diff options
Diffstat (limited to 'contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp | 404 |
1 files changed, 326 insertions, 78 deletions
diff --git a/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp index 08ac38d..935f289 100644 --- a/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp +++ b/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp @@ -12,14 +12,16 @@ // counts of loops easily. //===----------------------------------------------------------------------===// -#define DEBUG_TYPE "loop-unroll" #include "llvm/Transforms/Scalar.h" #include "llvm/Analysis/CodeMetrics.h" #include "llvm/Analysis/LoopPass.h" #include "llvm/Analysis/ScalarEvolution.h" #include "llvm/Analysis/TargetTransformInfo.h" #include "llvm/IR/DataLayout.h" +#include "llvm/IR/DiagnosticInfo.h" +#include "llvm/IR/Dominators.h" #include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Metadata.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" @@ -28,13 +30,16 @@ using namespace llvm; +#define DEBUG_TYPE "loop-unroll" + static cl::opt<unsigned> UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden, cl::desc("The cut-off point for automatic loop unrolling")); static cl::opt<unsigned> UnrollCount("unroll-count", cl::init(0), cl::Hidden, - cl::desc("Use this unroll count for all loops, for testing purposes")); + cl::desc("Use this unroll count for all loops including those with " + "unroll_count pragma values, for testing purposes")); static cl::opt<bool> UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden, @@ -45,6 +50,11 @@ static cl::opt<bool> UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden, cl::desc("Unroll loops with run-time trip counts")); +static cl::opt<unsigned> +PragmaUnrollThreshold("pragma-unroll-threshold", cl::init(16 * 1024), cl::Hidden, + cl::desc("Unrolled size limit for loops with an unroll(enable) or " + "unroll_count pragma.")); + namespace { class LoopUnroll : public LoopPass { public: @@ -86,12 +96,12 @@ namespace { bool UserAllowPartial; // CurrentAllowPartial is user-specified. bool UserRuntime; // CurrentRuntime is user-specified. - bool runOnLoop(Loop *L, LPPassManager &LPM); + bool runOnLoop(Loop *L, LPPassManager &LPM) override; /// This transformation requires natural loop information & requires that /// loop preheaders be inserted into the CFG... /// - virtual void getAnalysisUsage(AnalysisUsage &AU) const { + void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequired<LoopInfo>(); AU.addPreserved<LoopInfo>(); AU.addRequiredID(LoopSimplifyID); @@ -105,7 +115,67 @@ namespace { // 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<DominatorTreeWrapperPass>(); + } + + // Fill in the UnrollingPreferences parameter with values from the + // TargetTransformationInfo. + void getUnrollingPreferences(Loop *L, const TargetTransformInfo &TTI, + TargetTransformInfo::UnrollingPreferences &UP) { + UP.Threshold = CurrentThreshold; + UP.OptSizeThreshold = OptSizeUnrollThreshold; + UP.PartialThreshold = CurrentThreshold; + UP.PartialOptSizeThreshold = OptSizeUnrollThreshold; + UP.Count = CurrentCount; + UP.MaxCount = UINT_MAX; + UP.Partial = CurrentAllowPartial; + UP.Runtime = CurrentRuntime; + TTI.getUnrollingPreferences(L, UP); + } + + // Select and return an unroll count based on parameters from + // user, unroll preferences, unroll pragmas, or a heuristic. + // SetExplicitly is set to true if the unroll count is is set by + // the user or a pragma rather than selected heuristically. + unsigned + selectUnrollCount(const Loop *L, unsigned TripCount, bool HasEnablePragma, + unsigned PragmaCount, + const TargetTransformInfo::UnrollingPreferences &UP, + bool &SetExplicitly); + + + // Select threshold values used to limit unrolling based on a + // total unrolled size. Parameters Threshold and PartialThreshold + // are set to the maximum unrolled size for fully and partially + // unrolled loops respectively. + void selectThresholds(const Loop *L, bool HasPragma, + const TargetTransformInfo::UnrollingPreferences &UP, + unsigned &Threshold, unsigned &PartialThreshold) { + // 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. + Threshold = UserThreshold ? CurrentThreshold : UP.Threshold; + PartialThreshold = UserThreshold ? CurrentThreshold : UP.PartialThreshold; + if (!UserThreshold && + L->getHeader()->getParent()->getAttributes(). + hasAttribute(AttributeSet::FunctionIndex, + Attribute::OptimizeForSize)) { + Threshold = UP.OptSizeThreshold; + PartialThreshold = UP.PartialOptSizeThreshold; + } + if (HasPragma) { + // If the loop has an unrolling pragma, we want to be more + // aggressive with unrolling limits. Set thresholds to at + // least the PragmaTheshold value which is larger than the + // default limits. + if (Threshold != NoThreshold) + Threshold = std::max<unsigned>(Threshold, PragmaUnrollThreshold); + if (PartialThreshold != NoThreshold) + PartialThreshold = + std::max<unsigned>(PartialThreshold, PragmaUnrollThreshold); + } } }; } @@ -124,6 +194,10 @@ Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial, return new LoopUnroll(Threshold, Count, AllowPartial, Runtime); } +Pass *llvm::createSimpleLoopUnrollPass() { + return llvm::createLoopUnrollPass(-1, -1, 0, 0); +} + /// ApproximateLoopSize - Approximate the size of the loop. static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, bool &NotDuplicatable, @@ -145,7 +219,144 @@ static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, return LoopSize; } +// Returns the value associated with the given metadata node name (for +// example, "llvm.loop.unroll.count"). If no such named metadata node +// exists, then nullptr is returned. +static const ConstantInt *GetUnrollMetadataValue(const Loop *L, + StringRef Name) { + MDNode *LoopID = L->getLoopID(); + if (!LoopID) return nullptr; + + // First operand should refer to the loop id itself. + assert(LoopID->getNumOperands() > 0 && "requires at least one operand"); + assert(LoopID->getOperand(0) == LoopID && "invalid loop id"); + + for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) { + const MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i)); + if (!MD) continue; + + const MDString *S = dyn_cast<MDString>(MD->getOperand(0)); + if (!S) continue; + + if (Name.equals(S->getString())) { + assert(MD->getNumOperands() == 2 && + "Unroll hint metadata should have two operands."); + return cast<ConstantInt>(MD->getOperand(1)); + } + } + return nullptr; +} + +// Returns true if the loop has an unroll(enable) pragma. +static bool HasUnrollEnablePragma(const Loop *L) { + const ConstantInt *EnableValue = + GetUnrollMetadataValue(L, "llvm.loop.unroll.enable"); + return (EnableValue && EnableValue->getZExtValue()); +} + +// Returns true if the loop has an unroll(disable) pragma. +static bool HasUnrollDisablePragma(const Loop *L) { + const ConstantInt *EnableValue = + GetUnrollMetadataValue(L, "llvm.loop.unroll.enable"); + return (EnableValue && !EnableValue->getZExtValue()); +} + +// If loop has an unroll_count pragma return the (necessarily +// positive) value from the pragma. Otherwise return 0. +static unsigned UnrollCountPragmaValue(const Loop *L) { + const ConstantInt *CountValue = + GetUnrollMetadataValue(L, "llvm.loop.unroll.count"); + if (CountValue) { + unsigned Count = CountValue->getZExtValue(); + assert(Count >= 1 && "Unroll count must be positive."); + return Count; + } + return 0; +} + +// Remove existing unroll metadata and add unroll disable metadata to +// indicate the loop has already been unrolled. This prevents a loop +// from being unrolled more than is directed by a pragma if the loop +// unrolling pass is run more than once (which it generally is). +static void SetLoopAlreadyUnrolled(Loop *L) { + MDNode *LoopID = L->getLoopID(); + if (!LoopID) return; + + // First remove any existing loop unrolling metadata. + SmallVector<Value *, 4> Vals; + // Reserve first location for self reference to the LoopID metadata node. + Vals.push_back(nullptr); + for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) { + bool IsUnrollMetadata = false; + MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i)); + if (MD) { + const MDString *S = dyn_cast<MDString>(MD->getOperand(0)); + IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll."); + } + if (!IsUnrollMetadata) Vals.push_back(LoopID->getOperand(i)); + } + + // Add unroll(disable) metadata to disable future unrolling. + LLVMContext &Context = L->getHeader()->getContext(); + SmallVector<Value *, 2> DisableOperands; + DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.enable")); + DisableOperands.push_back(ConstantInt::get(Type::getInt1Ty(Context), 0)); + MDNode *DisableNode = MDNode::get(Context, DisableOperands); + Vals.push_back(DisableNode); + + MDNode *NewLoopID = MDNode::get(Context, Vals); + // Set operand 0 to refer to the loop id itself. + NewLoopID->replaceOperandWith(0, NewLoopID); + L->setLoopID(NewLoopID); + LoopID->replaceAllUsesWith(NewLoopID); +} + +unsigned