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llvm-mirror/lib/Analysis/IVUsers.cpp
Dan Gohman ee89338e37 Tweak IVUsers' concept of "interesting" to exclude add recurrences
where the step value is an induction variable from an outer loop, to
avoid trouble trying to re-expand such expressions. This effectively
hides such expressions from indvars and lsr, which prevents them
from getting into trouble.

llvm-svn: 111317
2010-08-17 22:50:37 +00:00

260 lines
8.7 KiB
C++

//===- 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/Assembly/AsmAnnotationWriter.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(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) {
// 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.
if (AR->getLoop() == L)
return AR->isAffine() || !L->contains(I);
// 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);
}
// 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)) {
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.
if (SE->getTypeSizeInBits(I->getType()) > 64)
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))
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();
// Transform the expression into a normalized form.
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) {
}
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>();
// 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";
// Use a default AssemblyAnnotationWriter to suppress the default info
// comments, which aren't relevant here.
AssemblyAnnotationWriter Annotator;
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, &Annotator);
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!
}