llvm/lib/Analysis/IVUsers.cpp
Dan Gohman eaa40ff74e Make IVUsers iterative instead of recursive.
This has the side effect of reversing the order of most of
IVUser's results.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112442 91177308-0d34-0410-b5e6-96231b3b80d8
2010-08-29 16:40:03 +00:00

271 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();
}
/// findInterestingAddRec - Test whether the given expression is interesting.
/// Return the addrec with the current loop which makes it interesting, or
/// null if it is not interesting.
const SCEVAddRecExpr *IVUsers::findInterestingAddRec(const SCEV *S) const {
// 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;
// We don't yet know how to do effective SCEV expansions for addrecs
// with interesting steps.
if (findInterestingAddRec(AR->getStepRecurrence(*SE)))
return 0;
// Otherwise recurse to see if the start value is interesting.
return findInterestingAddRec(AR->getStart());
}
// An add is interesting if exactly one of its operands is interesting.
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
OI != OE; ++OI)
if (const SCEVAddRecExpr *AR = findInterestingAddRec(*OI))
return AR;
return 0;
}
// Nothing else is interesting here.
return 0;
}
bool IVUsers::isInterestingUser(const Instruction *User) const {
// Void and FP expressions cannot be reduced.
if (!SE->isSCEVable(User->getType()))
return false;
// LSR is not APInt clean, do not touch integers bigger than 64-bits.
if (SE->getTypeSizeInBits(User->getType()) > 64)
return false;
// Don't descend into PHI nodes outside the current loop.
if (LI->getLoopFor(User->getParent()) != L &&
isa<PHINode>(User))
return false;
// Otherwise, it may be interesting.
return true;
}
/// 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.
void IVUsers::AddUsersIfInteresting(Instruction *I) {
// Stop if we've seen this before.
if (!Processed.insert(I))
return;
// If this PHI node is not SCEVable, ignore it.
if (!SE->isSCEVable(I->getType()))
return;
// If this PHI node is not an addrec for this loop, ignore it.
const SCEVAddRecExpr *Expr = findInterestingAddRec(SE->getSCEV(I));
if (!Expr)
return;
// Walk the def-use graph.
SmallVector<std::pair<Instruction *, const SCEVAddRecExpr *>, 16> Worklist;
Worklist.push_back(std::make_pair(I, Expr));
do {
std::pair<Instruction *, const SCEVAddRecExpr *> P =
Worklist.pop_back_val();
Instruction *Op = P.first;
const SCEVAddRecExpr *OpAR = P.second;
// Visit Op's users.
SmallPtrSet<Instruction *, 8> VisitedUsers;
for (Value::use_iterator UI = Op->use_begin(), E = Op->use_end();
UI != E; ++UI) {
// Don't visit any individual user more than once.
Instruction *User = cast<Instruction>(*UI);
if (!VisitedUsers.insert(User))
continue;
// If it's an affine addrec (which we can pretty safely re-expand) inside
// the loop, or a potentially non-affine addrec outside the loop (which
// we can evaluate outside of the loop), follow it.
if (OpAR->isAffine() || !L->contains(User)) {
if (isInterestingUser(User)) {
const SCEV *UserExpr = SE->getSCEV(User);
if (const SCEVAddRecExpr *AR = findInterestingAddRec(UserExpr)) {
// Interesting. Keep searching.
if (Processed.insert(User))
Worklist.push_back(std::make_pair(User, AR));
continue;
}
}
}
// Otherwise, this is the point where the def-use chain
// becomes uninteresting. Call it an IV User.
AddUser(User, Op);
}
} while (!Worklist.empty());
}
IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
IVUses.push_back(new IVStrideUse(this, User, Operand));
IVStrideUse &NewUse = IVUses.back();
// Auto-detect and remember post-inc loops for this expression.
const SCEV *S = SE->getSCEV(Operand);
(void)TransformForPostIncUse(NormalizeAutodetect,
S, User, Operand,
NewUse.PostIncLoops,
*SE, *DT);
return NewUse;
}
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)
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!
}