LoopUnroll::selectUnrollCount( + const Loop *L, unsigned TripCount, bool HasEnablePragma, + unsigned PragmaCount, const TargetTransformInfo::UnrollingPreferences &UP, + bool &SetExplicitly) { + SetExplicitly = true; + + // User-specified count (either as a command-line option or + // constructor parameter) has highest precedence. + unsigned Count = UserCount ? CurrentCount : 0; + + // If there is no user-specified count, unroll pragmas have the next + // highest precendence. + if (Count == 0) { + if (PragmaCount) { + Count = PragmaCount; + } else if (HasEnablePragma) { + // unroll(enable) pragma without an unroll_count pragma + // indicates to unroll loop fully. + Count = TripCount; + } + } + + if (Count == 0) + Count = UP.Count; + + if (Count == 0) { + SetExplicitly = false; + if (TripCount == 0) + // Runtime trip count. + Count = UnrollRuntimeCount; + else + // Conservative heuristic: if we know the trip count, see if we can + // completely unroll (subject to the threshold, checked below); otherwise + // try to find greatest modulo of the trip count which is still under + // threshold value. + Count = TripCount; + } + if (TripCount && Count > TripCount) + return TripCount; + return Count; +} + bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { + if (skipOptnoneFunction(L)) + return false; + LoopInfo *LI = &getAnalysis<LoopInfo>(); ScalarEvolution *SE = &getAnalysis<ScalarEvolution>(); const TargetTransformInfo &TTI = getAnalysis<TargetTransformInfo>(); @@ -153,26 +364,16 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { BasicBlock *Header = L->getHeader(); DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName() << "] Loop %" << Header->getName() << "\n"); - (void)Header; + + if (HasUnrollDisablePragma(L)) { + return false; + } + bool HasEnablePragma = HasUnrollEnablePragma(L); + unsigned PragmaCount = UnrollCountPragmaValue(L); + bool HasPragma = HasEnablePragma || PragmaCount > 0; TargetTransformInfo::UnrollingPreferences UP; - UP.Threshold = CurrentThreshold; - UP.OptSizeThreshold = OptSizeUnrollThreshold; - UP.Count = CurrentCount; - UP.Partial = CurrentAllowPartial; - UP.Runtime = CurrentRuntime; - TTI.getUnrollingPreferences(L, UP); - - // 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 = UserThreshold ? CurrentThreshold : UP.Threshold; - if (!UserThreshold && - Header->getParent()->getAttributes(). - hasAttribute(AttributeSet::FunctionIndex, - Attribute::OptimizeForSize)) - Threshold = UP.OptSizeThreshold; + getUnrollingPreferences(L, TTI, UP); // Find trip count and trip multiple if count is not available unsigned TripCount = 0; @@ -186,74 +387,121 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { TripMultiple = SE->getSmallConstantTripMultiple(L, LatchBlock); } - bool Runtime = UserRuntime ? CurrentRuntime : UP.Runtime; + // Select an initial unroll count. This may be reduced later based + // on size thresholds. + bool CountSetExplicitly; + unsigned Count = selectUnrollCount(L, TripCount, HasEnablePragma, PragmaCount, + UP, CountSetExplicitly); + + unsigned NumInlineCandidates; + bool notDuplicatable; + unsigned LoopSize = + ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI); + DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n"); + uint64_t UnrolledSize = (uint64_t)LoopSize * Count; + if (notDuplicatable) { + DEBUG(dbgs() << " Not unrolling loop which contains non-duplicatable" + << " instructions.\n"); + return false; + } + if (NumInlineCandidates != 0) { + DEBUG(dbgs() << " Not unrolling loop with inlinable calls.\n"); + return false; + } - // 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 = UserCount ? CurrentCount : UP.Count; - if (Runtime && Count == 0 && TripCount == 0) - Count = UnrollRuntimeCount; + unsigned Threshold, PartialThreshold; + selectThresholds(L, HasPragma, UP, Threshold, PartialThreshold); - if (Count == 0) { - // Conservative heuristic: if we know the trip count, see if we can - // completely unroll (subject to the threshold, checked below); otherwise - // try to find greatest modulo of the trip count which is still under - // threshold value. - if (TripCount == 0) - return false; - Count = TripCount; + // Given Count, TripCount and thresholds determine the type of + // unrolling which is to be performed. + enum { Full = 0, Partial = 1, Runtime = 2 }; + int Unrolling; + if (TripCount && Count == TripCount) { + if (Threshold != NoThreshold && UnrolledSize > Threshold) { + DEBUG(dbgs() << " Too large to fully unroll with count: " << Count + << " because size: " << UnrolledSize << ">" << Threshold + << "\n"); + Unrolling = Partial; + } else { + Unrolling = Full; + } + } else if (TripCount && Count < TripCount) { + Unrolling = Partial; + } else { + Unrolling = Runtime; } - // Enforce the threshold. - if (Threshold != NoThreshold) { - unsigned NumInlineCandidates; - bool notDuplicatable; - unsigned LoopSize = ApproximateLoopSize(L, NumInlineCandidates, - notDuplicatable, TTI); - DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n"); - if (notDuplicatable) { - DEBUG(dbgs() << " Not unrolling loop which contains non duplicatable" - << " instructions.