#include "llvm/IntrinsicInst.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/CodeMetrics.h"
+#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/UnrollLoop.h"
+#include "llvm/Target/TargetData.h"
#include <climits>
using namespace llvm;
static cl::opt<unsigned>
-UnrollThreshold("unroll-threshold", cl::init(100), cl::Hidden,
+UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden,
cl::desc("The cut-off point for automatic loop unrolling"));
static cl::opt<unsigned>
cl::desc("Allows loops to be partially unrolled until "
"-unroll-threshold loop size is reached."));
+static cl::opt<bool>
+UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden,
+ cl::desc("Unroll loops with run-time trip counts"));
+
namespace {
class LoopUnroll : public LoopPass {
public:
static char ID; // Pass ID, replacement for typeid
- LoopUnroll() : LoopPass(&ID) {}
+ LoopUnroll(int T = -1, int C = -1, int P = -1) : LoopPass(ID) {
+ CurrentThreshold = (T == -1) ? UnrollThreshold : unsigned(T);
+ CurrentCount = (C == -1) ? UnrollCount : unsigned(C);
+ CurrentAllowPartial = (P == -1) ? UnrollAllowPartial : (bool)P;
+
+ UserThreshold = (T != -1) || (UnrollThreshold.getNumOccurrences() > 0);
+
+ initializeLoopUnrollPass(*PassRegistry::getPassRegistry());
+ }
/// A magic value for use with the Threshold parameter to indicate
/// that the loop unroll should be performed regardless of how much
/// code expansion would result.
static const unsigned NoThreshold = UINT_MAX;
+ // Threshold to use when optsize is specified (and there is no
+ // explicit -unroll-threshold).
+ static const unsigned OptSizeUnrollThreshold = 50;
+
+ // Default unroll count for loops with run-time trip count if
+ // -unroll-count is not set
+ static const unsigned UnrollRuntimeCount = 8;
+
+ unsigned CurrentCount;
+ unsigned CurrentThreshold;
+ bool CurrentAllowPartial;
+ bool UserThreshold; // CurrentThreshold is user-specified.
+
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.addRequired<LoopInfo>();
+ AU.addPreserved<LoopInfo>();
AU.addRequiredID(LoopSimplifyID);
+ AU.addPreservedID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
- AU.addRequired<LoopInfo>();
AU.addPreservedID(LCSSAID);
- AU.addPreserved<LoopInfo>();
+ AU.addRequired<ScalarEvolution>();
+ AU.addPreserved<ScalarEvolution>();
// FIXME: Loop unroll requires LCSSA. And LCSSA requires dom info.
// If loop unroll does not preserve dom info then LCSSA pass on next
// loop will receive invalid dom info.
// For now, recreate dom info, if loop is unrolled.
AU.addPreserved<DominatorTree>();
- AU.addPreserved<DominanceFrontier>();
}
};
}
char LoopUnroll::ID = 0;
-static RegisterPass<LoopUnroll> X("loop-unroll", "Unroll loops");
-
-Pass *llvm::createLoopUnrollPass() { return new LoopUnroll(); }
+INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
+INITIALIZE_PASS_DEPENDENCY(LoopInfo)
+INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
+INITIALIZE_PASS_DEPENDENCY(LCSSA)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
+INITIALIZE_PASS_END(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
+
+Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial) {
+ return new LoopUnroll(Threshold, Count, AllowPartial);
+}
/// ApproximateLoopSize - Approximate the size of the loop.
-static unsigned ApproximateLoopSize(const Loop *L) {
- unsigned Size = 0;
+static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls,
+ const TargetData *TD) {
+ CodeMetrics Metrics;
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
- I != E; ++I) {
- BasicBlock *BB = *I;
- Instruction *Term = BB->getTerminator();
- for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
- if (isa<PHINode>(I) && BB == L->getHeader()) {
- // Ignore PHI nodes in the header.
- } else if (I->hasOneUse() && I->use_back() == Term) {
- // Ignore instructions only used by the loop terminator.
- } else if (isa<DbgInfoIntrinsic>(I)) {
- // Ignore debug instructions
- } else if (isa<GetElementPtrInst>(I) && I->hasOneUse()) {
- // Ignore GEP as they generally are subsumed into a load or store.
- } else if (isa<CallInst>(I)) {
- // Estimate size overhead introduced by call instructions which
- // is higher than other instructions. Here 3 and 10 are magic
- // numbers that help one isolated test case from PR2067 without
- // negatively impacting measured benchmarks.
- Size += isa<IntrinsicInst>(I) ? 3 : 10;
- } else {
- ++Size;
- }
+ I != E; ++I)
+ Metrics.analyzeBasicBlock(*I, TD);
+ NumCalls = Metrics.NumInlineCandidates;
- // TODO: Ignore expressions derived from PHI and constants if inval of phi
- // is a constant, or if operation is associative. This will get induction
- // variables.
- }
- }
+ unsigned LoopSize = Metrics.NumInsts;
+
+ // Don't allow an estimate of size zero. This would allows unrolling of loops
+ // with huge iteration counts, which is a compile time problem even if it's
+ // not a problem for code quality.
