1088 lines
43 KiB
C++
1088 lines
43 KiB
C++
//===-- LoopUnroll.cpp - Loop unroller pass -------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass implements a simple loop unroller. It works best when loops have
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// been canonicalized by the -indvars pass, allowing it to determine the trip
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// counts of loops easily.
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/Analysis/GlobalsModRef.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/CodeMetrics.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DiagnosticInfo.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/InstVisitor.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/UnrollLoop.h"
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#include <climits>
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using namespace llvm;
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#define DEBUG_TYPE "loop-unroll"
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static cl::opt<unsigned>
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UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden,
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cl::desc("The baseline cost threshold for loop unrolling"));
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static cl::opt<unsigned> UnrollPercentDynamicCostSavedThreshold(
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"unroll-percent-dynamic-cost-saved-threshold", cl::init(20), cl::Hidden,
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cl::desc("The percentage of estimated dynamic cost which must be saved by "
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"unrolling to allow unrolling up to the max threshold."));
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static cl::opt<unsigned> UnrollDynamicCostSavingsDiscount(
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"unroll-dynamic-cost-savings-discount", cl::init(2000), cl::Hidden,
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cl::desc("This is the amount discounted from the total unroll cost when "
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"the unrolled form has a high dynamic cost savings (triggered by "
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"the '-unroll-perecent-dynamic-cost-saved-threshold' flag)."));
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static cl::opt<unsigned> UnrollMaxIterationsCountToAnalyze(
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"unroll-max-iteration-count-to-analyze", cl::init(0), cl::Hidden,
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cl::desc("Don't allow loop unrolling to simulate more than this number of"
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"iterations when checking full unroll profitability"));
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static cl::opt<unsigned>
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UnrollCount("unroll-count", cl::init(0), cl::Hidden,
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cl::desc("Use this unroll count for all loops including those with "
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"unroll_count pragma values, for testing purposes"));
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static cl::opt<bool>
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UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden,
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cl::desc("Allows loops to be partially unrolled until "
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"-unroll-threshold loop size is reached."));
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static cl::opt<bool>
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UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden,
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cl::desc("Unroll loops with run-time trip counts"));
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static cl::opt<unsigned>
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PragmaUnrollThreshold("pragma-unroll-threshold", cl::init(16 * 1024), cl::Hidden,
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cl::desc("Unrolled size limit for loops with an unroll(full) or "
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"unroll_count pragma."));
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namespace {
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class LoopUnroll : public LoopPass {
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public:
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static char ID; // Pass ID, replacement for typeid
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LoopUnroll(int T = -1, int C = -1, int P = -1, int R = -1) : LoopPass(ID) {
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CurrentThreshold = (T == -1) ? UnrollThreshold : unsigned(T);
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CurrentPercentDynamicCostSavedThreshold =
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UnrollPercentDynamicCostSavedThreshold;
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CurrentDynamicCostSavingsDiscount = UnrollDynamicCostSavingsDiscount;
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CurrentCount = (C == -1) ? UnrollCount : unsigned(C);
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CurrentAllowPartial = (P == -1) ? UnrollAllowPartial : (bool)P;
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CurrentRuntime = (R == -1) ? UnrollRuntime : (bool)R;
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UserThreshold = (T != -1) || (UnrollThreshold.getNumOccurrences() > 0);
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UserPercentDynamicCostSavedThreshold =
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(UnrollPercentDynamicCostSavedThreshold.getNumOccurrences() > 0);
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UserDynamicCostSavingsDiscount =
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(UnrollDynamicCostSavingsDiscount.getNumOccurrences() > 0);
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UserAllowPartial = (P != -1) ||
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(UnrollAllowPartial.getNumOccurrences() > 0);
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UserRuntime = (R != -1) || (UnrollRuntime.getNumOccurrences() > 0);
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UserCount = (C != -1) || (UnrollCount.getNumOccurrences() > 0);
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initializeLoopUnrollPass(*PassRegistry::getPassRegistry());
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}
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/// A magic value for use with the Threshold parameter to indicate
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/// that the loop unroll should be performed regardless of how much
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/// code expansion would result.
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static const unsigned NoThreshold = UINT_MAX;
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// Threshold to use when optsize is specified (and there is no
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// explicit -unroll-threshold).
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static const unsigned OptSizeUnrollThreshold = 50;
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// Default unroll count for loops with run-time trip count if
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// -unroll-count is not set
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static const unsigned UnrollRuntimeCount = 8;
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unsigned CurrentCount;
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unsigned CurrentThreshold;
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unsigned CurrentPercentDynamicCostSavedThreshold;
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unsigned CurrentDynamicCostSavingsDiscount;
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bool CurrentAllowPartial;
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bool CurrentRuntime;
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// Flags for whether the 'current' settings are user-specified.
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bool UserCount;
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bool UserThreshold;
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bool UserPercentDynamicCostSavedThreshold;
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bool UserDynamicCostSavingsDiscount;
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bool UserAllowPartial;
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bool UserRuntime;
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bool runOnLoop(Loop *L, LPPassManager &LPM) override;
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/// This transformation requires natural loop information & requires that
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/// loop preheaders be inserted into the CFG...
