forked from OSchip/llvm-project
647 lines
26 KiB
C++
647 lines
26 KiB
C++
//===- UnrollLoopPeel.cpp - Loop peeling utilities ------------------------===//
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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 file implements some loop unrolling utilities for peeling loops
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// with dynamically inferred (from PGO) trip counts. See LoopUnroll.cpp for
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// unrolling loops with compile-time constant trip counts.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/Optional.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/LoopIterator.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/BasicBlock.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/InstrTypes.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/MDBuilder.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/IR/PatternMatch.h"
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#include "llvm/Support/Casting.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/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include "llvm/Transforms/Utils/LoopSimplify.h"
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#include "llvm/Transforms/Utils/LoopUtils.h"
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#include "llvm/Transforms/Utils/UnrollLoop.h"
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#include "llvm/Transforms/Utils/ValueMapper.h"
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#include <algorithm>
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#include <cassert>
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#include <cstdint>
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#include <limits>
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using namespace llvm;
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using namespace llvm::PatternMatch;
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#define DEBUG_TYPE "loop-unroll"
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STATISTIC(NumPeeled, "Number of loops peeled");
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static cl::opt<unsigned> UnrollPeelMaxCount(
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"unroll-peel-max-count", cl::init(7), cl::Hidden,
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cl::desc("Max average trip count which will cause loop peeling."));
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static cl::opt<unsigned> UnrollForcePeelCount(
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"unroll-force-peel-count", cl::init(0), cl::Hidden,
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cl::desc("Force a peel count regardless of profiling information."));
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// Designates that a Phi is estimated to become invariant after an "infinite"
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// number of loop iterations (i.e. only may become an invariant if the loop is
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// fully unrolled).
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static const unsigned InfiniteIterationsToInvariance =
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std::numeric_limits<unsigned>::max();
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// Check whether we are capable of peeling this loop.
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static bool canPeel(Loop *L) {
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// Make sure the loop is in simplified form
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if (!L->isLoopSimplifyForm())
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return false;
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// Only peel loops that contain a single exit
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if (!L->getExitingBlock() || !L->getUniqueExitBlock())
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return false;
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// Don't try to peel loops where the latch is not the exiting block.
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// This can be an indication of two different things:
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// 1) The loop is not rotated.
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// 2) The loop contains irreducible control flow that involves the latch.
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if (L->getLoopLatch() != L->getExitingBlock())
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return false;
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return true;
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}
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// This function calculates the number of iterations after which the given Phi
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// becomes an invariant. The pre-calculated values are memorized in the map. The
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// function (shortcut is I) is calculated according to the following definition:
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// Given %x = phi <Inputs from above the loop>, ..., [%y, %back.edge].
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// If %y is a loop invariant, then I(%x) = 1.
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// If %y is a Phi from the loop header, I(%x) = I(%y) + 1.
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// Otherwise, I(%x) is infinite.
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// TODO: Actually if %y is an expression that depends only on Phi %z and some
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// loop invariants, we can estimate I(%x) = I(%z) + 1. The example
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// looks like:
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// %x = phi(0, %a), <-- becomes invariant starting from 3rd iteration.
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// %y = phi(0, 5),
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// %a = %y + 1.
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static unsigned calculateIterationsToInvariance(
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PHINode *Phi, Loop *L, BasicBlock *BackEdge,
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SmallDenseMap<PHINode *, unsigned> &IterationsToInvariance) {
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assert(Phi->getParent() == L->getHeader() &&
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"Non-loop Phi should not be checked for turning into invariant.");
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assert(BackEdge == L->getLoopLatch() && "Wrong latch?");
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// If we already know the answer, take it from the map.
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auto I = IterationsToInvariance.find(Phi);
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if (I != IterationsToInvariance.end())
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return I->second;
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// Otherwise we need to analyze the input from the back edge.
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Value *Input = Phi->getIncomingValueForBlock(BackEdge);
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// Place infinity to map to avoid infinite recursion for cycled Phis. Such
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// cycles can never stop on an invariant.
