRotated, "Number of loops rotated");
namespace {
class LoopRotate : public LoopPass {
public:
static char ID; // Pass ID, replacement for typeid
- LoopRotate() : LoopPass(ID) {
+ LoopRotate(int SpecifiedMaxHeaderSize = -1) : LoopPass(ID) {
initializeLoopRotatePass(*PassRegistry::getPassRegistry());
+ if (SpecifiedMaxHeaderSize == -1)
+ MaxHeaderSize = DefaultRotationThreshold;
+ else
+ MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
}
// LCSSA form makes instruction renaming easier.
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addPreserved<DominatorTree>();
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<AssumptionTracker>();
+ AU.addPreserved<DominatorTreeWrapperPass>();
AU.addRequired<LoopInfo>();
AU.addPreserved<LoopInfo>();
AU.addRequiredID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addPreservedID(LCSSAID);
AU.addPreserved<ScalarEvolution>();
+ AU.addRequired<TargetTransformInfo>();
}
- bool runOnLoop(Loop *L, LPPassManager &LPM);
- void simplifyLoopLatch(Loop *L);
- bool rotateLoop(Loop *L);
+ bool runOnLoop(Loop *L, LPPassManager &LPM) override;
+ bool simplifyLoopLatch(Loop *L);
+ bool rotateLoop(Loop *L, bool SimplifiedLatch);
private:
+ unsigned MaxHeaderSize;
LoopInfo *LI;
+ const TargetTransformInfo *TTI;
+ AssumptionTracker *AT;
};
}
char LoopRotate::ID = 0;
INITIALIZE_PASS_BEGIN(LoopRotate, "loop-rotate", "Rotate Loops", false, false)
+INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
+INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_DEPENDENCY(LCSSA)
INITIALIZE_PASS_END(LoopRotate, "loop-rotate", "Rotate Loops", false, false)
-Pass *llvm::createLoopRotatePass() { return new LoopRotate(); }
+Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {
+ return new LoopRotate(MaxHeaderSize);
+}
/// Rotate Loop L as many times as possible. Return true if
/// the loop is rotated at least once.
bool LoopRotate::runOnLoop(Loop *L, LPPassManager &LPM) {
+ if (skipOptnoneFunction(L))
+ return false;
+
+ // Save the loop metadata.
+ MDNode *LoopMD = L->getLoopID();
+
LI = &getAnalysis<LoopInfo>();
+ TTI = &getAnalysis<TargetTransformInfo>();
+ AT = &getAnalysis<AssumptionTracker>();
// Simplify the loop latch before attempting to rotate the header
// upward. Rotation may not be needed if the loop tail can be folded into the
// loop exit.
- simplifyLoopLatch(L);
+ bool SimplifiedLatch = simplifyLoopLatch(L);
// One loop can be rotated multiple times.
bool MadeChange = false;
- while (rotateLoop(L))
+ while (rotateLoop(L, SimplifiedLatch)) {
MadeChange = true;
+ SimplifiedLatch = false;
+ }
+
+ // Restore the loop metadata.
+ // NB! We presume LoopRotation DOESN'T ADD its own metadata.
+ if ((MadeChange || SimplifiedLatch) && LoopMD)
+ L->setLoopID(LoopMD);
return MadeChange;
}
for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
UE = OrigHeaderVal->use_end(); UI != UE; ) {
// Grab the use before incrementing the iterator.
- Use &U = UI.getUse();
+ Use &U = *UI;
// Increment the iterator before removing the use from the list.
++UI;
}
}
-/// Determine whether the instructions in this range my be safely and cheaply
+/// Determine whether the instructions in this range may be safely and cheaply
/// speculated. This is not an important enough situation to develop complex
/// heuristics. We handle a single arithmetic instruction along with any type
/// conversions.
/// Fold the loop tail into the loop exit by speculating the loop tail
/// instructions. Typically, this is a single post-increment. In the case of a
/// simple 2-block loop, hoisting the increment can be much better than
-/// duplicating the entire loop header. In the cast of loops with early exits,
+/// duplicating the entire loop header. In the case of loops with early exits,
/// rotation will not work anyway, but simplifyLoopLatch will put the loop in
/// canonical form so downstream passes can handle it.
///
/// I don't believe this invalidates SCEV.