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///
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<AssumptionCacheTracker>();
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addRequired<LoopInfoWrapperPass>();
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AU.addPreserved<LoopInfoWrapperPass>();
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AU.addRequiredID(LoopSimplifyID);
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AU.addPreservedID(LoopSimplifyID);
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AU.addRequiredID(LCSSAID);
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AU.addPreservedID(LCSSAID);
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AU.addRequired<ScalarEvolutionWrapperPass>();
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AU.addPreserved<ScalarEvolutionWrapperPass>();
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AU.addRequired<TargetTransformInfoWrapperPass>();
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// FIXME: Loop unroll requires LCSSA. And LCSSA requires dom info.
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// If loop unroll does not preserve dom info then LCSSA pass on next
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// loop will receive invalid dom info.
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// For now, recreate dom info, if loop is unrolled.
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AU.addPreserved<DominatorTreeWrapperPass>();
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AU.addPreserved<GlobalsAAWrapperPass>();
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}
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// Fill in the UnrollingPreferences parameter with values from the
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// TargetTransformationInfo.
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void getUnrollingPreferences(Loop *L, const TargetTransformInfo &TTI,
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TargetTransformInfo::UnrollingPreferences &UP) {
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UP.Threshold = CurrentThreshold;
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UP.PercentDynamicCostSavedThreshold =
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CurrentPercentDynamicCostSavedThreshold;
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UP.DynamicCostSavingsDiscount = CurrentDynamicCostSavingsDiscount;
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UP.OptSizeThreshold = OptSizeUnrollThreshold;
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UP.PartialThreshold = CurrentThreshold;
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UP.PartialOptSizeThreshold = OptSizeUnrollThreshold;
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UP.Count = CurrentCount;
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UP.MaxCount = UINT_MAX;
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UP.Partial = CurrentAllowPartial;
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UP.Runtime = CurrentRuntime;
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UP.AllowExpensiveTripCount = false;
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TTI.getUnrollingPreferences(L, UP);
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}
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// Select and return an unroll count based on parameters from
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// user, unroll preferences, unroll pragmas, or a heuristic.
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// SetExplicitly is set to true if the unroll count is is set by
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// the user or a pragma rather than selected heuristically.
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unsigned
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selectUnrollCount(const Loop *L, unsigned TripCount, bool PragmaFullUnroll,
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unsigned PragmaCount,
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const TargetTransformInfo::UnrollingPreferences &UP,
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bool &SetExplicitly);
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// Select threshold values used to limit unrolling based on a
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// total unrolled size. Parameters Threshold and PartialThreshold
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// are set to the maximum unrolled size for fully and partially
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// unrolled loops respectively.
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void selectThresholds(const Loop *L, bool UsePragmaThreshold,
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const TargetTransformInfo::UnrollingPreferences &UP,
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unsigned &Threshold, unsigned &PartialThreshold,
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unsigned &PercentDynamicCostSavedThreshold,
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unsigned &DynamicCostSavingsDiscount) {
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// Determine the current unrolling threshold. While this is
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// normally set from UnrollThreshold, it is overridden to a
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// smaller value if the current function is marked as
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// optimize-for-size, and the unroll threshold was not user
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// specified.
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Threshold = UserThreshold ? CurrentThreshold : UP.Threshold;
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PartialThreshold = UserThreshold ? CurrentThreshold : UP.PartialThreshold;
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PercentDynamicCostSavedThreshold =
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UserPercentDynamicCostSavedThreshold
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? CurrentPercentDynamicCostSavedThreshold
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: UP.PercentDynamicCostSavedThreshold;
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DynamicCostSavingsDiscount = UserDynamicCostSavingsDiscount
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? CurrentDynamicCostSavingsDiscount
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: UP.DynamicCostSavingsDiscount;
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if (!UserThreshold &&
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// FIXME: Use Function::optForSize().
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L->getHeader()->getParent()->hasFnAttribute(
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Attribute::OptimizeForSize)) {
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Threshold = UP.OptSizeThreshold;
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PartialThreshold = UP.PartialOptSizeThreshold;
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}
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if (UsePragmaThreshold) {
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// If the loop has an unrolling pragma, we want to be more
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// aggressive with unrolling limits. Set thresholds to at
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// least the PragmaTheshold value which is larger than the
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// default limits.
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if (Threshold != NoThreshold)
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Threshold = std::max<unsigned>(Threshold, PragmaUnrollThreshold);
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if (PartialThreshold != NoThreshold)
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PartialThreshold =
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std::max<unsigned>(PartialThreshold, PragmaUnrollThreshold);
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}
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}
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bool canUnrollCompletely(Loop *L, unsigned Threshold,
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unsigned PercentDynamicCostSavedThreshold,
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unsigned DynamicCostSavingsDiscount,
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uint64_t UnrolledCost, uint64_t RolledDynamicCost);
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};
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}
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char LoopUnroll::ID = 0;
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INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
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INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
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INITIALIZE_PASS_DEPENDENCY(LCSSA)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
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INITIALIZE_PASS_END(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
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Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial,
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int Runtime) {
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return new LoopUnroll(Threshold, Count, AllowPartial, Runtime);
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}
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Pass *llvm::createSimpleLoopUnrollPass() {
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return llvm::createLoopUnrollPass(-1, -1, 0, 0);
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}
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namespace {
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// This class is used to get an estimate of the optimization effects that we
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// could get from complete loop unrolling. It comes from the fact that some
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// loads might be replaced with concrete constant values and that could trigger
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// a chain of instruction simplifications.
