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The issues with the new unroll analyzer are more fundamental than code cleanup, algorithm, or data structure changes. I've sent an email to the original commit thread with details and a proposal for how to redesign things. I'm disabling this for now so that we don't spend time debugging issues with it in its current state. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229064 91177308-0d34-0410-b5e6-96231b3b80d8
885 lines
35 KiB
C++
885 lines
35 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/AssumptionCache.h"
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#include "llvm/Analysis/CodeMetrics.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/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 "llvm/IR/InstVisitor.h"
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#include "llvm/Analysis/InstructionSimplify.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 cut-off point for automatic loop unrolling"));
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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> UnrollMinPercentOfOptimized(
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"unroll-percent-of-optimized-for-complete-unroll", cl::init(20), cl::Hidden,
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cl::desc("If complete unrolling could trigger further optimizations, and, "
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"by that, remove the given percent of instructions, perform the "
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"complete unroll even if it's beyond the threshold"));
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static cl::opt<unsigned> UnrollAbsoluteThreshold(
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"unroll-absolute-threshold", cl::init(2000), cl::Hidden,
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cl::desc("Don't unroll if the unrolled size is bigger than this threshold,"
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" even if we can remove big portion of instructions later."));
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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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CurrentAbsoluteThreshold = UnrollAbsoluteThreshold;
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CurrentMinPercentOfOptimized = UnrollMinPercentOfOptimized;
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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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UserAbsoluteThreshold = (UnrollAbsoluteThreshold.getNumOccurrences() > 0);
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UserPercentOfOptimized =
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(UnrollMinPercentOfOptimized.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 CurrentAbsoluteThreshold;
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unsigned CurrentMinPercentOfOptimized;
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bool CurrentAllowPartial;
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bool CurrentRuntime;
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bool UserCount; // CurrentCount is user-specified.
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bool UserThreshold; // CurrentThreshold is user-specified.
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bool UserAbsoluteThreshold; // CurrentAbsoluteThreshold is
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// user-specified.
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bool UserPercentOfOptimized; // CurrentMinPercentOfOptimized is
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// user-specified.
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bool UserAllowPartial; // CurrentAllowPartial is user-specified.
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bool UserRuntime; // CurrentRuntime is user-specified.
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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<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<ScalarEvolution>();
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AU.addPreserved<ScalarEvolution>();
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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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}
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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.AbsoluteThreshold = CurrentAbsoluteThreshold;
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UP.MinPercentOfOptimized = CurrentMinPercentOfOptimized;
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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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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 HasPragma,
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const TargetTransformInfo::UnrollingPreferences &UP,
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unsigned &Threshold, unsigned &PartialThreshold,
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unsigned NumberOfOptimizedInstructions) {
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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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// If we are allowed to completely unroll if we can remove M% of
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// instructions, and we know that with complete unrolling we'll be able
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// to kill N instructions, then we can afford to completely unroll loops
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// with unrolled size up to N*100/M.
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// Adjust the threshold according to that:
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unsigned PercentOfOptimizedForCompleteUnroll =
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UserPercentOfOptimized ? CurrentMinPercentOfOptimized
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: UP.MinPercentOfOptimized;
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unsigned AbsoluteThreshold = UserAbsoluteThreshold
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? CurrentAbsoluteThreshold
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: UP.AbsoluteThreshold;
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if (PercentOfOptimizedForCompleteUnroll)
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Threshold = std::max<unsigned>(Threshold,
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NumberOfOptimizedInstructions * 100 /
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PercentOfOptimizedForCompleteUnroll);
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// But don't allow unrolling loops bigger than absolute threshold.
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Threshold = std::min<unsigned>(Threshold, AbsoluteThreshold);
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PartialThreshold = UserThreshold ? CurrentThreshold : UP.PartialThreshold;
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if (!UserThreshold &&
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L->getHeader()->getParent()->getAttributes().