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IterationsToInvariance[Phi] = InfiniteIterationsToInvariance;
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unsigned ToInvariance = InfiniteIterationsToInvariance;
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if (L->isLoopInvariant(Input))
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ToInvariance = 1u;
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else if (PHINode *IncPhi = dyn_cast<PHINode>(Input)) {
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// Only consider Phis in header block.
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if (IncPhi->getParent() != L->getHeader())
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return InfiniteIterationsToInvariance;
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// If the input becomes an invariant after X iterations, then our Phi
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// becomes an invariant after X + 1 iterations.
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unsigned InputToInvariance = calculateIterationsToInvariance(
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IncPhi, L, BackEdge, IterationsToInvariance);
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if (InputToInvariance != InfiniteIterationsToInvariance)
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ToInvariance = InputToInvariance + 1u;
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}
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// If we found that this Phi lies in an invariant chain, update the map.
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if (ToInvariance != InfiniteIterationsToInvariance)
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IterationsToInvariance[Phi] = ToInvariance;
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return ToInvariance;
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}
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// Return the number of iterations to peel off that make conditions in the
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// body true/false. For example, if we peel 2 iterations off the loop below,
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// the condition i < 2 can be evaluated at compile time.
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// for (i = 0; i < n; i++)
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// if (i < 2)
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// ..
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// else
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// ..
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// }
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static unsigned countToEliminateCompares(Loop &L, unsigned MaxPeelCount,
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ScalarEvolution &SE) {
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assert(L.isLoopSimplifyForm() && "Loop needs to be in loop simplify form");
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unsigned DesiredPeelCount = 0;
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for (auto *BB : L.blocks()) {
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auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
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if (!BI || BI->isUnconditional())
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continue;
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// Ignore loop exit condition.
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if (L.getLoopLatch() == BB)
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continue;
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Value *Condition = BI->getCondition();
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Value *LeftVal, *RightVal;
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CmpInst::Predicate Pred;
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if (!match(Condition, m_ICmp(Pred, m_Value(LeftVal), m_Value(RightVal))))
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continue;
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const SCEV *LeftSCEV = SE.getSCEV(LeftVal);
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const SCEV *RightSCEV = SE.getSCEV(RightVal);
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// Do not consider predicates that are known to be true or false
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// independently of the loop iteration.
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if (SE.isKnownPredicate(Pred, LeftSCEV, RightSCEV) ||
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SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), LeftSCEV,
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RightSCEV))
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continue;
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// Check if we have a condition with one AddRec and one non AddRec
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// expression. Normalize LeftSCEV to be the AddRec.
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if (!isa<SCEVAddRecExpr>(LeftSCEV)) {
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if (isa<SCEVAddRecExpr>(RightSCEV)) {
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std::swap(LeftSCEV, RightSCEV);
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Pred = ICmpInst::getSwappedPredicate(Pred);
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} else
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continue;
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}
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const SCEVAddRecExpr *LeftAR = cast<SCEVAddRecExpr>(LeftSCEV);
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// Avoid huge SCEV computations in the loop below and make sure we only
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// consider AddRecs of the loop we are trying to peel.
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if (!LeftAR->isAffine() || LeftAR->getLoop() != &L)
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continue;
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// Check if extending DesiredPeelCount lets us evaluate Pred.
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const SCEV *IterVal = LeftAR->evaluateAtIteration(
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SE.getConstant(LeftSCEV->getType(), DesiredPeelCount), SE);
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// If the original condition is not known, get the negated predicate
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// (which holds on the else branch) and check if it is known. This allows
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// us to peel of iterations that make the original condition false.
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if (!SE.isKnownPredicate(Pred, IterVal, RightSCEV))
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Pred = ICmpInst::getInversePredicate(Pred);
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const SCEV *Step = LeftAR->getStepRecurrence(SE);
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while (DesiredPeelCount < MaxPeelCount &&
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SE.isKnownPredicate(Pred, IterVal, RightSCEV)) {
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IterVal = SE.getAddExpr(IterVal, Step);
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DesiredPeelCount++;
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}
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}
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return DesiredPeelCount;
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}
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// Return the number of iterations we want to peel off.
