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llvm-6502/lib/Transforms/Scalar/IndVarSimplify.cpp
Dan Gohman d594e6f034 Change ScalarEvolution::getSCEVAtScope to always return the original value 
in the case where a loop exit value cannot be computed, instead of only in
some cases while using SCEVCouldNotCompute in others. This simplifies
getSCEVAtScope's callers.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72375 91177308-0d34-0410-b5e6-96231b3b80d8
2009-05-24 23:25:42 +00:00

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//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This transformation analyzes and transforms the induction variables (and
// computations derived from them) into simpler forms suitable for subsequent
// analysis and transformation.
//
// This transformation makes the following changes to each loop with an
// identifiable induction variable:
// 1. All loops are transformed to have a SINGLE canonical induction variable
// which starts at zero and steps by one.
// 2. The canonical induction variable is guaranteed to be the first PHI node
// in the loop header block.
// 3. Any pointer arithmetic recurrences are raised to use array subscripts.
//
// If the trip count of a loop is computable, this pass also makes the following
// changes:
// 1. The exit condition for the loop is canonicalized to compare the
// induction value against the exit value. This turns loops like:
// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
// 2. Any use outside of the loop of an expression derived from the indvar
// is changed to compute the derived value outside of the loop, eliminating
// the dependence on the exit value of the induction variable. If the only
// purpose of the loop is to compute the exit value of some derived
// expression, this transformation will make the loop dead.
//
// This transformation should be followed by strength reduction after all of the
// desired loop transformations have been performed.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "indvars"
#include "llvm/Transforms/Scalar.h"
#include "llvm/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/IVUsers.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
STATISTIC(NumRemoved , "Number of aux indvars removed");
STATISTIC(NumInserted, "Number of canonical indvars added");
STATISTIC(NumReplaced, "Number of exit values replaced");
STATISTIC(NumLFTR , "Number of loop exit tests replaced");
namespace {
class VISIBILITY_HIDDEN IndVarSimplify : public LoopPass {
IVUsers *IU;
LoopInfo *LI;
ScalarEvolution *SE;
bool Changed;
public:
static char ID; // Pass identification, replacement for typeid
IndVarSimplify() : LoopPass(&ID) {}
virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominatorTree>();
AU.addRequired<ScalarEvolution>();
AU.addRequiredID(LCSSAID);
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<LoopInfo>();
AU.addRequired<IVUsers>();
AU.addPreserved<ScalarEvolution>();
AU.addPreservedID(LoopSimplifyID);
AU.addPreserved<IVUsers>();
AU.addPreservedID(LCSSAID);
AU.setPreservesCFG();
}
private:
void RewriteNonIntegerIVs(Loop *L);
ICmpInst *LinearFunctionTestReplace(Loop *L, SCEVHandle BackedgeTakenCount,
Value *IndVar,
BasicBlock *ExitingBlock,
BranchInst *BI,
SCEVExpander &Rewriter);
void RewriteLoopExitValues(Loop *L, const SCEV *BackedgeTakenCount);
void RewriteIVExpressions(Loop *L, const Type *LargestType,
SCEVExpander &Rewriter);
void SinkUnusedInvariants(Loop *L, SCEVExpander &Rewriter);
void FixUsesBeforeDefs(Loop *L, SCEVExpander &Rewriter);
void HandleFloatingPointIV(Loop *L, PHINode *PH);
};
}
char IndVarSimplify::ID = 0;
static RegisterPass<IndVarSimplify>
X("indvars", "Canonicalize Induction Variables");
Pass *llvm::createIndVarSimplifyPass() {
return new IndVarSimplify();
}
/// LinearFunctionTestReplace - This method rewrites the exit condition of the
/// loop to be a canonical != comparison against the incremented loop induction
/// variable. This pass is able to rewrite the exit tests of any loop where the
/// SCEV analysis can determine a loop-invariant trip count of the loop, which
/// is actually a much broader range than just linear tests.
ICmpInst *IndVarSimplify::LinearFunctionTestReplace(Loop *L,
SCEVHandle BackedgeTakenCount,
Value *IndVar,
BasicBlock *ExitingBlock,
BranchInst *BI,
SCEVExpander &Rewriter) {
// If the exiting block is not the same as the backedge block, we must compare
// against the preincremented value, otherwise we prefer to compare against
// the post-incremented value.