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hasAttribute(AttributeSet::FunctionIndex,
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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 (HasPragma) {
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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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};
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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(LoopInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
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INITIALIZE_PASS_DEPENDENCY(LCSSA)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
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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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static bool isLoadFromConstantInitializer(Value *V) {
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if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
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if (GV->isConstant() && GV->hasDefinitiveInitializer())
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return GV->getInitializer();
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return false;
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}
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struct FindConstantPointers {
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bool LoadCanBeConstantFolded;
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bool IndexIsConstant;
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APInt Step;
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APInt StartValue;
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Value *BaseAddress;
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const Loop *L;
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ScalarEvolution &SE;
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FindConstantPointers(const Loop *loop, ScalarEvolution &SE)
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: LoadCanBeConstantFolded(true), IndexIsConstant(true), L(loop), SE(SE) {}
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bool follow(const SCEV *S) {
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if (const SCEVUnknown *SC = dyn_cast<SCEVUnknown>(S)) {
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// We've reached the leaf node of SCEV, it's most probably just a
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// variable. Now it's time to see if it corresponds to a global constant
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// global (in which case we can eliminate the load), or not.
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BaseAddress = SC->getValue();
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LoadCanBeConstantFolded =
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IndexIsConstant && isLoadFromConstantInitializer(BaseAddress);
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return false;
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}
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if (isa<SCEVConstant>(S))
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return true;
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if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
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// If the current SCEV expression is AddRec, and its loop isn't the loop
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// we are about to unroll, then we won't get a constant address after
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// unrolling, and thus, won't be able to eliminate the load.
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if (AR->getLoop() != L)
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return IndexIsConstant = false;
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// If the step isn't constant, we won't get constant addresses in unrolled
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// version. Bail out.
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if (const SCEVConstant *StepSE =
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dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
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Step = StepSE->getValue()->getValue();
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else
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return IndexIsConstant = false;
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return IndexIsConstant;
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}
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// If Result is true, continue traversal.
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// Otherwise, we have found something that prevents us from (possible) load
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// elimination.
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return IndexIsConstant;
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}
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bool isDone() const { return !IndexIsConstant; }
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};
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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 UnrollAnalyzer : public InstVisitor<UnrollAnalyzer, bool> {
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typedef InstVisitor<UnrollAnalyzer, bool> Base;
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friend class InstVisitor<UnrollAnalyzer, bool>;
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const Loop *L;
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unsigned TripCount;
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ScalarEvolution &SE;
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const TargetTransformInfo &TTI;
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DenseMap<Value *, Constant *> SimplifiedValues;
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DenseMap<LoadInst *, Value *> LoadBaseAddresses;
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SmallPtrSet<Instruction *, 32> CountedInstructions;
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/// \brief Count the number of optimized instructions.
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unsigned NumberOfOptimizedInstructions;
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// Provide base case for our instruction visit.
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bool visitInstruction(Instruction &I) { return false; };
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// TODO: We should also visit ICmp, FCmp, GetElementPtr, Trunc, ZExt, SExt,
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// FPTrunc, FPExt, FPToUI, FPToSI, UIToFP, SIToFP, BitCast, Select,
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// ExtractElement, InsertElement, ShuffleVector, ExtractValue, InsertValue.
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//
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// Probaly it's worth to hoist the code for estimating the simplifications
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// effects to a separate class, since we have a very similar code in
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// 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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if (auto FI = dyn_cast<FPMathOperator>(&I))
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SimpleV =
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SimplifyFPBinOp(I.getOpcode(), LHS, RHS, FI->getFastMathFlags());
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else
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SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS);
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if (SimpleV && CountedInstructions.insert(&I).second)
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NumberOfOptimizedInstructions += TTI.getUserCost(&I);
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if (Constant *C = dyn_cast_or_null<Constant>(SimpleV)) {
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SimplifiedValues[&I] = C;
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return true;
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}
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return false;
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}
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Constant *computeLoadValue(LoadInst *LI, unsigned Iteration) {
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if (!LI)
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return nullptr;
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Value *BaseAddr = LoadBaseAddresses[LI];
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if (!BaseAddr)
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return nullptr;
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auto GV = dyn_cast<GlobalVariable>(BaseAddr);
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if (!GV)
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return nullptr;
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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 nullptr;
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const SCEV *BaseAddrSE = SE.getSCEV(BaseAddr);
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const SCEV *S = SE.getSCEV(LI->getPointerOperand());
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const SCEV *OffSE = SE.getMinusSCEV(S, BaseAddrSE);
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APInt StepC, StartC;
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const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(OffSE);
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if (!AR)
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return nullptr;
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if (const SCEVConstant *StepSE =
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dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
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StepC = StepSE->getValue()->getValue();
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else
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return nullptr;
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if (const SCEVConstant *StartSE = dyn_cast<SCEVConstant>(AR->getStart()))
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StartC = StartSE->getValue()->getValue();
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else
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return nullptr;
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unsigned ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U;
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unsigned Start = StartC.getLimitedValue();
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unsigned Step = StepC.getLimitedValue();
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unsigned Index = (Start + Step * Iteration) / ElemSize;
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if (Index >= CDS->getNumElements())
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return nullptr;
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Constant *CV = CDS->getElementAsConstant(Index);
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return CV;
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}
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public:
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UnrollAnalyzer(const Loop *L, unsigned TripCount, ScalarEvolution &SE,
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const TargetTransformInfo &TTI)
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: L(L), TripCount(TripCount), SE(SE), TTI(TTI),
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NumberOfOptimizedInstructions(0) {}
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// Visit all loads the loop L, and for those that, after complete loop
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// unrolling, would have a constant address and it will point to a known
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// constant initializer, record its base address for future use. It is used
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// when we estimate number of potentially simplified instructions.
