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Imported Upstream version 5.18.0.207

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Former-commit-id: 3b152f462918d427ce18620a2cbe4f8b79650449
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Xamarin Public Jenkins (auto-signing)
2018-11-17 08:23:10 +00:00
parent 8e12397d70
commit eb85e2fc17
28480 changed files with 72 additions and 3866936 deletions
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external/llvm/lib/Analysis/IVUsers.cpp vendored
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//===- IVUsers.cpp - Induction Variable Users -------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements bookkeeping for "interesting" users of expressions
// computed from induction variables.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/IVUsers.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/LoopAnalysisManager.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
using namespace llvm;
#define DEBUG_TYPE "iv-users"
AnalysisKey IVUsersAnalysis::Key;
IVUsers IVUsersAnalysis::run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR) {
return IVUsers(&L, &AR.AC, &AR.LI, &AR.DT, &AR.SE);
}
char IVUsersWrapperPass::ID = 0;
INITIALIZE_PASS_BEGIN(IVUsersWrapperPass, "iv-users",
"Induction Variable Users", false, true)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_END(IVUsersWrapperPass, "iv-users", "Induction Variable Users",
false, true)
Pass *llvm::createIVUsersPass() { return new IVUsersWrapperPass(); }
/// isInteresting - Test whether the given expression is "interesting" when
/// used by the given expression, within the context of analyzing the
/// given loop.
static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
ScalarEvolution *SE, LoopInfo *LI) {
// An addrec is interesting if it's affine or if it has an interesting start.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
// Keep things simple. Don't touch loop-variant strides unless they're
// only used outside the loop and we can simplify them.
if (AR->getLoop() == L)
return AR->isAffine() ||
(!L->contains(I) &&
SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
// Otherwise recurse to see if the start value is interesting, and that
// the step value is not interesting, since we don't yet know how to
// do effective SCEV expansions for addrecs with interesting steps.
return isInteresting(AR->getStart(), I, L, SE, LI) &&
!isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
}
// An add is interesting if exactly one of its operands is interesting.
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
bool AnyInterestingYet = false;
for (const auto *Op : Add->operands())
if (isInteresting(Op, I, L, SE, LI)) {
if (AnyInterestingYet)
return false;
AnyInterestingYet = true;
}
return AnyInterestingYet;
}
// Nothing else is interesting here.
return false;
}
/// Return true if all loop headers that dominate this block are in simplified
/// form.
static bool isSimplifiedLoopNest(BasicBlock *BB, const DominatorTree *DT,
const LoopInfo *LI,
SmallPtrSetImpl<Loop*> &SimpleLoopNests) {
Loop *NearestLoop = nullptr;
for (DomTreeNode *Rung = DT->getNode(BB);
Rung; Rung = Rung->getIDom()) {
BasicBlock *DomBB = Rung->getBlock();
Loop *DomLoop = LI->getLoopFor(DomBB);
if (DomLoop && DomLoop->getHeader() == DomBB) {
// If the domtree walk reaches a loop with no preheader, return false.
if (!DomLoop->isLoopSimplifyForm())
return false;
// If we have already checked this loop nest, stop checking.
if (SimpleLoopNests.count(DomLoop))
break;
// If we have not already checked this loop nest, remember the loop
// header nearest to BB. The nearest loop may not contain BB.
if (!NearestLoop)
NearestLoop = DomLoop;
}
}
if (NearestLoop)
SimpleLoopNests.insert(NearestLoop);
return true;
}
/// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
/// and now we need to decide whether the user should use the preinc or post-inc
/// value. If this user should use the post-inc version of the IV, return true.
///
/// Choosing wrong here can break dominance properties (if we choose to use the
/// post-inc value when we cannot) or it can end up adding extra live-ranges to
/// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
/// should use the post-inc value).
static bool IVUseShouldUsePostIncValue(Instruction *User, Value *Operand,
const Loop *L, DominatorTree *DT) {
// If the user is in the loop, use the preinc value.
if (L->contains(User))
return false;
BasicBlock *LatchBlock = L->getLoopLatch();
if (!LatchBlock)
return false;
// Ok, the user is outside of the loop. If it is dominated by the latch
// block, use the post-inc value.
if (DT->dominates(LatchBlock, User->getParent()))
return true;
// There is one case we have to be careful of: PHI nodes. These little guys
// can live in blocks that are not dominated by the latch block, but (since
// their uses occur in the predecessor block, not the block the PHI lives in)
// should still use the post-inc value. Check for this case now.