-void LoopRotate::simplifyLoopLatch(Loop *L) {
+bool LoopRotate::simplifyLoopLatch(Loop *L) {
BasicBlock *Latch = L->getLoopLatch();
if (!Latch || Latch->hasAddressTaken())
- return;
+ return false;
BranchInst *Jmp = dyn_cast<BranchInst>(Latch->getTerminator());
if (!Jmp || !Jmp->isUnconditional())
- return;
+ return false;
BasicBlock *LastExit = Latch->getSinglePredecessor();
if (!LastExit || !L->isLoopExiting(LastExit))
- return;
+ return false;
BranchInst *BI = dyn_cast<BranchInst>(LastExit->getTerminator());
if (!BI)
- return;
+ return false;
if (!shouldSpeculateInstrs(Latch->begin(), Jmp))
- return;
+ return false;
DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into "
<< LastExit->getName() << "\n");
// Nuke the Latch block.
assert(Latch->empty() && "unable to evacuate Latch");
LI->removeBlock(Latch);
- if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>())
- DT->eraseNode(Latch);
+ if (DominatorTreeWrapperPass *DTWP =
+ getAnalysisIfAvailable<DominatorTreeWrapperPass>())
+ DTWP->getDomTree().eraseNode(Latch);
Latch->eraseFromParent();
+ return true;
}
/// Rotate loop LP. Return true if the loop is rotated.
-bool LoopRotate::rotateLoop(Loop *L) {
+///
+/// \param SimplifiedLatch is true if the latch was just folded into the final
+/// loop exit. In this case we may want to rotate even though the new latch is
+/// now an exiting branch. This rotation would have happened had the latch not
+/// been simplified. However, if SimplifiedLatch is false, then we avoid
+/// rotating loops in which the latch exits to avoid excessive or endless
+/// rotation. LoopRotate should be repeatable and converge to a canonical
+/// form. This property is satisfied because simplifying the loop latch can only
+/// happen once across multiple invocations of the LoopRotate pass.
+bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
// If the loop has only one block then there is not much to rotate.
if (L->getBlocks().size() == 1)
return false;
BasicBlock *OrigLatch = L->getLoopLatch();
BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
- if (BI == 0 || BI->isUnconditional())
+ if (!BI || BI->isUnconditional())
return false;
// If the loop header is not one of the loop exiting blocks then
// If the loop latch already contains a branch that leaves the loop then the
// loop is already rotated.
- if (OrigLatch == 0 || L->isLoopExiting(OrigLatch))
+ if (!OrigLatch)
+ return false;
+
+ // Rotate if either the loop latch does *not* exit the loop, or if the loop
+ // latch was just simplified.
+ if (L->isLoopExiting(OrigLatch) && !SimplifiedLatch)
return false;
- // Check size of original header and reject loop if it is very big.
+ // Check size of original header and reject loop if it is very big or we can't
+ // duplicate blocks inside it.
{
+ SmallPtrSet<const Value *, 32> EphValues;
+ CodeMetrics::collectEphemeralValues(L, AT, EphValues);
+
CodeMetrics Metrics;
- Metrics.analyzeBasicBlock(OrigHeader);
- if (Metrics.NumInsts > MAX_HEADER_SIZE)
+ Metrics.analyzeBasicBlock(OrigHeader, *TTI, EphValues);
+ if (Metrics.notDuplicatable) {
+ DEBUG(dbgs() << "LoopRotation: NOT rotating - contains non-duplicatable"
+ << " instructions: "; L->dump());
+ return false;
+ }
+ if (Metrics.NumInsts > MaxHeaderSize)
return false;
}
// If the loop could not be converted to canonical form, it must have an
// indirectbr in it, just give up.
- if (OrigPreheader == 0)
+ if (!OrigPreheader)
return false;
// Anything ScalarEvolution may know about this loop or the PHI nodes
// With the operands remapped, see if the instruction constant folds or is
// otherwise simplifyable. This commonly occurs because the entry from PHI
// nodes allows icmps and other instructions to fold.
+ // FIXME: Provide DL, TLI, DT, AT to SimplifyInstruction.
Value *V = SimplifyInstruction(C);
if (V && LI->replacementPreservesLCSSAForm(C, V)) {
// If so, then delete the temporary instruction and stick the folded value
// The conditional branch can't be folded, handle the general case.
// Update DominatorTree to reflect the CFG change we just made. Then split
// edges as necessary to preserve LoopSimplify form.
- if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) {
+ if (DominatorTreeWrapperPass *DTWP =
+ getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
+ DominatorTree &DT = DTWP->getDomTree();
// Everything that was dominated by the old loop header is now dominated
// by the original loop preheader. Conceptually the header was merged
// into the preheader, even though we reuse the actual block as a new
// loop latch.