+ if (LoopSize == 0) LoopSize = 1;
- return Size;
+ return LoopSize;
}
bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
- assert(L->isLCSSAForm());
LoopInfo *LI = &getAnalysis<LoopInfo>();
+ ScalarEvolution *SE = &getAnalysis<ScalarEvolution>();
BasicBlock *Header = L->getHeader();
- DEBUG(errs() << "Loop Unroll: F[" << Header->getParent()->getName()
+ DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName()
<< "] Loop %" << Header->getName() << "\n");
(void)Header;
- // Find trip count
- unsigned TripCount = L->getSmallConstantTripCount();
- unsigned Count = UnrollCount;
+ // Determine the current unrolling threshold. While this is normally set
+ // from UnrollThreshold, it is overridden to a smaller value if the current
+ // function is marked as optimize-for-size, and the unroll threshold was
+ // not user specified.
+ unsigned Threshold = CurrentThreshold;
+ if (!UserThreshold &&
+ Header->getParent()->hasFnAttr(Attribute::OptimizeForSize))
+ Threshold = OptSizeUnrollThreshold;
+
+ // Find trip count and trip multiple if count is not available
+ unsigned TripCount = 0;
+ unsigned TripMultiple = 1;
+ // Find "latch trip count". UnrollLoop assumes that control cannot exit
+ // via the loop latch on any iteration prior to TripCount. The loop may exit
+ // early via an earlier branch.
+ BasicBlock *LatchBlock = L->getLoopLatch();
+ if (LatchBlock) {
+ TripCount = SE->getSmallConstantTripCount(L, LatchBlock);
+ TripMultiple = SE->getSmallConstantTripMultiple(L, LatchBlock);
+ }
+ // Use a default unroll-count if the user doesn't specify a value
+ // and the trip count is a run-time value. The default is different
+ // for run-time or compile-time trip count loops.
+ unsigned Count = CurrentCount;
+ if (UnrollRuntime && CurrentCount == 0 && TripCount == 0)
+ Count = UnrollRuntimeCount;
- // Automatically select an unroll count.
if (Count == 0) {
// Conservative heuristic: if we know the trip count, see if we can
// completely unroll (subject to the threshold, checked below); otherwise
}
// Enforce the threshold.
- if (UnrollThreshold != NoThreshold) {
- unsigned LoopSize = ApproximateLoopSize(L);
- DEBUG(errs() << " Loop Size = " << LoopSize << "\n");
+ if (Threshold != NoThreshold) {
+ const TargetData *TD = getAnalysisIfAvailable<TargetData>();
+ unsigned NumInlineCandidates;
+ unsigned LoopSize = ApproximateLoopSize(L, NumInlineCandidates, TD);
+ DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n");
+ if (NumInlineCandidates != 0) {
+ DEBUG(dbgs() << " Not unrolling loop with inlinable calls.\n");
+ return false;
+ }
uint64_t Size = (uint64_t)LoopSize*Count;
- if (TripCount != 1 && Size > UnrollThreshold) {
- DEBUG(errs() << " Too large to fully unroll with count: " << Count
- << " because size: " << Size << ">" << UnrollThreshold << "\n");
- if (!UnrollAllowPartial) {
- DEBUG(errs() << " will not try to unroll partially because "
+ if (TripCount != 1 && Size > Threshold) {
+ DEBUG(dbgs() << " Too large to fully unroll with count: " << Count
+ << " because size: " << Size << ">" << Threshold << "\n");
+ if (!CurrentAllowPartial && !(UnrollRuntime && TripCount == 0)) {
+ DEBUG(dbgs() << " will not try to unroll partially because "
<< "-unroll-allow-partial not given\n");
return false;
}
- // Reduce unroll count to be modulo of TripCount for partial unrolling
- Count = UnrollThreshold / LoopSize;
- while (Count != 0 && TripCount%Count != 0) {
- Count--;
+ if (TripCount) {
+ // Reduce unroll count to be modulo of TripCount for partial unrolling
+ Count = CurrentThreshold / LoopSize;
+ while (Count != 0 && TripCount%Count != 0)
+ Count--;
+ }
+ else if (UnrollRuntime) {
+ // Reduce unroll count to be a lower power-of-two value
+ while (Count != 0 && Size > CurrentThreshold) {
+ Count >>= 1;
+ Size = LoopSize*Count;
+ }
}
if (Count < 2) {
- DEBUG(errs() << " could not unroll partially\n");
+ DEBUG(dbgs() << " could not unroll partially\n");
return false;
}
- DEBUG(errs() << " partially unrolling with count: " << Count << "\n");
+ DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n");
}
}
// Unroll the loop.
- Function *F = L->getHeader()->getParent();
- if (!UnrollLoop(L, Count, LI, &LPM))
+ if (!UnrollLoop(L, Count, TripCount, UnrollRuntime, TripMultiple, LI, &LPM))
return false;
- // FIXME: Reconstruct dom info, because it is not preserved properly.
- DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
- if (DT) {
- DT->runOnFunction(*F);
- DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
- if (DF)
- DF->runOnFunction(*F);
- }
return true;
}