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void llvm::computePeelCount(Loop *L, unsigned LoopSize,
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TargetTransformInfo::UnrollingPreferences &UP,
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unsigned &TripCount, ScalarEvolution &SE) {
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assert(LoopSize > 0 && "Zero loop size is not allowed!");
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UP.PeelCount = 0;
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if (!canPeel(L))
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return;
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// Only try to peel innermost loops.
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if (!L->empty())
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return;
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// Here we try to get rid of Phis which become invariants after 1, 2, ..., N
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// iterations of the loop. For this we compute the number for iterations after
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// which every Phi is guaranteed to become an invariant, and try to peel the
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// maximum number of iterations among these values, thus turning all those
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// Phis into invariants.
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// First, check that we can peel at least one iteration.
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if (2 * LoopSize <= UP.Threshold && UnrollPeelMaxCount > 0) {
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// Store the pre-calculated values here.
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SmallDenseMap<PHINode *, unsigned> IterationsToInvariance;
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// Now go through all Phis to calculate their the number of iterations they
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// need to become invariants.
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unsigned DesiredPeelCount = 0;
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BasicBlock *BackEdge = L->getLoopLatch();
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assert(BackEdge && "Loop is not in simplified form?");
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for (auto BI = L->getHeader()->begin(); isa<PHINode>(&*BI); ++BI) {
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PHINode *Phi = cast<PHINode>(&*BI);
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unsigned ToInvariance = calculateIterationsToInvariance(
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Phi, L, BackEdge, IterationsToInvariance);
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if (ToInvariance != InfiniteIterationsToInvariance)
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DesiredPeelCount = std::max(DesiredPeelCount, ToInvariance);
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}
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// Pay respect to limitations implied by loop size and the max peel count.
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unsigned MaxPeelCount = UnrollPeelMaxCount;
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MaxPeelCount = std::min(MaxPeelCount, UP.Threshold / LoopSize - 1);
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DesiredPeelCount = std::max(DesiredPeelCount,
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countToEliminateCompares(*L, MaxPeelCount, SE));
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if (DesiredPeelCount > 0) {
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DesiredPeelCount = std::min(DesiredPeelCount, MaxPeelCount);
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// Consider max peel count limitation.
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assert(DesiredPeelCount > 0 && "Wrong loop size estimation?");
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DEBUG(dbgs() << "Peel " << DesiredPeelCount << " iteration(s) to turn"
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<< " some Phis into invariants.\n");
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UP.PeelCount = DesiredPeelCount;
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return;
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}
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}
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// Bail if we know the statically calculated trip count.
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// In this case we rather prefer partial unrolling.
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if (TripCount)
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return;
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// If the user provided a peel count, use that.
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bool UserPeelCount = UnrollForcePeelCount.getNumOccurrences() > 0;
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if (UserPeelCount) {
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DEBUG(dbgs() << "Force-peeling first " << UnrollForcePeelCount
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<< " iterations.\n");
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UP.PeelCount = UnrollForcePeelCount;
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return;
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}
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// If we don't know the trip count, but have reason to believe the average
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// trip count is low, peeling should be beneficial, since we will usually
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// hit the peeled section.
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// We only do this in the presence of profile information, since otherwise
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// our estimates of the trip count are not reliable enough.
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if (UP.AllowPeeling && L->getHeader()->getParent()->hasProfileData()) {
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Optional<unsigned> PeelCount = getLoopEstimatedTripCount(L);
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if (!PeelCount)
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return;
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DEBUG(dbgs() << "Profile-based estimated trip count is " << *PeelCount
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<< "\n");
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if (*PeelCount) {
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if ((*PeelCount <= UnrollPeelMaxCount) &&
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(LoopSize * (*PeelCount + 1) <= UP.Threshold)) {
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DEBUG(dbgs() << "Peeling first " << *PeelCount << " iterations.\n");
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UP.PeelCount = *PeelCount;
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return;
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}
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DEBUG(dbgs() << "Requested peel count: " << *PeelCount << "\n");
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DEBUG(dbgs() << "Max peel count: " << UnrollPeelMaxCount << "\n");
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DEBUG(dbgs() << "Peel cost: " << LoopSize * (*PeelCount + 1) << "\n");
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DEBUG(dbgs() << "Max peel cost: " << UP.Threshold << "\n");
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}
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}
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}
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/// \brief Update the branch weights of the latch of a peeled-off loop
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/// iteration.
