//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "iv-users"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/IVUsers.h"
-#include "llvm/Constants.h"
-#include "llvm/Instructions.h"
-#include "llvm/Type.h"
-#include "llvm/DerivedTypes.h"
-#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
-#include "llvm/ADT/STLExtras.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"
+
char IVUsers::ID = 0;
INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
"Induction Variable Users", false, true)
-INITIALIZE_PASS_DEPENDENCY(LoopInfo)
-INITIALIZE_PASS_DEPENDENCY(DominatorTree)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_END(IVUsers, "iv-users",
"Induction Variable Users", false, true)
/// 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) {
+ 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.
+ // 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);
+ 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) &&
- !isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
+ 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.
bool AnyInterestingYet = false;
for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
OI != OE; ++OI)
- if (isInteresting(*OI, I, L, SE)) {
+ if (isInteresting(*OI, I, L, SE, LI)) {
if (AnyInterestingYet)
return false;
AnyInterestingYet = true;
return false;
}
-/// AddUsersIfInteresting - Inspect the specified instruction. If it is a
+/// 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;
+}
+
+/// 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::AddUsersIfInteresting(Instruction *I) {
+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.
- if (SE->getTypeSizeInBits(I->getType()) > 64)
+ // 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;
- if (!Processed.insert(I))
- return true; // Instruction already handled.
+ // 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))
+ if (!isInteresting(ISE, I, L, SE, LI))
return false;
SmallPtrSet<Instruction *, 4> UniqueUsers;
- for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
- UI != E; ++UI) {
- Instruction *User = cast<Instruction>(*UI);
- if (!UniqueUsers.insert(User))
+ 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
bool AddUserToIVUsers = false;
if (LI->getLoopFor(User->getParent()) != L) {
if (isa<PHINode>(User) || Processed.count(User) ||
- !AddUsersIfInteresting(User)) {
+ !AddUsersImpl(User, SimpleLoopNests)) {
DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
<< " OF SCEV: " << *ISE << '\n');
AddUserToIVUsers = true;
}
- } else if (Processed.count(User) ||
- !AddUsersIfInteresting(User)) {
+ } 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.
- IVUses.push_back(new IVStrideUse(this, User, I));
- IVStrideUse &NewUse = IVUses.back();
- // Transform the expression into a normalized form.
+ 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;
ISE = TransformForPostIncUse(NormalizeAutodetect,
ISE, User, I,
NewUse.PostIncLoops,
*SE, *DT);
- DEBUG(dbgs() << " NORMALIZED TO: " << *ISE << '\n');
+
+ // 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 =
+ TransformForPostIncUse(Denormalize, ISE, User, I,
+ NewUse.PostIncLoops, *SE, *DT);
+
+ // 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();
}
void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<LoopInfo>();
- AU.addRequired<DominatorTree>();
- AU.addRequired<ScalarEvolution>();
+ AU.addRequired<AssumptionCacheTracker>();
+ AU.addRequired<LoopInfoWrapperPass>();
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addRequired<ScalarEvolutionWrapperPass>();
AU.setPreservesAll();
}
bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
L = l;
- LI = &getAnalysis<LoopInfo>();
- DT = &getAnalysis<DominatorTree>();
- SE = &getAnalysis<ScalarEvolution>();
+ AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
+ *L->getHeader()->getParent());
+ LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+ DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
+
+ // 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)AddUsersIfInteresting(&*I);
return false;
}
void IVUsers::print(raw_ostream &OS, const Module *M) const {
OS << "IV Users for loop ";
- WriteAsOperand(OS, L->getHeader(), false);
+ L->getHeader()->printAsOperand(OS, false);
if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
OS << " with backedge-taken count "
<< *SE->getBackedgeTakenCount(L);
for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
E = IVUses.end(); UI != E; ++UI) {
OS << " ";
- WriteAsOperand(OS, UI->getOperandValToReplace(), false);
+ UI->getOperandValToReplace()->printAsOperand(OS, false);
OS << " = " << *getReplacementExpr(*UI);
for (PostIncLoopSet::const_iterator
I = UI->PostIncLoops.begin(),
E = UI->PostIncLoops.end(); I != E; ++I) {
OS << " (post-inc with loop ";
- WriteAsOperand(OS, (*I)->getHeader(), false);
+ (*I)->getHeader()->printAsOperand(OS, false);
OS << ")";
}
OS << " in ";
- UI->getUser()->print(OS);
+ if (UI->getUser())
+ UI->getUser()->print(OS);
+ else
+ OS << "Printing <null> User";
OS << '\n';
}
}
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void IVUsers::dump() const {
print(dbgs());
}
+#endif
void IVUsers::releaseMemory() {
Processed.clear();
I != E; ++I)
if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
return AR;
- return 0;
+ return nullptr;
}
- return 0;
+ 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 0;
+ return nullptr;
}
void IVStrideUse::transformToPostInc(const Loop *L) {
void IVStrideUse::deleted() {
// Remove this user from the list.
+ Parent->Processed.erase(this->getUser());
Parent->IVUses.erase(this);
// this now dangles!
}
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