PHINode *PN = dyn_cast<PHINode>(User);
if (!PN || !Operand)
return false; // not a phi, not dominated by latch block.
// Look at all of the uses of Operand by the PHI node. If any use corresponds
// to a block that is not dominated by the latch block, give up and use the
// preincremented value.
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == Operand &&
!DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
return false;
// Okay, all uses of Operand by PN are in predecessor blocks that really are
// dominated by the latch block. Use the post-incremented value.
return true;
}
/// AddUsersImpl - Inspect the specified instruction. If it is a
/// reducible SCEV, recursively add its users to the IVUsesByStride set and
/// return true. Otherwise, return false.
bool IVUsers::AddUsersImpl(Instruction *I,
SmallPtrSetImpl<Loop*> &SimpleLoopNests) {
const DataLayout &DL = I->getModule()->getDataLayout();
// Add this IV user to the Processed set before returning false to ensure that
// all IV users are members of the set. See IVUsers::isIVUserOrOperand.
if (!Processed.insert(I).second)
return true; // Instruction already handled.
if (!SE->isSCEVable(I->getType()))
return false; // Void and FP expressions cannot be reduced.
// IVUsers is used by LSR which assumes that all SCEV expressions are safe to
// pass to SCEVExpander. Expressions are not safe to expand if they represent
// operations that are not safe to speculate, namely integer division.
if (!isa<PHINode>(I) && !isSafeToSpeculativelyExecute(I))
return false;
// LSR is not APInt clean, do not touch integers bigger than 64-bits.
// Also avoid creating IVs of non-native types. For example, we don't want a
// 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
uint64_t Width = SE->getTypeSizeInBits(I->getType());
if (Width > 64 || !DL.isLegalInteger(Width))
return false;
// Don't attempt to promote ephemeral values to indvars. They will be removed
// later anyway.
if (EphValues.count(I))
return false;
// Get the symbolic expression for this instruction.
const SCEV *ISE = SE->getSCEV(I);
// If we've come to an uninteresting expression, stop the traversal and
// call this a user.
if (!isInteresting(ISE, I, L, SE, LI))
return false;
SmallPtrSet<Instruction *, 4> UniqueUsers;
for (Use &U : I->uses()) {
Instruction *User = cast<Instruction>(U.getUser());
if (!UniqueUsers.insert(User).second)
continue;
// Do not infinitely recurse on PHI nodes.
if (isa<PHINode>(User) && Processed.count(User))
continue;
// Only consider IVUsers that are dominated by simplified loop
// headers. Otherwise, SCEVExpander will crash.
BasicBlock *UseBB = User->getParent();
// A phi's use is live out of its predecessor block.
if (PHINode *PHI = dyn_cast<PHINode>(User)) {
unsigned OperandNo = U.getOperandNo();
unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
UseBB = PHI->getIncomingBlock(ValNo);
}
if (!isSimplifiedLoopNest(UseBB, DT, LI, SimpleLoopNests))
return false;
// Descend recursively, but not into PHI nodes outside the current loop.
// It's important to see the entire expression outside the loop to get
// choices that depend on addressing mode use right, although we won't
// consider references outside the loop in all cases.
// If User is already in Processed, we don't want to recurse into it again,
// but do want to record a second reference in the same instruction.
bool AddUserToIVUsers = false;
if (LI->getLoopFor(User->getParent()) != L) {
if (isa<PHINode>(User) || Processed.count(User) ||
!AddUsersImpl(User, SimpleLoopNests)) {
DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
<< " OF SCEV: " << *ISE << '\n');
AddUserToIVUsers = true;
}
} else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
<< " OF SCEV: " << *ISE << '\n');
AddUserToIVUsers = true;
}
if (AddUserToIVUsers) {
// Okay, we found a user that we cannot reduce.
IVStrideUse &NewUse = AddUser(User, I);
// Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
// The regular return value here is discarded; instead of recording
// it, we just recompute it when we need it.
const SCEV *OriginalISE = ISE;
auto NormalizePred = [&](const SCEVAddRecExpr *AR) {
auto *L = AR->getLoop();
bool Result = IVUseShouldUsePostIncValue(User, I, L, DT);
if (Result)
NewUse.PostIncLoops.insert(L);
return Result;
};
ISE = normalizeForPostIncUseIf(ISE, NormalizePred, *SE);
// PostIncNormalization effectively simplifies the expression under
// pre-increment assumptions. Those assumptions (no wrapping) might not
// hold for the post-inc value. Catch such cases by making sure the
// transformation is invertible.