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/// This sets the branch weights for the latch of the recently peeled off loop
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/// iteration correctly.
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/// Our goal is to make sure that:
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/// a) The total weight of all the copies of the loop body is preserved.
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/// b) The total weight of the loop exit is preserved.
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/// c) The body weight is reasonably distributed between the peeled iterations.
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///
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/// \param Header The copy of the header block that belongs to next iteration.
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/// \param LatchBR The copy of the latch branch that belongs to this iteration.
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/// \param IterNumber The serial number of the iteration that was just
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/// peeled off.
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/// \param AvgIters The average number of iterations we expect the loop to have.
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/// \param[in,out] PeeledHeaderWeight The total number of dynamic loop
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/// iterations that are unaccounted for. As an input, it represents the number
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/// of times we expect to enter the header of the iteration currently being
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/// peeled off. The output is the number of times we expect to enter the
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/// header of the next iteration.
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static void updateBranchWeights(BasicBlock *Header, BranchInst *LatchBR,
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unsigned IterNumber, unsigned AvgIters,
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uint64_t &PeeledHeaderWeight) {
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// FIXME: Pick a more realistic distribution.
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// Currently the proportion of weight we assign to the fall-through
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// side of the branch drops linearly with the iteration number, and we use
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// a 0.9 fudge factor to make the drop-off less sharp...
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if (PeeledHeaderWeight) {
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uint64_t FallThruWeight =
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PeeledHeaderWeight * ((float)(AvgIters - IterNumber) / AvgIters * 0.9);
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uint64_t ExitWeight = PeeledHeaderWeight - FallThruWeight;
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PeeledHeaderWeight -= ExitWeight;
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unsigned HeaderIdx = (LatchBR->getSuccessor(0) == Header ? 0 : 1);
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MDBuilder MDB(LatchBR->getContext());
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MDNode *WeightNode =
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HeaderIdx ? MDB.createBranchWeights(ExitWeight, FallThruWeight)
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: MDB.createBranchWeights(FallThruWeight, ExitWeight);
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LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
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}
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}
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/// \brief Clones the body of the loop L, putting it between \p InsertTop and \p
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/// InsertBot.
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/// \param IterNumber The serial number of the iteration currently being
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/// peeled off.
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/// \param Exit The exit block of the original loop.
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/// \param[out] NewBlocks A list of the blocks in the newly created clone
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/// \param[out] VMap The value map between the loop and the new clone.
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/// \param LoopBlocks A helper for DFS-traversal of the loop.
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/// \param LVMap A value-map that maps instructions from the original loop to
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/// instructions in the last peeled-off iteration.
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static void cloneLoopBlocks(Loop *L, unsigned IterNumber, BasicBlock *InsertTop,
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BasicBlock *InsertBot, BasicBlock *Exit,
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SmallVectorImpl<BasicBlock *> &NewBlocks,
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LoopBlocksDFS &LoopBlocks, ValueToValueMapTy &VMap,
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ValueToValueMapTy &LVMap, DominatorTree *DT,
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LoopInfo *LI) {
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BasicBlock *Header = L->getHeader();
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BasicBlock *Latch = L->getLoopLatch();
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BasicBlock *PreHeader = L->getLoopPreheader();
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Function *F = Header->getParent();
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LoopBlocksDFS::RPOIterator BlockBegin = LoopBlocks.beginRPO();
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LoopBlocksDFS::RPOIterator BlockEnd = LoopBlocks.endRPO();
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Loop *ParentLoop = L->getParentLoop();
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// For each block in the original loop, create a new copy,
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// and update the value map with the newly created values.