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//
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// E.g. we might have:
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// int a[] = {0, 1, 0};
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// v = 0;
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// for (i = 0; i < 3; i ++)
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// v += b[i]*a[i];
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// If we completely unroll the loop, we would get:
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// v = b[0]*a[0] + b[1]*a[1] + b[2]*a[2]
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// Which then will be simplified to:
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// v = b[0]* 0 + b[1]* 1 + b[2]* 0
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// And finally:
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// v = b[1]
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class UnrolledInstAnalyzer : private InstVisitor<UnrolledInstAnalyzer, bool> {
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typedef InstVisitor<UnrolledInstAnalyzer, bool> Base;
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friend class InstVisitor<UnrolledInstAnalyzer, bool>;
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struct SimplifiedAddress {
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Value *Base = nullptr;
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ConstantInt *Offset = nullptr;
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};
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public:
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UnrolledInstAnalyzer(unsigned Iteration,
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DenseMap<Value *, Constant *> &SimplifiedValues,
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ScalarEvolution &SE)
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: SimplifiedValues(SimplifiedValues), SE(SE) {
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IterationNumber = SE.getConstant(APInt(64, Iteration));
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}
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// Allow access to the initial visit method.
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using Base::visit;
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private:
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/// \brief A cache of pointer bases and constant-folded offsets corresponding
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/// to GEP (or derived from GEP) instructions.
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///
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/// In order to find the base pointer one needs to perform non-trivial
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/// traversal of the corresponding SCEV expression, so it's good to have the
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/// results saved.
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DenseMap<Value *, SimplifiedAddress> SimplifiedAddresses;
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/// \brief SCEV expression corresponding to number of currently simulated
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/// iteration.
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const SCEV *IterationNumber;
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/// \brief A Value->Constant map for keeping values that we managed to
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/// constant-fold on the given iteration.
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///
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/// While we walk the loop instructions, we build up and maintain a mapping
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/// of simplified values specific to this iteration. The idea is to propagate
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/// any special information we have about loads that can be replaced with
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/// constants after complete unrolling, and account for likely simplifications
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/// post-unrolling.
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DenseMap<Value *, Constant *> &SimplifiedValues;
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ScalarEvolution &SE;
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/// \brief Try to simplify instruction \param I using its SCEV expression.
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///
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/// The idea is that some AddRec expressions become constants, which then
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/// could trigger folding of other instructions. However, that only happens
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/// for expressions whose start value is also constant, which isn't always the
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/// case. In another common and important case the start value is just some
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/// address (i.e. SCEVUnknown) - in this case we compute the offset and save
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/// it along with the base address instead.
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bool simplifyInstWithSCEV(Instruction *I) {
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if (!SE.isSCEVable(I->getType()))
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return false;
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const SCEV *S = SE.getSCEV(I);
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if (auto *SC = dyn_cast<SCEVConstant>(S)) {
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SimplifiedValues[I] = SC->getValue();
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return true;
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}
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auto *AR = dyn_cast<SCEVAddRecExpr>(S);
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if (!AR)
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return false;
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const SCEV *ValueAtIteration = AR->evaluateAtIteration(IterationNumber, SE);
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// Check if the AddRec expression becomes a constant.
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if (auto *SC = dyn_cast<SCEVConstant>(ValueAtIteration)) {
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SimplifiedValues[I] = SC->getValue();
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return true;
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}
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// Check if the offset from the base address becomes a constant.
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auto *Base = dyn_cast<SCEVUnknown>(SE.getPointerBase(S));
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if (!Base)
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return false;
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auto *Offset =
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dyn_cast<SCEVConstant>(SE.getMinusSCEV(ValueAtIteration, Base));
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if (!Offset)
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return false;
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SimplifiedAddress Address;
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Address.Base = Base->getValue();
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Address.Offset = Offset->getValue();
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SimplifiedAddresses[I] = Address;
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return true;
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}
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/// Base case for the instruction visitor.
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bool visitInstruction(Instruction &I) {
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return simplifyInstWithSCEV(&I);
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}
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/// Try to simplify binary operator I.
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///
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/// TODO: Probably it's worth to hoist the code for estimating the
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/// simplifications effects to a separate class, since we have a very similar
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/// code in InlineCost already.
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bool visitBinaryOperator(BinaryOperator &I) {
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Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
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if (!isa<Constant>(LHS))
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if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS))
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LHS = SimpleLHS;
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if (!isa<Constant>(RHS))
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if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS))
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RHS = SimpleRHS;
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Value *SimpleV = nullptr;
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const DataLayout &DL = I.getModule()->getDataLayout();
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if (auto FI = dyn_cast<FPMathOperator>(&I))
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SimpleV =
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SimplifyFPBinOp(I.getOpcode(), LHS, RHS, FI->getFastMathFlags(), DL);
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else
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SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS, DL);
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if (Constant *C = dyn_cast_or_null<Constant>(SimpleV))
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SimplifiedValues[&I] = C;
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if (SimpleV)
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return true;
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return Base::visitBinaryOperator(I);
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}
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/// Try to fold load I.
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bool visitLoad(LoadInst &I) {
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Value *AddrOp = I.getPointerOperand();
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auto AddressIt = SimplifiedAddresses.find(AddrOp);
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if (AddressIt == SimplifiedAddresses.end())
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return false;
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ConstantInt *SimplifiedAddrOp = AddressIt->second.Offset;
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auto *GV = dyn_cast<GlobalVariable>(AddressIt->second.Base);
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// We're only interested in loads that can be completely folded to a
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// constant.