- DomTreeNode *OrigHeaderNode = DT->getNode(OrigHeader);
+ DomTreeNode *OrigHeaderNode = DT.getNode(OrigHeader);
SmallVector<DomTreeNode *, 8> HeaderChildren(OrigHeaderNode->begin(),
OrigHeaderNode->end());
- DomTreeNode *OrigPreheaderNode = DT->getNode(OrigPreheader);
+ DomTreeNode *OrigPreheaderNode = DT.getNode(OrigPreheader);
for (unsigned I = 0, E = HeaderChildren.size(); I != E; ++I)
- DT->changeImmediateDominator(HeaderChildren[I], OrigPreheaderNode);
+ DT.changeImmediateDominator(HeaderChildren[I], OrigPreheaderNode);
- assert(DT->getNode(Exit)->getIDom() == OrigPreheaderNode);
- assert(DT->getNode(NewHeader)->getIDom() == OrigPreheaderNode);
+ assert(DT.getNode(Exit)->getIDom() == OrigPreheaderNode);
+ assert(DT.getNode(NewHeader)->getIDom() == OrigPreheaderNode);
// Update OrigHeader to be dominated by the new header block.
- DT->changeImmediateDominator(OrigHeader, OrigLatch);
+ DT.changeImmediateDominator(OrigHeader, OrigLatch);
}
// Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
NewPH->setName(NewHeader->getName() + ".lr.ph");
// Preserve canonical loop form, which means that 'Exit' should have only
- // one predecessor.
- BasicBlock *ExitSplit = SplitCriticalEdge(L->getLoopLatch(), Exit, this);
- ExitSplit->moveBefore(Exit);
+ // one predecessor. Note that Exit could be an exit block for multiple
+ // nested loops, causing both of the edges to now be critical and need to
+ // be split.
+ SmallVector<BasicBlock *, 4> ExitPreds(pred_begin(Exit), pred_end(Exit));
+ bool SplitLatchEdge = false;
+ for (SmallVectorImpl<BasicBlock *>::iterator PI = ExitPreds.begin(),
+ PE = ExitPreds.end();
+ PI != PE; ++PI) {
+ // We only need to split loop exit edges.
+ Loop *PredLoop = LI->getLoopFor(*PI);
+ if (!PredLoop || PredLoop->contains(Exit))
+ continue;
+ SplitLatchEdge |= L->getLoopLatch() == *PI;
+ BasicBlock *ExitSplit = SplitCriticalEdge(*PI, Exit, this);
+ ExitSplit->moveBefore(Exit);
+ }
+ assert(SplitLatchEdge &&
+ "Despite splitting all preds, failed to split latch exit?");
} else {
// We can fold the conditional branch in the preheader, this makes things
// simpler. The first step is to remove the extra edge to the Exit block.
PHBI->eraseFromParent();
// With our CFG finalized, update DomTree if it is available.
- if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) {
+ if (DominatorTreeWrapperPass *DTWP =
+ getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
+ DominatorTree &DT = DTWP->getDomTree();
// Update OrigHeader to be dominated by the new header block.
- DT->changeImmediateDominator(NewHeader, OrigPreheader);
- DT->changeImmediateDominator(OrigHeader, OrigLatch);
+ DT.changeImmediateDominator(NewHeader, OrigPreheader);
+ DT.changeImmediateDominator(OrigHeader, OrigLatch);
// Brute force incremental dominator tree update. Call
// findNearestCommonDominator on all CFG predecessors of each child of the
// original header.
- DomTreeNode *OrigHeaderNode = DT->getNode(OrigHeader);
+ DomTreeNode *OrigHeaderNode = DT.getNode(OrigHeader);
SmallVector<DomTreeNode *, 8> HeaderChildren(OrigHeaderNode->begin(),
OrigHeaderNode->end());
bool Changed;
pred_iterator PI = pred_begin(BB);
BasicBlock *NearestDom = *PI;
for (pred_iterator PE = pred_end(BB); PI != PE; ++PI)
- NearestDom = DT->findNearestCommonDominator(NearestDom, *PI);
+ NearestDom = DT.findNearestCommonDominator(NearestDom, *PI);
// Remember if this changes the DomTree.
if (Node->getIDom()->getBlock() != NearestDom) {
- DT->changeImmediateDominator(BB, NearestDom);
+ DT.changeImmediateDominator(BB, NearestDom);
Changed = true;
}
}
++NumRotated;
return true;
}
-
projects / oota-llvm.git / blobdiff