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for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
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BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, ".peel", F);
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NewBlocks.push_back(NewBB);
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if (ParentLoop)
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ParentLoop->addBasicBlockToLoop(NewBB, *LI);
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VMap[*BB] = NewBB;
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// If dominator tree is available, insert nodes to represent cloned blocks.
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if (DT) {
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if (Header == *BB)
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DT->addNewBlock(NewBB, InsertTop);
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else {
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DomTreeNode *IDom = DT->getNode(*BB)->getIDom();
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// VMap must contain entry for IDom, as the iteration order is RPO.
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DT->addNewBlock(NewBB, cast<BasicBlock>(VMap[IDom->getBlock()]));
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}
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}
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}
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// Hook-up the control flow for the newly inserted blocks.
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// The new header is hooked up directly to the "top", which is either
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// the original loop preheader (for the first iteration) or the previous
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// iteration's exiting block (for every other iteration)
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InsertTop->getTerminator()->setSuccessor(0, cast<BasicBlock>(VMap[Header]));
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// Similarly, for the latch:
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// The original exiting edge is still hooked up to the loop exit.
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// The backedge now goes to the "bottom", which is either the loop's real
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// header (for the last peeled iteration) or the copied header of the next
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// iteration (for every other iteration)
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BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
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BranchInst *LatchBR = cast<BranchInst>(NewLatch->getTerminator());
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unsigned HeaderIdx = (LatchBR->getSuccessor(0) == Header ? 0 : 1);
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LatchBR->setSuccessor(HeaderIdx, InsertBot);
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LatchBR->setSuccessor(1 - HeaderIdx, Exit);
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if (DT)
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DT->changeImmediateDominator(InsertBot, NewLatch);
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// The new copy of the loop body starts with a bunch of PHI nodes
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// that pick an incoming value from either the preheader, or the previous
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// loop iteration. Since this copy is no longer part of the loop, we
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// resolve this statically:
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// For the first iteration, we use the value from the preheader directly.
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// For any other iteration, we replace the phi with the value generated by
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// the immediately preceding clone of the loop body (which represents
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// the previous iteration).
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for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
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PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
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if (IterNumber == 0) {
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VMap[&*I] = NewPHI->getIncomingValueForBlock(PreHeader);
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} else {
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Value *LatchVal = NewPHI->getIncomingValueForBlock(Latch);
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Instruction *LatchInst = dyn_cast<Instruction>(LatchVal);
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if (LatchInst && L->contains(LatchInst))
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VMap[&*I] = LVMap[LatchInst];
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else
|
|
VMap[&*I] = LatchVal;
|
|
}
|
|
cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI);
|
|
}
|
|
|
|
// Fix up the outgoing values - we need to add a value for the iteration
|
|
// we've just created. Note that this must happen *after* the incoming
|
|
// values are adjusted, since the value going out of the latch may also be
|
|
// a value coming into the header.
|
|
for (BasicBlock::iterator I = Exit->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *PHI = cast<PHINode>(I);
|
|
Value *LatchVal = PHI->getIncomingValueForBlock(Latch);
|
|
Instruction *LatchInst = dyn_cast<Instruction>(LatchVal);
|
|
if (LatchInst && L->contains(LatchInst))
|
|
LatchVal = VMap[LatchVal];
|
|
PHI->addIncoming(LatchVal, cast<BasicBlock>(VMap[Latch]));
|
|
}
|
|
|
|
// LastValueMap is updated with the values for the current loop
|
|
// which are used the next time this function is called.
|
|
for (const auto &KV : VMap)
|
|
LVMap[KV.first] = KV.second;
|
|
}
|
|
|
|
/// \brief Peel off the first \p PeelCount iterations of loop \p L.
|
|
///
|
|
/// Note that this does not peel them off as a single straight-line block.
|
|
/// Rather, each iteration is peeled off separately, and needs to check the
|
|
/// exit condition.
|
|
/// For loops that dynamically execute \p PeelCount iterations or less
|
|
/// this provides a benefit, since the peeled off iterations, which account
|
|
/// for the bulk of dynamic execution, can be further simplified by scalar
|
|
/// optimizations.