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if (!GV || !GV->hasDefinitiveInitializer() || !GV->isConstant())
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return false;
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ConstantDataSequential *CDS =
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dyn_cast<ConstantDataSequential>(GV->getInitializer());
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if (!CDS)
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return false;
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// We might have a vector load from an array. FIXME: for now we just bail
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// out in this case, but we should be able to resolve and simplify such
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// loads.
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if(!CDS->isElementTypeCompatible(I.getType()))
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return false;
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int ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U;
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assert(SimplifiedAddrOp->getValue().getActiveBits() < 64 &&
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"Unexpectedly large index value.");
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int64_t Index = SimplifiedAddrOp->getSExtValue() / ElemSize;
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if (Index >= CDS->getNumElements()) {
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// FIXME: For now we conservatively ignore out of bound accesses, but
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// we're allowed to perform the optimization in this case.
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return false;
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}
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Constant *CV = CDS->getElementAsConstant(Index);
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assert(CV && "Constant expected.");
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SimplifiedValues[&I] = CV;
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return true;
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}
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bool visitCastInst(CastInst &I) {
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// Propagate constants through casts.
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Constant *COp = dyn_cast<Constant>(I.getOperand(0));
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if (!COp)
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COp = SimplifiedValues.lookup(I.getOperand(0));
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if (COp)
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if (Constant *C =
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ConstantExpr::getCast(I.getOpcode(), COp, I.getType())) {
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SimplifiedValues[&I] = C;
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return true;
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}
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return Base::visitCastInst(I);
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}
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bool visitCmpInst(CmpInst &I) {
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Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
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// First try to handle simplified comparisons.
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if (!isa<Constant>(LHS))
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if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS))
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LHS = SimpleLHS;
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if (!isa<Constant>(RHS))
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if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS))
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RHS = SimpleRHS;
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if (!isa<Constant>(LHS) && !isa<Constant>(RHS)) {
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|
auto SimplifiedLHS = SimplifiedAddresses.find(LHS);
|
|
if (SimplifiedLHS != SimplifiedAddresses.end()) {
|
|
auto SimplifiedRHS = SimplifiedAddresses.find(RHS);
|
|
if (SimplifiedRHS != SimplifiedAddresses.end()) {
|
|
SimplifiedAddress &LHSAddr = SimplifiedLHS->second;
|
|
SimplifiedAddress &RHSAddr = SimplifiedRHS->second;
|
|
if (LHSAddr.Base == RHSAddr.Base) {
|
|
LHS = LHSAddr.Offset;
|
|
RHS = RHSAddr.Offset;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
|
|
if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
|
|
if (Constant *C = ConstantExpr::getCompare(I.getPredicate(), CLHS, CRHS)) {
|
|
SimplifiedValues[&I] = C;
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
|
|
return Base::visitCmpInst(I);
|
|
}
|
|
};
|
|
} // namespace
|
|
|
|
|
|
namespace {
|
|
struct EstimatedUnrollCost {
|
|
/// \brief The estimated cost after unrolling.
|
|
int UnrolledCost;
|
|
|
|
/// \brief The estimated dynamic cost of executing the instructions in the
|
|
/// rolled form.
|
|
int RolledDynamicCost;
|
|
};
|
|
}
|
|
|
|
/// \brief Figure out if the loop is worth full unrolling.
|
|
///
|
|
/// Complete loop unrolling can make some loads constant, and we need to know
|
|
/// if that would expose any further optimization opportunities. This routine
|
|
/// estimates this optimization. It computes cost of unrolled loop
|
|
/// (UnrolledCost) and dynamic cost of the original loop (RolledDynamicCost). By
|
|
/// dynamic cost we mean that we won't count costs of blocks that are known not
|
|
/// to be executed (i.e. if we have a branch in the loop and we know that at the
|
|
/// given iteration its condition would be resolved to true, we won't add up the
|
|
/// cost of the 'false'-block).
|
|
/// \returns Optional value, holding the RolledDynamicCost and UnrolledCost. If
|
|
/// the analysis failed (no benefits expected from the unrolling, or the loop is
|
|
/// too big to analyze), the returned value is None.
|
|
static Optional<EstimatedUnrollCost>
|
|
analyzeLoopUnrollCost(const Loop *L, unsigned TripCount, DominatorTree &DT,
|
|
ScalarEvolution &SE, const TargetTransformInfo &TTI,
|
|
int MaxUnrolledLoopSize) {
|
|
// We want to be able to scale offsets by the trip count and add more offsets
|
|
// to them without checking for overflows, and we already don't want to
|
|
// analyze *massive* trip counts, so we force the max to be reasonably small.
|
|
assert(UnrollMaxIterationsCountToAnalyze < (INT_MAX / 2) &&
|
|
"The unroll iterations max is too large!");
|
|
|
|
// Don't simulate loops with a big or unknown tripcount
|
|
if (!UnrollMaxIterationsCountToAnalyze || !TripCount ||
|
|
TripCount > UnrollMaxIterationsCountToAnalyze)
|
|
return None;
|
|
|
|
SmallSetVector<BasicBlock *, 16> BBWorklist;
|
|
DenseMap<Value *, Constant *> SimplifiedValues;
|
|
SmallVector<std::pair<Value *, Constant *>, 4> SimplifiedInputValues;
|
|
|
|
// The estimated cost of the unrolled form of the loop. We try to estimate
|
|
// this by simplifying as much as we can while computing the estimate.