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void findConstFoldableLoads() {
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for (auto BB : L->getBlocks()) {
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for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
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if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
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if (!LI->isSimple())
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continue;
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Value *AddrOp = LI->getPointerOperand();
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const SCEV *S = SE.getSCEV(AddrOp);
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FindConstantPointers Visitor(L, SE);
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SCEVTraversal<FindConstantPointers> T(Visitor);
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T.visitAll(S);
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if (Visitor.IndexIsConstant && Visitor.LoadCanBeConstantFolded) {
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LoadBaseAddresses[LI] = Visitor.BaseAddress;
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}
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}
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}
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}
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}
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// Given a list of loads that could be constant-folded (LoadBaseAddresses),
|
|
// estimate number of optimized instructions after substituting the concrete
|
|
// values for the given Iteration. Also track how many instructions become
|
|
// dead through this process.
|
|
unsigned estimateNumberOfOptimizedInstructions(unsigned Iteration) {
|
|
// We keep a set vector for the worklist so that we don't wast space in the
|
|
// worklist queuing up the same instruction repeatedly. This can happen due
|
|
// to multiple operands being the same instruction or due to the same
|
|
// instruction being an operand of lots of things that end up dead or
|
|
// simplified.
|
|
SmallSetVector<Instruction *, 8> Worklist;
|
|
|
|
// Clear the simplified values and counts for this iteration.
|
|
SimplifiedValues.clear();
|
|
CountedInstructions.clear();
|
|
NumberOfOptimizedInstructions = 0;
|
|
|
|
// We start by adding all loads to the worklist.
|
|
for (auto &LoadDescr : LoadBaseAddresses) {
|
|
LoadInst *LI = LoadDescr.first;
|
|
SimplifiedValues[LI] = computeLoadValue(LI, Iteration);
|
|
if (CountedInstructions.insert(LI).second)
|
|
NumberOfOptimizedInstructions += TTI.getUserCost(LI);
|
|
|
|
for (User *U : LI->users())
|
|
Worklist.insert(cast<Instruction>(U));
|
|
}
|
|
|
|
// And then we try to simplify every user of every instruction from the
|
|
// worklist. If we do simplify a user, add it to the worklist to process
|
|
// its users as well.
|
|
while (!Worklist.empty()) {
|
|
Instruction *I = Worklist.pop_back_val();
|
|
if (!L->contains(I))
|
|
continue;
|
|
if (!visit(I))
|
|
continue;
|
|
for (User *U : I->users())
|
|
Worklist.insert(cast<Instruction>(U));
|
|
}
|
|
|
|
// Now that we know the potentially simplifed instructions, estimate number
|
|
// of instructions that would become dead if we do perform the
|
|
// simplification.
|
|
|
|
// The dead instructions are held in a separate set. This is used to
|
|
// prevent us from re-examining instructions and make sure we only count
|
|
// the benifit once. The worklist's internal set handles insertion
|
|
// deduplication.
|
|
SmallPtrSet<Instruction *, 16> DeadInstructions;
|
|
|
|
// Lambda to enque operands onto the worklist.
|
|
auto EnqueueOperands = [&](Instruction &I) {
|
|
for (auto *Op : I.operand_values())
|
|
if (auto *OpI = dyn_cast<Instruction>(Op))
|
|
if (!OpI->use_empty())
|
|
Worklist.insert(OpI);
|
|
};
|
|
|
|
// Start by initializing worklist with simplified instructions.