|
|
bool llvm::peelLoop(Loop *L, unsigned PeelCount, LoopInfo *LI,
|
|
ScalarEvolution *SE, DominatorTree *DT,
|
|
AssumptionCache *AC, bool PreserveLCSSA) {
|
|
if (!canPeel(L))
|
|
return false;
|
|
|
|
LoopBlocksDFS LoopBlocks(L);
|
|
LoopBlocks.perform(LI);
|
|
|
|
BasicBlock *Header = L->getHeader();
|
|
BasicBlock *PreHeader = L->getLoopPreheader();
|
|
BasicBlock *Latch = L->getLoopLatch();
|
|
BasicBlock *Exit = L->getUniqueExitBlock();
|
|
|
|
Function *F = Header->getParent();
|
|
|
|
// Set up all the necessary basic blocks. It is convenient to split the
|
|
// preheader into 3 parts - two blocks to anchor the peeled copy of the loop
|
|
// body, and a new preheader for the "real" loop.
|
|
|
|
// Peeling the first iteration transforms.
|
|
//
|
|
// PreHeader:
|
|
// ...
|
|
// Header:
|
|
// LoopBody
|
|
// If (cond) goto Header
|
|
// Exit:
|
|
//
|
|
// into
|
|
//
|
|
// InsertTop:
|
|
// LoopBody
|
|
// If (!cond) goto Exit
|
|
// InsertBot:
|
|
// NewPreHeader:
|
|
// ...
|
|
// Header:
|
|
// LoopBody
|
|
// If (cond) goto Header
|
|
// Exit:
|
|
//
|
|
// Each following iteration will split the current bottom anchor in two,
|
|
// and put the new copy of the loop body between these two blocks. That is,
|
|
// after peeling another iteration from the example above, we'll split
|
|
// InsertBot, and get:
|
|
//
|
|
// InsertTop:
|
|
// LoopBody
|
|
// If (!cond) goto Exit
|
|
// InsertBot:
|
|
// LoopBody
|
|
// If (!cond) goto Exit
|
|
// InsertBot.next:
|
|
// NewPreHeader:
|
|
// ...
|
|
// Header:
|
|
// LoopBody
|
|
// If (cond) goto Header
|
|
// Exit:
|
|
|
|
BasicBlock *InsertTop = SplitEdge(PreHeader, Header, DT, LI);
|
|
BasicBlock *InsertBot =
|
|
SplitBlock(InsertTop, InsertTop->getTerminator(), DT, LI);
|
|
BasicBlock *NewPreHeader =
|
|
SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
|
|
|
|
InsertTop->setName(Header->getName() + ".peel.begin");
|
|
InsertBot->setName(Header->getName() + ".peel.next");
|
|
NewPreHeader->setName(PreHeader->getName() + ".peel.newph");
|
|
|
|
ValueToValueMapTy LVMap;
|
|
|
|
// If we have branch weight information, we'll want to update it for the
|
|
// newly created branches.
|
|
BranchInst *LatchBR =
|
|
cast<BranchInst>(cast<BasicBlock>(Latch)->getTerminator());
|
|
unsigned HeaderIdx = (LatchBR->getSuccessor(0) == Header ? 0 : 1);
|
|
|
|
uint64_t TrueWeight, FalseWeight;
|
|
uint64_t ExitWeight = 0, CurHeaderWeight = 0;
|
|
if (LatchBR->extractProfMetadata(TrueWeight, FalseWeight)) {
|
|
ExitWeight = HeaderIdx ? TrueWeight : FalseWeight;
|
|
// The # of times the loop body executes is the sum of the exit block
|
|
// weight and the # of times the backedges are taken.
|
|
CurHeaderWeight = TrueWeight + FalseWeight;
|
|
}
|
|
|
|
// For each peeled-off iteration, make a copy of the loop.