\n"); + // Reduce count based on the type of unrolling and the threshold values. + unsigned OriginalCount = Count; + bool AllowRuntime = UserRuntime ? CurrentRuntime : UP.Runtime; + if (Unrolling == Partial) { + bool AllowPartial = UserAllowPartial ? CurrentAllowPartial : UP.Partial; + if (!AllowPartial && !CountSetExplicitly) { + DEBUG(dbgs() << " will not try to unroll partially because " + << "-unroll-allow-partial not given\n"); return false; } - if (NumInlineCandidates != 0) { - DEBUG(dbgs() << " Not unrolling loop with inlinable calls.\n"); + if (PartialThreshold != NoThreshold && UnrolledSize > PartialThreshold) { + // Reduce unroll count to be modulo of TripCount for partial unrolling. + Count = PartialThreshold / LoopSize; + while (Count != 0 && TripCount % Count != 0) + Count--; + } + } else if (Unrolling == Runtime) { + if (!AllowRuntime && !CountSetExplicitly) { + DEBUG(dbgs() << " will not try to unroll loop with runtime trip count " + << "-unroll-runtime not given\n"); return false; } - uint64_t Size = (uint64_t)LoopSize*Count; - if (TripCount != 1 && Size > Threshold) { - DEBUG(dbgs() << " Too large to fully unroll with count: " << Count - << " because size: " << Size << ">" << Threshold << "\n"); - bool AllowPartial = UserAllowPartial ? CurrentAllowPartial : UP.Partial; - if (!AllowPartial && !(Runtime && TripCount == 0)) { - DEBUG(dbgs() << " will not try to unroll partially because " - << "-unroll-allow-partial not given\n"); - return false; - } - if (TripCount) { - // Reduce unroll count to be modulo of TripCount for partial unrolling - Count = Threshold / LoopSize; - while (Count != 0 && TripCount%Count != 0) - Count--; - } - else if (Runtime) { - // Reduce unroll count to be a lower power-of-two value - while (Count != 0 && Size > Threshold) { - Count >>= 1; - Size = LoopSize*Count; - } - } - if (Count < 2) { - DEBUG(dbgs() << " could not unroll partially\n"); - return false; + // Reduce unroll count to be the largest power-of-two factor of + // the original count which satisfies the threshold limit. + while (Count != 0 && UnrolledSize > PartialThreshold) { + Count >>= 1; + UnrolledSize = LoopSize * Count; + } + if (Count > UP.MaxCount) + Count = UP.MaxCount; + DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n"); + } + + if (HasPragma) { + // Mark loop as unrolled to prevent unrolling beyond that + // requested by the pragma. + SetLoopAlreadyUnrolled(L); + + // Emit optimization remarks if we are unable to unroll the loop + // as directed by a pragma. + DebugLoc LoopLoc = L->getStartLoc(); + Function *F = Header->getParent(); + LLVMContext &Ctx = F->getContext(); + if (HasEnablePragma && PragmaCount == 0) { + if (TripCount && Count != TripCount) { + emitOptimizationRemarkMissed( + Ctx, DEBUG_TYPE, *F, LoopLoc, + "Unable to fully unroll loop as directed by unroll(enable) pragma " + "because unrolled size is too large."); + } else if (!TripCount) { + emitOptimizationRemarkMissed( + Ctx, DEBUG_TYPE, *F, LoopLoc, + "Unable to fully unroll loop as directed by unroll(enable) pragma " + "because loop has a runtime trip count."); } - DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n"); + } else if (PragmaCount > 0 && Count != OriginalCount) { + emitOptimizationRemarkMissed( + Ctx, DEBUG_TYPE, *F, LoopLoc, + "Unable to unroll loop the number of times directed by " + "unroll_count pragma because unrolled size is too large."); } } + if (Unrolling != Full && Count < 2) { + // Partial unrolling by 1 is a nop. For full unrolling, a factor + // of 1 makes sense because loop control can be eliminated. + return false; + } + // Unroll the loop. - if (!UnrollLoop(L, Count, TripCount, Runtime, TripMultiple, LI, &LPM)) + if (!UnrollLoop(L, Count, TripCount, AllowRuntime, TripMultiple, LI, this, &LPM)) return false; return true; |