|
|
int UnrolledCost = 0;
|
|
// We also track the estimated dynamic (that is, actually executed) cost in
|
|
// the rolled form. This helps identify cases when the savings from unrolling
|
|
// aren't just exposing dead control flows, but actual reduced dynamic
|
|
// instructions due to the simplifications which we expect to occur after
|
|
// unrolling.
|
|
int RolledDynamicCost = 0;
|
|
|
|
// Ensure that we don't violate the loop structure invariants relied on by
|
|
// this analysis.
|
|
assert(L->isLoopSimplifyForm() && "Must put loop into normal form first.");
|
|
assert(L->isLCSSAForm(DT) &&
|
|
"Must have loops in LCSSA form to track live-out values.");
|
|
|
|
DEBUG(dbgs() << "Starting LoopUnroll profitability analysis...\n");
|
|
|
|
// Simulate execution of each iteration of the loop counting instructions,
|
|
// which would be simplified.
|
|
// Since the same load will take different values on different iterations,
|
|
// we literally have to go through all loop's iterations.
|
|
for (unsigned Iteration = 0; Iteration < TripCount; ++Iteration) {
|
|
DEBUG(dbgs() << " Analyzing iteration " << Iteration << "\n");
|
|
|
|
// Prepare for the iteration by collecting any simplified entry or backedge
|
|
// inputs.
|
|
for (Instruction &I : *L->getHeader()) {
|
|
auto *PHI = dyn_cast<PHINode>(&I);
|
|
if (!PHI)
|
|
break;
|
|
|
|
// The loop header PHI nodes must have exactly two input: one from the
|
|
// loop preheader and one from the loop latch.
|
|
assert(
|
|
PHI->getNumIncomingValues() == 2 &&
|
|
"Must have an incoming value only for the preheader and the latch.");
|
|
|
|
Value *V = PHI->getIncomingValueForBlock(
|
|
Iteration == 0 ? L->getLoopPreheader() : L->getLoopLatch());
|
|
Constant *C = dyn_cast<Constant>(V);
|
|
if (Iteration != 0 && !C)
|
|
C = SimplifiedValues.lookup(V);
|
|
if (C)
|
|
SimplifiedInputValues.push_back({PHI, C});
|
|
}
|
|
|
|
// Now clear and re-populate the map for the next iteration.
|
|
SimplifiedValues.clear();
|
|
while (!SimplifiedInputValues.empty())
|
|
SimplifiedValues.insert(SimplifiedInputValues.pop_back_val());
|
|
|
|
UnrolledInstAnalyzer Analyzer(Iteration, SimplifiedValues, SE);
|
|
|
|
BBWorklist.clear();
|
|
BBWorklist.insert(L->getHeader());
|
|
// Note that we *must not* cache the size, this loop grows the worklist.
|
|
for (unsigned Idx = 0; Idx != BBWorklist.size(); ++Idx) {
|
|
BasicBlock *BB = BBWorklist[Idx];
|
|
|
|
// Visit all instructions in the given basic block and try to simplify
|
|
// it. We don't change the actual IR, just count optimization
|
|
// opportunities.
|
|
for (Instruction &I : *BB) {
|
|
int InstCost = TTI.getUserCost(&I);
|
|
|
|
// Visit the instruction to analyze its loop cost after unrolling,
|
|
// and if the visitor returns false, include this instruction in the
|
|
// unrolled cost.
|
|
if (!Analyzer.visit(I))
|
|
UnrolledCost += InstCost;
|
|
else {
|
|
DEBUG(dbgs() << " " << I
|
|
<< " would be simplified if loop is unrolled.\n");
|
|
(void)0;
|
|
}
|
|
|
|
// Also track this instructions expected cost when executing the rolled
|
|
// loop form.
|
|
RolledDynamicCost += InstCost;
|
|
|
|
// If unrolled body turns out to be too big, bail out.
|
|
if (UnrolledCost > MaxUnrolledLoopSize) {
|
|
DEBUG(dbgs() << " Exceeded threshold.. exiting.\n"
|
|
<< " UnrolledCost: " << UnrolledCost
|
|
<< ", MaxUnrolledLoopSize: " << MaxUnrolledLoopSize
|
|
<< "\n");
|
|
return None;
|
|
}
|
|
}
|
|
|
|
TerminatorInst *TI = BB->getTerminator();
|
|
|
|
// Add in the live successors by first checking whether we have terminator
|
|
// that may be simplified based on the values simplified by this call.
