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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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "iv-users"
#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/Target/TargetData.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
using namespace llvm;
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_END(IVUsers, "iv-users",
"Induction Variable Users", false, true)
Pass *llvm::createIVUsersPass() {
return new IVUsers();
}
/// 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 (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
OI != OE; ++OI)
if (isInteresting(*OI, I, L, SE, LI)) {
if (AnyInterestingYet)
return false;
AnyInterestingYet = true;
}
return AnyInterestingYet;
}
// Nothing else is interesting here.
return false;
}
/// AddUsersIfInteresting - 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) {
if (!SE->isSCEVable(I->getType()))
return false; // Void and FP expressions cannot be reduced.
// 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 || (TD && !TD->isLegalInteger(Width)))
return false;
if (!Processed.insert(I))
return true; // Instruction already handled.
// 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 (Value::use_iterator UI = I->use_begin(), E = I->use_end();
UI != E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
if (!UniqueUsers.insert(User))
continue;
// Do not infinitely recurse on PHI nodes.
if (isa<PHINode>(User) && Processed.count(User))
continue;
// 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) ||
!AddUsersIfInteresting(User)) {
DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
<< " OF SCEV: " << *ISE << '\n');
AddUserToIVUsers = true;
}
} else if (Processed.count(User) || !AddUsersIfInteresting(User)) {
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();
// 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.
ISE = TransformForPostIncUse(NormalizeAutodetect,
ISE, User, I,
NewUse.PostIncLoops,
*SE, *DT);
DEBUG(dbgs() << " NORMALIZED TO: " << *ISE << '\n');
}
}
return true;
}
IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
IVUses.push_back(new IVStrideUse(this, User, Operand));
return IVUses.back();
}
IVUsers::IVUsers()
: LoopPass(ID) {
initializeIVUsersPass(*PassRegistry::getPassRegistry());
}
void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LoopInfo>();
AU.addRequired<DominatorTree>();
AU.addRequired<ScalarEvolution>();
AU.setPreservesAll();
}
bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
L = l;
LI = &getAnalysis<LoopInfo>();
DT = &getAnalysis<DominatorTree>();
SE = &getAnalysis<ScalarEvolution>();
TD = getAnalysisIfAvailable<TargetData>();
// 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);
return false;
}
void IVUsers::print(raw_ostream &OS, const Module *M) const {
OS << "IV Users for loop ";
WriteAsOperand(OS, L->getHeader(), false);
if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
OS << " with backedge-taken count "
<< *SE->getBackedgeTakenCount(L);
}
OS << ":\n";
for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
E = IVUses.end(); UI != E; ++UI) {
OS << " ";
WriteAsOperand(OS, UI->getOperandValToReplace(), 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);
OS << ")";
}
OS << " in ";
UI->getUser()->print(OS);
OS << '\n';
}
}
void IVUsers::dump() const {
print(dbgs());
}
void IVUsers::releaseMemory() {
Processed.clear();
IVUses.clear();
}
/// 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
TransformForPostIncUse(Normalize, getReplacementExpr(IU),
IU.getUser(), IU.getOperandValToReplace(),
const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
*SE, *DT);
}
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 (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
I != E; ++I)
if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
return AR;
return 0;
}
return 0;
}
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;
}
void IVStrideUse::transformToPostInc(const Loop *L) {
PostIncLoops.insert(L);
}
void IVStrideUse::deleted() {
// Remove this user from the list.
Parent->IVUses.erase(this);
// this now dangles!
}
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