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llvm-mirror/lib/Analysis/IVUsers.cpp
Reid Kleckner 68092989f3 Sink all InitializePasses.h includes
This file lists every pass in LLVM, and is included by Pass.h, which is
very popular. Every time we add, remove, or rename a pass in LLVM, it
caused lots of recompilation.

I found this fact by looking at this table, which is sorted by the
number of times a file was changed over the last 100,000 git commits
multiplied by the number of object files that depend on it in the
current checkout:
  recompiles    touches affected_files  header
  342380        95      3604    llvm/include/llvm/ADT/STLExtras.h
  314730        234     1345    llvm/include/llvm/InitializePasses.h
  307036        118     2602    llvm/include/llvm/ADT/APInt.h
  213049        59      3611    llvm/include/llvm/Support/MathExtras.h
  170422        47      3626    llvm/include/llvm/Support/Compiler.h
  162225        45      3605    llvm/include/llvm/ADT/Optional.h
  158319        63      2513    llvm/include/llvm/ADT/Triple.h
  140322        39      3598    llvm/include/llvm/ADT/StringRef.h
  137647        59      2333    llvm/include/llvm/Support/Error.h
  131619        73      1803    llvm/include/llvm/Support/FileSystem.h

Before this change, touching InitializePasses.h would cause 1345 files
to recompile. After this change, touching it only causes 550 compiles in
an incremental rebuild.

Reviewers: bkramer, asbirlea, bollu, jdoerfert

Differential Revision: https://reviews.llvm.org/D70211
2019-11-13 16:34:37 -08:00

428 lines
16 KiB
C++

//===- IVUsers.cpp - Induction Variable Users -------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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/Config/llvm-config.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/InitializePasses.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)) {
LLVM_DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
<< " OF SCEV: " << *ISE << '\n');
AddUserToIVUsers = true;
}
} else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
LLVM_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) {
LLVM_DEBUG(dbgs()
<< " DISCARDING (NORMALIZATION ISN'T INVERTIBLE): "
<< *ISE << '\n');
IVUses.pop_back();
return false;
}
}
LLVM_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!
}