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never be true in a well-defined context. The checking for null pointers has been moved into the caller logic so it does not rely on undefined behavior. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210497 91177308-0d34-0410-b5e6-96231b3b80d8
356 lines
13 KiB
C++
356 lines
13 KiB
C++
//===- IVUsers.cpp - Induction Variable Users -------------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements bookkeeping for "interesting" users of expressions
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// computed from induction variables.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/IVUsers.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Type.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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using namespace llvm;
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#define DEBUG_TYPE "iv-users"
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char IVUsers::ID = 0;
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INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
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"Induction Variable Users", false, true)
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INITIALIZE_PASS_DEPENDENCY(LoopInfo)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
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INITIALIZE_PASS_END(IVUsers, "iv-users",
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"Induction Variable Users", false, true)
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Pass *llvm::createIVUsersPass() {
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return new IVUsers();
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}
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/// isInteresting - Test whether the given expression is "interesting" when
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/// used by the given expression, within the context of analyzing the
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/// given loop.
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static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
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ScalarEvolution *SE, LoopInfo *LI) {
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// An addrec is interesting if it's affine or if it has an interesting start.
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if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
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// Keep things simple. Don't touch loop-variant strides unless they're
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// only used outside the loop and we can simplify them.
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if (AR->getLoop() == L)
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return AR->isAffine() ||
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(!L->contains(I) &&
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SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
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// Otherwise recurse to see if the start value is interesting, and that
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// the step value is not interesting, since we don't yet know how to
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// do effective SCEV expansions for addrecs with interesting steps.
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return isInteresting(AR->getStart(), I, L, SE, LI) &&
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!isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
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}
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// An add is interesting if exactly one of its operands is interesting.
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if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
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bool AnyInterestingYet = false;
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for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
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OI != OE; ++OI)
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if (isInteresting(*OI, I, L, SE, LI)) {
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if (AnyInterestingYet)
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return false;
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AnyInterestingYet = true;
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}
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return AnyInterestingYet;
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}
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// Nothing else is interesting here.
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return false;
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}
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/// Return true if all loop headers that dominate this block are in simplified
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/// form.
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static bool isSimplifiedLoopNest(BasicBlock *BB, const DominatorTree *DT,
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const LoopInfo *LI,
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SmallPtrSet<Loop*,16> &SimpleLoopNests) {
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Loop *NearestLoop = nullptr;
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for (DomTreeNode *Rung = DT->getNode(BB);
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Rung; Rung = Rung->getIDom()) {
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BasicBlock *DomBB = Rung->getBlock();
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Loop *DomLoop = LI->getLoopFor(DomBB);
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if (DomLoop && DomLoop->getHeader() == DomBB) {
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// If the domtree walk reaches a loop with no preheader, return false.
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if (!DomLoop->isLoopSimplifyForm())
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return false;
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// If we have already checked this loop nest, stop checking.
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if (SimpleLoopNests.count(DomLoop))
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break;
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// If we have not already checked this loop nest, remember the loop
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// header nearest to BB. The nearest loop may not contain BB.
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if (!NearestLoop)
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NearestLoop = DomLoop;
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}
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}
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if (NearestLoop)
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SimpleLoopNests.insert(NearestLoop);
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return true;
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}
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/// AddUsersImpl - Inspect the specified instruction. If it is a
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/// reducible SCEV, recursively add its users to the IVUsesByStride set and
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/// return true. Otherwise, return false.
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bool IVUsers::AddUsersImpl(Instruction *I,
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SmallPtrSet<Loop*,16> &SimpleLoopNests) {
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// Add this IV user to the Processed set before returning false to ensure that
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// all IV users are members of the set. See IVUsers::isIVUserOrOperand.
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if (!Processed.insert(I))
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return true; // Instruction already handled.
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if (!SE->isSCEVable(I->getType()))
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return false; // Void and FP expressions cannot be reduced.
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// IVUsers is used by LSR which assumes that all SCEV expressions are safe to
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// pass to SCEVExpander. Expressions are not safe to expand if they represent
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// operations that are not safe to speculate, namely integer division.
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if (!isa<PHINode>(I) && !isSafeToSpeculativelyExecute(I, DL))
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return false;
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// LSR is not APInt clean, do not touch integers bigger than 64-bits.
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// Also avoid creating IVs of non-native types. For example, we don't want a
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// 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
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uint64_t Width = SE->getTypeSizeInBits(I->getType());
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if (Width > 64 || (DL && !DL->isLegalInteger(Width)))
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return false;
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// Get the symbolic expression for this instruction.
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const SCEV *ISE = SE->getSCEV(I);
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// If we've come to an uninteresting expression, stop the traversal and
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// call this a user.
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if (!isInteresting(ISE, I, L, SE, LI))
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return false;
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SmallPtrSet<Instruction *, 4> UniqueUsers;
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for (Use &U : I->uses()) {
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Instruction *User = cast<Instruction>(U.getUser());
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if (!UniqueUsers.insert(User))
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continue;
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// Do not infinitely recurse on PHI nodes.
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if (isa<PHINode>(User) && Processed.count(User))
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continue;
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// Only consider IVUsers that are dominated by simplified loop
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// headers. Otherwise, SCEVExpander will crash.
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BasicBlock *UseBB = User->getParent();
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// A phi's use is live out of its predecessor block.
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if (PHINode *PHI = dyn_cast<PHINode>(User)) {
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unsigned OperandNo = U.getOperandNo();
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unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
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UseBB = PHI->getIncomingBlock(ValNo);
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}
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if (!isSimplifiedLoopNest(UseBB, DT, LI, SimpleLoopNests))
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return false;
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// Descend recursively, but not into PHI nodes outside the current loop.