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
|
|
if (BI->isConditional()) {
|
|
if (Constant *SimpleCond =
|
|
SimplifiedValues.lookup(BI->getCondition())) {
|
|
BasicBlock *Succ = nullptr;
|
|
// Just take the first successor if condition is undef
|
|
if (isa<UndefValue>(SimpleCond))
|
|
Succ = BI->getSuccessor(0);
|
|
else
|
|
Succ = BI->getSuccessor(
|
|
cast<ConstantInt>(SimpleCond)->isZero() ? 1 : 0);
|
|
if (L->contains(Succ))
|
|
BBWorklist.insert(Succ);
|
|
continue;
|
|
}
|
|
}
|
|
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
if (Constant *SimpleCond =
|
|
SimplifiedValues.lookup(SI->getCondition())) {
|
|
BasicBlock *Succ = nullptr;
|
|
// Just take the first successor if condition is undef
|
|
if (isa<UndefValue>(SimpleCond))
|
|
Succ = SI->getSuccessor(0);
|
|
else
|
|
Succ = SI->findCaseValue(cast<ConstantInt>(SimpleCond))
|
|
.getCaseSuccessor();
|
|
if (L->contains(Succ))
|
|
BBWorklist.insert(Succ);
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// Add BB's successors to the worklist.
|
|
for (BasicBlock *Succ : successors(BB))
|
|
if (L->contains(Succ))
|
|
BBWorklist.insert(Succ);
|
|
}
|
|
|
|
// If we found no optimization opportunities on the first iteration, we
|
|
// won't find them on later ones too.
|
|
if (UnrolledCost == RolledDynamicCost) {
|
|
DEBUG(dbgs() << " No opportunities found.. exiting.\n"
|
|
<< " UnrolledCost: " << UnrolledCost << "\n");
|
|
return None;
|
|
}
|
|
}
|
|
DEBUG(dbgs() << "Analysis finished:\n"
|
|
<< "UnrolledCost: " << UnrolledCost << ", "
|
|
<< "RolledDynamicCost: " << RolledDynamicCost << "\n");
|
|
return {{UnrolledCost, RolledDynamicCost}};
|
|
}
|
|
|
|
/// ApproximateLoopSize - Approximate the size of the loop.
|
|
static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls,
|
|
bool &NotDuplicatable,
|
|
const TargetTransformInfo &TTI,
|
|
AssumptionCache *AC) {
|
|
SmallPtrSet<const Value *, 32> EphValues;
|
|
CodeMetrics::collectEphemeralValues(L, AC, EphValues);
|
|
|
|
CodeMetrics Metrics;
|
|
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
|
|
I != E; ++I)
|
|
Metrics.analyzeBasicBlock(*I, TTI, EphValues);
|
|
NumCalls = Metrics.NumInlineCandidates;
|
|
NotDuplicatable = Metrics.notDuplicatable;
|
|
|
|
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. Also, the code using this size may assume
|
|
// that each loop has at least three instructions (likely a conditional
|
|
// branch, a comparison feeding that branch, and some kind of loop increment
|
|
// feeding that comparison instruction).
|
|
LoopSize = std::max(LoopSize, 3u);
|
|
|
|
return LoopSize;
|
|
}
|
|
|
|
// Returns the loop hint metadata node with the given name (for example,
|
|
// "llvm.loop.unroll.count"). If no such metadata node exists, then nullptr is
|
|
// returned.
|
|
static MDNode *GetUnrollMetadataForLoop(const Loop *L, StringRef Name) {
|
|
if (MDNode *LoopID = L->getLoopID())
|
|
return GetUnrollMetadata(LoopID, Name);
|
|
return nullptr;
|
|
}
|
|
|
|
// Returns true if the loop has an unroll(full) pragma.
|
|
static bool HasUnrollFullPragma(const Loop *L) {
|
|
return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.full");
|
|
}
|
|
|
|
// Returns true if the loop has an unroll(enable) pragma. This metadata is used
|
|
// for both "#pragma unroll" and "#pragma clang loop unroll(enable)" directives.
|
|
static bool HasUnrollEnablePragma(const Loop *L) {
|
|
return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.enable");
|
|
}
|
|
|
|
// Returns true if the loop has an unroll(disable) pragma.
|
|
static bool HasUnrollDisablePragma(const Loop *L) {
|
|
return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.disable");
|
|
}
|
|
|
|
// Returns true if the loop has an runtime unroll(disable) pragma.
|
|
static bool HasRuntimeUnrollDisablePragma(const Loop *L) {
|
|
return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.runtime.disable");
|
|
}
|
|
|
|
// If loop has an unroll_count pragma return the (necessarily
|
|
// positive) value from the pragma. Otherwise return 0.
|
|
static unsigned UnrollCountPragmaValue(const Loop *L) {
|
|
MDNode *MD = GetUnrollMetadataForLoop(L, "llvm.loop.unroll.count");
|
|
if (MD) {
|
|
assert(MD->getNumOperands() == 2 &&
|
|
"Unroll count hint metadata should have two operands.");
|
|
unsigned Count =
|
|
mdconst::extract<ConstantInt>(MD->getOperand(1))->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<Metadata *, 4> MDs;
|
|
// Reserve first location for self reference to the LoopID metadata node.
|
|
MDs.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)
|
|
MDs.push_back(LoopID->getOperand(i));
|
|
}
|
|
|
|
// Add unroll(disable) metadata to disable future unrolling.
|
|
LLVMContext &Context = L->getHeader()->getContext();
|
|
SmallVector<Metadata *, 1> DisableOperands;
|
|
DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.disable"));
|
|
MDNode *DisableNode = MDNode::get(Context, DisableOperands);
|
|
MDs.push_back(DisableNode);
|
|
|
|
MDNode *NewLoopID = MDNode::get(Context, MDs);
|
|
// Set operand 0 to refer to the loop id itself.