|
|
for (auto &FoldedKeyValue : SimplifiedValues)
|
|
if (auto *FoldedInst = dyn_cast<Instruction>(FoldedKeyValue.first)) {
|
|
DeadInstructions.insert(FoldedInst);
|
|
|
|
// Add each instruction operand of this dead instruction to the
|
|
// worklist.
|
|
EnqueueOperands(*FoldedInst);
|
|
}
|
|
|
|
// If a definition of an insn is only used by simplified or dead
|
|
// instructions, it's also dead. Check defs of all instructions from the
|
|
// worklist.
|
|
while (!Worklist.empty()) {
|
|
Instruction *I = Worklist.pop_back_val();
|
|
if (!L->contains(I))
|
|
continue;
|
|
if (DeadInstructions.count(I))
|
|
continue;
|
|
|
|
if (std::all_of(I->user_begin(), I->user_end(), [&](User *U) {
|
|
return DeadInstructions.count(cast<Instruction>(U));
|
|
})) {
|
|
NumberOfOptimizedInstructions += TTI.getUserCost(I);
|
|
DeadInstructions.insert(I);
|
|
EnqueueOperands(*I);
|
|
}
|
|
}
|
|
return NumberOfOptimizedInstructions;
|
|
}
|
|
};
|
|
|
|
// 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 effect and returns the number of
|
|
// instructions, that potentially might be optimized away.
|
|
static unsigned
|
|
approximateNumberOfOptimizedInstructions(const Loop *L, ScalarEvolution &SE,
|
|
unsigned TripCount,
|
|
const TargetTransformInfo &TTI) {
|
|
if (!TripCount || !UnrollMaxIterationsCountToAnalyze)
|
|
return 0;
|
|
|
|
UnrollAnalyzer UA(L, TripCount, SE, TTI);
|
|
UA.findConstFoldableLoads();
|
|
|
|
// Estimate number of instructions, that could be simplified if we replace a
|
|
// load with the corresponding constant. Since the same load will take
|
|
// different values on different iterations, we have to go through all loop's
|
|
// iterations here. To limit ourselves here, we check only first N
|
|
// iterations, and then scale the found number, if necessary.
|
|
unsigned IterationsNumberForEstimate =
|
|
std::min<unsigned>(UnrollMaxIterationsCountToAnalyze, TripCount);
|
|
unsigned NumberOfOptimizedInstructions = 0;
|
|
for (unsigned i = 0; i < IterationsNumberForEstimate; ++i)
|
|
NumberOfOptimizedInstructions +=
|
|
UA.estimateNumberOfOptimizedInstructions(i);
|
|
|
|
NumberOfOptimizedInstructions *= TripCount / IterationsNumberForEstimate;
|
|
|
|
return NumberOfOptimizedInstructions;
|
|
}
|
|
|
|
/// 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(disable) pragma.
|
|
static bool HasUnrollDisablePragma(const Loop *L) {
|
|
return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.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);
|
|
}
|
|
|
|
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 precendence.
|
|
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();
|
|
|
|
LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
|
|
ScalarEvolution *SE = &getAnalysis<ScalarEvolution>();
|
|
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);
|
|
unsigned PragmaCount = UnrollCountPragmaValue(L);
|
|
bool HasPragma = PragmaFullUnroll || 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 NumberOfOptimizedInstructions =
|
|
approximateNumberOfOptimizedInstructions(L, *SE, TripCount, TTI);
|
|
DEBUG(dbgs() << " Complete unrolling could save: "
|
|
<< NumberOfOptimizedInstructions << "\n");
|
|
|
|
unsigned Threshold, PartialThreshold;
|
|
selectThresholds(L, HasPragma, UP, Threshold, PartialThreshold,
|
|
NumberOfOptimizedInstructions);
|
|
|
|
// 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;
|
|
}
|
|
|
|
// 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 (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 (PragmaFullUnroll && PragmaCount == 0) {
|
|
if (TripCount && Count != TripCount) {
|
|
emitOptimizationRemarkMissed(
|
|
Ctx, DEBUG_TYPE, *F, LoopLoc,
|
|
"Unable to fully unroll loop as directed by unroll(full) 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(full) pragma "
|
|
"because loop has a runtime trip count.");
|
|
}
|
|
} 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, AllowRuntime, TripMultiple, LI, this,
|
|
&LPM, &AC))
|
|
return false;
|
|
|
|
return true;
|
|
}
|