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// It's important to see the entire expression outside the loop to get
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// choices that depend on addressing mode use right, although we won't
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// consider references outside the loop in all cases.
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// If User is already in Processed, we don't want to recurse into it again,
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// but do want to record a second reference in the same instruction.
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bool AddUserToIVUsers = false;
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if (LI->getLoopFor(User->getParent()) != L) {
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if (isa<PHINode>(User) || Processed.count(User) ||
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!AddUsersImpl(User, SimpleLoopNests)) {
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DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
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<< " OF SCEV: " << *ISE << '\n');
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AddUserToIVUsers = true;
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}
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} else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
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DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
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<< " OF SCEV: " << *ISE << '\n');
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AddUserToIVUsers = true;
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}
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if (AddUserToIVUsers) {
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// Okay, we found a user that we cannot reduce.
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IVStrideUse &NewUse = AddUser(User, I);
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// Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
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// The regular return value here is discarded; instead of recording
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// it, we just recompute it when we need it.
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const SCEV *OriginalISE = ISE;
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ISE = TransformForPostIncUse(NormalizeAutodetect,
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ISE, User, I,
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NewUse.PostIncLoops,
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*SE, *DT);
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// PostIncNormalization effectively simplifies the expression under
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// pre-increment assumptions. Those assumptions (no wrapping) might not
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// hold for the post-inc value. Catch such cases by making sure the
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// transformation is invertible.
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if (OriginalISE != ISE) {
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const SCEV *DenormalizedISE =
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TransformForPostIncUse(Denormalize, ISE, User, I,
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NewUse.PostIncLoops, *SE, *DT);
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// If we normalized the expression, but denormalization doesn't give the
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// original one, discard this user.
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if (OriginalISE != DenormalizedISE) {
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DEBUG(dbgs() << " DISCARDING (NORMALIZATION ISN'T INVERTIBLE): "
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<< *ISE << '\n');
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IVUses.pop_back();
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return false;
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}
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}
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DEBUG(if (SE->getSCEV(I) != ISE)
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dbgs() << " NORMALIZED TO: " << *ISE << '\n');
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}
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}
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return true;
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}
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bool IVUsers::AddUsersIfInteresting(Instruction *I) {
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// SCEVExpander can only handle users that are dominated by simplified loop
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// entries. Keep track of all loops that are only dominated by other simple
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// loops so we don't traverse the domtree for each user.
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SmallPtrSet<Loop*,16> SimpleLoopNests;
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return AddUsersImpl(I, SimpleLoopNests);
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}
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IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
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IVUses.push_back(new IVStrideUse(this, User, Operand));
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return IVUses.back();
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}
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IVUsers::IVUsers()
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: LoopPass(ID) {
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initializeIVUsersPass(*PassRegistry::getPassRegistry());
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}
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void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<LoopInfo>();
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addRequired<ScalarEvolution>();
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AU.setPreservesAll();
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}
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bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
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L = l;
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LI = &getAnalysis<LoopInfo>();
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DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
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SE = &getAnalysis<ScalarEvolution>();
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DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
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DL = DLP ? &DLP->getDataLayout() : nullptr;
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// Find all uses of induction variables in this loop, and categorize
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// them by stride. Start by finding all of the PHI nodes in the header for
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// this loop. If they are induction variables, inspect their uses.
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for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
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(void)AddUsersIfInteresting(I);
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return false;
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}
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void IVUsers::print(raw_ostream &OS, const Module *M) const {
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OS << "IV Users for loop ";
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L->getHeader()->printAsOperand(OS, false);
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if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
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OS << " with backedge-taken count "
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<< *SE->getBackedgeTakenCount(L);
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}
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OS << ":\n";
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for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
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E = IVUses.end(); UI != E; ++UI) {
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OS << " ";
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UI->getOperandValToReplace()->printAsOperand(OS, false);
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OS << " = " << *getReplacementExpr(*UI);
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for (PostIncLoopSet::const_iterator
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I = UI->PostIncLoops.begin(),
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E = UI->PostIncLoops.end(); I != E; ++I) {
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OS << " (post-inc with loop ";
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(*I)->getHeader()->printAsOperand(OS, false);
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OS << ")";
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}
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OS << " in ";
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assert(UI->getUser() != nullptr && "Expected non-null User");
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UI->getUser()->print(OS);
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OS << '\n';
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}
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}
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#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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void IVUsers::dump() const {
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print(dbgs());
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}
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#endif
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void IVUsers::releaseMemory() {
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Processed.clear();
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IVUses.clear();
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}
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/// getReplacementExpr - Return a SCEV expression which computes the
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/// value of the OperandValToReplace.
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const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
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return SE->getSCEV(IU.getOperandValToReplace());
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}
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/// getExpr - Return the expression for the use.
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const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
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return
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TransformForPostIncUse(Normalize, getReplacementExpr(IU),
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IU.getUser(), IU.getOperandValToReplace(),
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const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
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*SE, *DT);
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}
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static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
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if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
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if (AR->getLoop() == L)
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return AR;
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return findAddRecForLoop(AR->getStart(), L);
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}
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if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
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for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
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I != E; ++I)
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if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
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return AR;
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return nullptr;
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}
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return nullptr;
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}
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const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
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if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
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return AR->getStepRecurrence(*SE);
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return nullptr;
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}
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void IVStrideUse::transformToPostInc(const Loop *L) {
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PostIncLoops.insert(L);
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}
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void IVStrideUse::deleted() {
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// Remove this user from the list.
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Parent->Processed.erase(this->getUser());
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Parent->IVUses.erase(this);
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// this now dangles!
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}
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