if (OriginalISE != ISE) {
const SCEV *DenormalizedISE =
denormalizeForPostIncUse(ISE, NewUse.PostIncLoops, *SE);
// If we normalized the expression, but denormalization doesn't give the
// original one, discard this user.
if (OriginalISE != DenormalizedISE) {
DEBUG(dbgs() << " DISCARDING (NORMALIZATION ISN'T INVERTIBLE): "
<< *ISE << '\n');
IVUses.pop_back();
return false;
}
}
DEBUG(if (SE->getSCEV(I) != ISE)
dbgs() << " NORMALIZED TO: " << *ISE << '\n');
}
}
return true;
}
bool IVUsers::AddUsersIfInteresting(Instruction *I) {
// SCEVExpander can only handle users that are dominated by simplified loop
// entries. Keep track of all loops that are only dominated by other simple
// loops so we don't traverse the domtree for each user.
SmallPtrSet<Loop*,16> SimpleLoopNests;
return AddUsersImpl(I, SimpleLoopNests);
}
IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
IVUses.push_back(new IVStrideUse(this, User, Operand));
return IVUses.back();
}
IVUsers::IVUsers(Loop *L, AssumptionCache *AC, LoopInfo *LI, DominatorTree *DT,
ScalarEvolution *SE)
: L(L), AC(AC), LI(LI), DT(DT), SE(SE), IVUses() {
// Collect ephemeral values so that AddUsersIfInteresting skips them.
EphValues.clear();
CodeMetrics::collectEphemeralValues(L, AC, EphValues);
// Find all uses of induction variables in this loop, and categorize
// them by stride. Start by finding all of the PHI nodes in the header for
// this loop. If they are induction variables, inspect their uses.
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
(void)AddUsersIfInteresting(&*I);
}
void IVUsers::print(raw_ostream &OS, const Module *M) const {
OS << "IV Users for loop ";
L->getHeader()->printAsOperand(OS, false);
if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
OS << " with backedge-taken count " << *SE->getBackedgeTakenCount(L);
}
OS << ":\n";
for (const IVStrideUse &IVUse : IVUses) {
OS << " ";
IVUse.getOperandValToReplace()->printAsOperand(OS, false);
OS << " = " << *getReplacementExpr(IVUse);
for (auto PostIncLoop : IVUse.PostIncLoops) {
OS << " (post-inc with loop ";
PostIncLoop->getHeader()->printAsOperand(OS, false);
OS << ")";
}
OS << " in ";
if (IVUse.getUser())
IVUse.getUser()->print(OS);
else
OS << "Printing <null> User";
OS << '\n';
}
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void IVUsers::dump() const { print(dbgs()); }
#endif
void IVUsers::releaseMemory() {
Processed.clear();
IVUses.clear();
}
IVUsersWrapperPass::IVUsersWrapperPass() : LoopPass(ID) {
initializeIVUsersWrapperPassPass(*PassRegistry::getPassRegistry());
}
void IVUsersWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<LoopInfoWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<ScalarEvolutionWrapperPass>();
AU.setPreservesAll();
}
bool IVUsersWrapperPass::runOnLoop(Loop *L, LPPassManager &LPM) {
auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
*L->getHeader()->getParent());
auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
IU.reset(new IVUsers(L, AC, LI, DT, SE));
return false;
}
void IVUsersWrapperPass::print(raw_ostream &OS, const Module *M) const {
IU->print(OS, M);
}
void IVUsersWrapperPass::releaseMemory() { IU->releaseMemory(); }
/// getReplacementExpr - Return a SCEV expression which computes the
/// value of the OperandValToReplace.
const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
return SE->getSCEV(IU.getOperandValToReplace());
}
/// getExpr - Return the expression for the use.
const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
return normalizeForPostIncUse(getReplacementExpr(IU), IU.getPostIncLoops(),
*SE);
}
static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
if (AR->getLoop() == L)
return AR;
return findAddRecForLoop(AR->getStart(), L);
}
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
for (const auto *Op : Add->operands())
if (const SCEVAddRecExpr *AR = findAddRecForLoop(Op, L))
return AR;
return nullptr;
}
return nullptr;
}
const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
return AR->getStepRecurrence(*SE);
return nullptr;
}
void IVStrideUse::transformToPostInc(const Loop *L) {
PostIncLoops.insert(L);
}
void IVStrideUse::deleted() {
// Remove this user from the list.
Parent->Processed.erase(this->getUser());
Parent->IVUses.erase(this);
// this now dangles!
}