|
|
NewLoopID->replaceOperandWith(0, NewLoopID);
|
|
L->setLoopID(NewLoopID);
|
|
}
|
|
|
|
bool LoopUnroll::canUnrollCompletely(Loop *L, unsigned Threshold,
|
|
unsigned PercentDynamicCostSavedThreshold,
|
|
unsigned DynamicCostSavingsDiscount,
|
|
uint64_t UnrolledCost,
|
|
uint64_t RolledDynamicCost) {
|
|
|
|
if (Threshold == NoThreshold) {
|
|
DEBUG(dbgs() << " Can fully unroll, because no threshold is set.\n");
|
|
return true;
|
|
}
|
|
|
|
if (UnrolledCost <= Threshold) {
|
|
DEBUG(dbgs() << " Can fully unroll, because unrolled cost: "
|
|
<< UnrolledCost << "<" << Threshold << "\n");
|
|
return true;
|
|
}
|
|
|
|
assert(UnrolledCost && "UnrolledCost can't be 0 at this point.");
|
|
assert(RolledDynamicCost >= UnrolledCost &&
|
|
"Cannot have a higher unrolled cost than a rolled cost!");
|
|
|
|
// Compute the percentage of the dynamic cost in the rolled form that is
|
|
// saved when unrolled. If unrolling dramatically reduces the estimated
|
|
// dynamic cost of the loop, we use a higher threshold to allow more
|
|
// unrolling.
|
|
unsigned PercentDynamicCostSaved =
|
|
(uint64_t)(RolledDynamicCost - UnrolledCost) * 100ull / RolledDynamicCost;
|
|
|
|
if (PercentDynamicCostSaved >= PercentDynamicCostSavedThreshold &&
|
|
(int64_t)UnrolledCost - (int64_t)DynamicCostSavingsDiscount <=
|
|
(int64_t)Threshold) {
|
|
DEBUG(dbgs() << " Can fully unroll, because unrolling will reduce the "
|
|
"expected dynamic cost by " << PercentDynamicCostSaved
|
|
<< "% (threshold: " << PercentDynamicCostSavedThreshold
|
|
<< "%)\n"
|
|
<< " and the unrolled cost (" << UnrolledCost
|
|
<< ") is less than the max threshold ("
|
|
<< DynamicCostSavingsDiscount << ").\n");
|
|
return true;
|
|
}
|
|
|
|
DEBUG(dbgs() << " Too large to fully unroll:\n");
|
|
DEBUG(dbgs() << " Threshold: " << Threshold << "\n");
|
|
DEBUG(dbgs() << " Max threshold: " << DynamicCostSavingsDiscount << "\n");
|
|
DEBUG(dbgs() << " Percent cost saved threshold: "
|
|
<< PercentDynamicCostSavedThreshold << "%\n");
|
|
DEBUG(dbgs() << " Unrolled cost: " << UnrolledCost << "\n");
|
|
DEBUG(dbgs() << " Rolled dynamic cost: " << RolledDynamicCost << "\n");
|
|
DEBUG(dbgs() << " Percent cost saved: " << PercentDynamicCostSaved
|
|
<< "\n");
|
|
return false;
|
|
}
|
|
|
|
unsigned LoopUnroll::selectUnrollCount(
|
|
const Loop *L, unsigned TripCount, bool PragmaFullUnroll,
|
|
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 precedence.
|
|
if (Count == 0) {
|
|
if (PragmaCount) {
|
|
Count = PragmaCount;
|
|
} else if (PragmaFullUnroll) {
|
|
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;
|
|
|
|
Function &F = *L->getHeader()->getParent();
|
|
|
|
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
|
|
LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
|
|
ScalarEvolution *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
|
|
const TargetTransformInfo &TTI =
|
|
getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
|
|
auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
|
|
|
|
BasicBlock *Header = L->getHeader();
|
|
DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName()
|
|
<< "] Loop %" << Header->getName() << "\n");
|
|
|
|
if (HasUnrollDisablePragma(L)) {
|
|
return false;
|
|
}
|
|
bool PragmaFullUnroll = HasUnrollFullPragma(L);
|
|
bool PragmaEnableUnroll = HasUnrollEnablePragma(L);
|
|
unsigned PragmaCount = UnrollCountPragmaValue(L);
|
|
bool HasPragma = PragmaFullUnroll || PragmaEnableUnroll || PragmaCount > 0;
|
|
|
|
TargetTransformInfo::UnrollingPreferences UP;
|
|
getUnrollingPreferences(L, TTI, UP);
|
|
|
|
// Find trip count and trip multiple if count is not available
|
|
unsigned TripCount = 0;
|
|
unsigned TripMultiple = 1;
|
|
// If there are multiple exiting blocks but one of them is the latch, use the
|
|
// latch for the trip count estimation. Otherwise insist on a single exiting
|
|
// block for the trip count estimation.
|
|
BasicBlock *ExitingBlock = L->getLoopLatch();
|
|
if (!ExitingBlock || !L->isLoopExiting(ExitingBlock))
|
|
ExitingBlock = L->getExitingBlock();
|
|
if (ExitingBlock) {
|
|
TripCount = SE->getSmallConstantTripCount(L, ExitingBlock);
|
|
TripMultiple = SE->getSmallConstantTripMultiple(L, ExitingBlock);
|
|
}
|
|
|
|
// Select an initial unroll count. This may be reduced later based
|
|
// on size thresholds.