|
|
for (unsigned Iter = 0; Iter < PeelCount; ++Iter) {
|
|
SmallVector<BasicBlock *, 8> NewBlocks;
|
|
ValueToValueMapTy VMap;
|
|
|
|
// Subtract the exit weight from the current header weight -- the exit
|
|
// weight is exactly the weight of the previous iteration's header.
|
|
// FIXME: due to the way the distribution is constructed, we need a
|
|
// guard here to make sure we don't end up with non-positive weights.
|
|
if (ExitWeight < CurHeaderWeight)
|
|
CurHeaderWeight -= ExitWeight;
|
|
else
|
|
CurHeaderWeight = 1;
|
|
|
|
cloneLoopBlocks(L, Iter, InsertTop, InsertBot, Exit,
|
|
NewBlocks, LoopBlocks, VMap, LVMap, DT, LI);
|
|
|
|
// Remap to use values from the current iteration instead of the
|
|
// previous one.
|
|
remapInstructionsInBlocks(NewBlocks, VMap);
|
|
|
|
if (DT) {
|
|
// Latches of the cloned loops dominate over the loop exit, so idom of the
|
|
// latter is the first cloned loop body, as original PreHeader dominates
|
|
// the original loop body.
|
|
if (Iter == 0)
|
|
DT->changeImmediateDominator(Exit, cast<BasicBlock>(LVMap[Latch]));
|
|
assert(DT->verify(DominatorTree::VerificationLevel::Fast));
|
|
}
|
|
|
|
updateBranchWeights(InsertBot, cast<BranchInst>(VMap[LatchBR]), Iter,
|
|
PeelCount, ExitWeight);
|
|
|
|
InsertTop = InsertBot;
|
|
InsertBot = SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
|
|
InsertBot->setName(Header->getName() + ".peel.next");
|
|
|
|
F->getBasicBlockList().splice(InsertTop->getIterator(),
|
|
F->getBasicBlockList(),
|
|
NewBlocks[0]->getIterator(), F->end());
|
|
}
|
|
|
|
// Now adjust the phi nodes in the loop header to get their initial values
|
|
// from the last peeled-off iteration instead of the preheader.
|
|
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *PHI = cast<PHINode>(I);
|
|
Value *NewVal = PHI->getIncomingValueForBlock(Latch);
|
|
Instruction *LatchInst = dyn_cast<Instruction>(NewVal);
|
|
if (LatchInst && L->contains(LatchInst))
|
|
NewVal = LVMap[LatchInst];
|
|
|
|
PHI->setIncomingValue(PHI->getBasicBlockIndex(NewPreHeader), NewVal);
|
|
}
|
|
|
|
// Adjust the branch weights on the loop exit.
|
|
if (ExitWeight) {
|
|
// The backedge count is the difference of current header weight and
|
|
// current loop exit weight. If the current header weight is smaller than
|
|
// the current loop exit weight, we mark the loop backedge weight as 1.
|
|
uint64_t BackEdgeWeight = 0;
|
|
if (ExitWeight < CurHeaderWeight)
|
|
BackEdgeWeight = CurHeaderWeight - ExitWeight;
|
|
else
|
|
BackEdgeWeight = 1;
|
|
MDBuilder MDB(LatchBR->getContext());
|
|
MDNode *WeightNode =
|
|
HeaderIdx ? MDB.createBranchWeights(ExitWeight, BackEdgeWeight)
|
|
: MDB.createBranchWeights(BackEdgeWeight, ExitWeight);
|
|
LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
|
|
}
|
|
|
|
// If the loop is nested, we changed the parent loop, update SE.
|
|
if (Loop *ParentLoop = L->getParentLoop()) {
|
|
SE->forgetLoop(ParentLoop);
|
|
|
|
// FIXME: Incrementally update loop-simplify
|
|
simplifyLoop(ParentLoop, DT, LI, SE, AC, PreserveLCSSA);
|
|
} else {
|
|
// FIXME: Incrementally update loop-simplify
|
|
simplifyLoop(L, DT, LI, SE, AC, PreserveLCSSA);
|
|
}
|
|
|
|
NumPeeled++;
|
|
|
|
return true;
|
|
}
|