#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;
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:
CurrentAllowPartial = (P == -1) ? UnrollAllowPartial : (bool)P;
UserThreshold = (T != -1) || (UnrollThreshold.getNumOccurrences() > 0);
-
+
initializeLoopUnrollPass(*PassRegistry::getPassRegistry());
}
/// 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;
AU.addPreservedID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addPreservedID(LCSSAID);
+ 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
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) {
}
/// ApproximateLoopSize - Approximate the size of the loop.
-static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls) {
+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)
- Metrics.analyzeBasicBlock(*I);
+ Metrics.analyzeBasicBlock(*I, TD);
NumCalls = Metrics.NumInlineCandidates;
-
+
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 LoopSize;
}
bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
LoopInfo *LI = &getAnalysis<LoopInfo>();
+ ScalarEvolution *SE = &getAnalysis<ScalarEvolution>();
BasicBlock *Header = L->getHeader();
DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName()
<< "] Loop %" << Header->getName() << "\n");
(void)Header;
-
+
// 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 &&
+ if (!UserThreshold &&
Header->getParent()->hasFnAttr(Attribute::OptimizeForSize))
Threshold = OptSizeUnrollThreshold;
- // Find trip count
- unsigned TripCount = L->getSmallConstantTripCount();
+ // 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 (Threshold != NoThreshold) {
+ const TargetData *TD = getAnalysisIfAvailable<TargetData>();
unsigned NumInlineCandidates;
- unsigned LoopSize = ApproximateLoopSize(L, 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");
if (TripCount != 1 && Size > Threshold) {
DEBUG(dbgs() << " Too large to fully unroll with count: " << Count
<< " because size: " << Size << ">" << Threshold << "\n");
- if (!CurrentAllowPartial) {
+ 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 = Threshold / 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(dbgs() << " could not unroll partially\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.
- if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>())
- DT->runOnFunction(*F);
return true;
}
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