|
|
bool CountSetExplicitly;
|
|
unsigned Count = selectUnrollCount(L, TripCount, PragmaFullUnroll,
|
|
PragmaCount, UP, CountSetExplicitly);
|
|
|
|
unsigned NumInlineCandidates;
|
|
bool notDuplicatable;
|
|
unsigned LoopSize =
|
|
ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI, &AC);
|
|
DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n");
|
|
|
|
// When computing the unrolled size, note that the conditional branch on the
|
|
// backedge and the comparison feeding it are not replicated like the rest of
|
|
// the loop body (which is why 2 is subtracted).
|
|
uint64_t UnrolledSize = (uint64_t)(LoopSize-2) * Count + 2;
|
|
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;
|
|
}
|
|
|
|
unsigned Threshold, PartialThreshold;
|
|
unsigned PercentDynamicCostSavedThreshold;
|
|
unsigned DynamicCostSavingsDiscount;
|
|
// Only use the high pragma threshold when we have a target unroll factor such
|
|
// as with "#pragma unroll N" or a pragma indicating full unrolling and the
|
|
// trip count is known. Otherwise we rely on the standard threshold to
|
|
// heuristically select a reasonable unroll count.
|
|
bool UsePragmaThreshold =
|
|
PragmaCount > 0 ||
|
|
((PragmaFullUnroll || PragmaEnableUnroll) && TripCount != 0);
|
|
|
|
selectThresholds(L, UsePragmaThreshold, UP, Threshold, PartialThreshold,
|
|
PercentDynamicCostSavedThreshold,
|
|
DynamicCostSavingsDiscount);
|
|
|
|
// 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) {
|
|
Unrolling = Partial;
|
|
// If the loop is really small, we don't need to run an expensive analysis.
|
|
if (canUnrollCompletely(L, Threshold, 100, DynamicCostSavingsDiscount,
|
|
UnrolledSize, UnrolledSize)) {
|
|
Unrolling = Full;
|
|
} else {
|
|
// The loop isn't that small, but we still can fully unroll it if that
|
|
// helps to remove a significant number of instructions.
|
|
// To check that, run additional analysis on the loop.
|
|
if (Optional<EstimatedUnrollCost> Cost =
|
|
analyzeLoopUnrollCost(L, TripCount, DT, *SE, TTI,
|
|
Threshold + DynamicCostSavingsDiscount))
|
|
if (canUnrollCompletely(L, Threshold, PercentDynamicCostSavedThreshold,
|
|
DynamicCostSavingsDiscount, Cost->UnrolledCost,
|
|
Cost->RolledDynamicCost)) {
|
|
Unrolling = Full;
|
|
}
|
|
}
|
|
} else if (TripCount && Count < TripCount) {
|
|
Unrolling = Partial;
|
|
} else {
|
|
Unrolling = Runtime;
|
|
}
|
|
|
|
// Reduce count based on the type of unrolling and the threshold values.
|
|
unsigned OriginalCount = Count;
|
|
bool AllowRuntime = PragmaEnableUnroll || (PragmaCount > 0) ||
|
|
(UserRuntime ? CurrentRuntime : UP.Runtime);
|
|
// Don't unroll a runtime trip count loop with unroll full pragma.
|
|
if (HasRuntimeUnrollDisablePragma(L) || PragmaFullUnroll) {
|
|
AllowRuntime = false;
|
|
}
|
|
if (Unrolling == Partial) {
|
|
bool AllowPartial = PragmaEnableUnroll ||
|
|
(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 (PartialThreshold != NoThreshold && UnrolledSize > PartialThreshold) {
|
|
// Reduce unroll count to be modulo of TripCount for partial unrolling.
|
|
Count = (std::max(PartialThreshold, 3u)-2) / (LoopSize-2);
|
|
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;
|
|
}
|
|
// 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-2) * Count + 2;
|
|
}
|
|
if (Count > UP.MaxCount)
|
|
Count = UP.MaxCount;
|
|
DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n");
|
|
}
|
|
|
|
if (HasPragma) {
|
|
if (PragmaCount != 0)
|
|
// If loop has an unroll count pragma 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 ((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.");
|
|
} else if (PragmaFullUnroll && !TripCount) {
|
|
emitOptimizationRemarkMissed(
|
|
Ctx, DEBUG_TYPE, *F, LoopLoc,
|
|
"Unable to fully unroll loop as directed by unroll(full) pragma "
|
|
"because loop has a runtime trip count.");
|
|
} else if (PragmaEnableUnroll && Count != TripCount && Count < 2) {
|
|
emitOptimizationRemarkMissed(
|
|
Ctx, DEBUG_TYPE, *F, LoopLoc,
|
|
"Unable to unroll loop as directed by unroll(enable) pragma because "
|
|
"unrolled size is too large.");
|
|
} else if ((PragmaFullUnroll || PragmaEnableUnroll) && TripCount &&
|
|
Count != TripCount) {
|
|
emitOptimizationRemarkMissed(
|
|
Ctx, DEBUG_TYPE, *F, LoopLoc,
|
|
"Unable to fully unroll loop as directed by unroll 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, AllowRuntime, UP.AllowExpensiveTripCount,
|
|
TripMultiple, LI, this, &LPM, &AC))
|
|
return false;
|
|
|
|
return true;
|
|
}
|