Value *CmpIndVar;
SCEVHandle RHS = BackedgeTakenCount;
if (ExitingBlock == L->getLoopLatch()) {
// Add one to the "backedge-taken" count to get the trip count.
// If this addition may overflow, we have to be more pessimistic and
// cast the induction variable before doing the add.
SCEVHandle Zero = SE->getIntegerSCEV(0, BackedgeTakenCount->getType());
SCEVHandle N =
SE->getAddExpr(BackedgeTakenCount,
SE->getIntegerSCEV(1, BackedgeTakenCount->getType()));
if ((isa<SCEVConstant>(N) && !N->isZero()) ||
SE->isLoopGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
// No overflow. Cast the sum.
RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType());
} else {
// Potential overflow. Cast before doing the add.
RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
IndVar->getType());
RHS = SE->getAddExpr(RHS,
SE->getIntegerSCEV(1, IndVar->getType()));
}
// The BackedgeTaken expression contains the number of times that the
// backedge branches to the loop header. This is one less than the
// number of times the loop executes, so use the incremented indvar.
CmpIndVar = L->getCanonicalInductionVariableIncrement();
} else {
// We have to use the preincremented value...
RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
IndVar->getType());
CmpIndVar = IndVar;
}
// Expand the code for the iteration count into the preheader of the loop.
BasicBlock *Preheader = L->getLoopPreheader();
Value *ExitCnt = Rewriter.expandCodeFor(RHS, CmpIndVar->getType(),
Preheader->getTerminator());
// Insert a new icmp_ne or icmp_eq instruction before the branch.
ICmpInst::Predicate Opcode;
if (L->contains(BI->getSuccessor(0)))
Opcode = ICmpInst::ICMP_NE;
else
Opcode = ICmpInst::ICMP_EQ;
DOUT << "INDVARS: Rewriting loop exit condition to:\n"
<< " LHS:" << *CmpIndVar // includes a newline
<< " op:\t"
<< (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
<< " RHS:\t" << *RHS << "\n";
ICmpInst *Cond = new ICmpInst(Opcode, CmpIndVar, ExitCnt, "exitcond", BI);
Instruction *OrigCond = cast<Instruction>(BI->getCondition());
// It's tempting to use replaceAllUsesWith here to fully replace the old
// comparison, but that's not immediately safe, since users of the old
// comparison may not be dominated by the new comparison. Instead, just
// update the branch to use the new comparison; in the common case this
// will make old comparison dead.
BI->setCondition(Cond);
RecursivelyDeleteTriviallyDeadInstructions(OrigCond);
++NumLFTR;
Changed = true;
return Cond;
}
/// RewriteLoopExitValues - Check to see if this loop has a computable
/// loop-invariant execution count. If so, this means that we can compute the
/// final value of any expressions that are recurrent in the loop, and
/// substitute the exit values from the loop into any instructions outside of
/// the loop that use the final values of the current expressions.
///
/// This is mostly redundant with the regular IndVarSimplify activities that
/// happen later, except that it's more powerful in some cases, because it's
/// able to brute-force evaluate arbitrary instructions as long as they have
/// constant operands at the beginning of the loop.
void IndVarSimplify::RewriteLoopExitValues(Loop *L,
const SCEV *BackedgeTakenCount) {
// Verify the input to the pass in already in LCSSA form.
assert(L->isLCSSAForm());
BasicBlock *Preheader = L->getLoopPreheader();
// Scan all of the instructions in the loop, looking at those that have
// extra-loop users and which are recurrences.
SCEVExpander Rewriter(*SE);
// We insert the code into the preheader of the loop if the loop contains
// multiple exit blocks, or in the exit block if there is exactly one.
BasicBlock *BlockToInsertInto;
SmallVector<BasicBlock*, 8> ExitBlocks;
L->getUniqueExitBlocks(ExitBlocks);
if (ExitBlocks.size() == 1)
BlockToInsertInto = ExitBlocks[0];
else
BlockToInsertInto = Preheader;
BasicBlock::iterator InsertPt = BlockToInsertInto->getFirstNonPHI();
std::map<Instruction*, Value*> ExitValues;
// Find all values that are computed inside the loop, but used outside of it.
// Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
// the exit blocks of the loop to find them.
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
BasicBlock *ExitBB = ExitBlocks[i];
// If there are no PHI nodes in this exit block, then no values defined
// inside the loop are used on this path, skip it.
PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
if (!PN) continue;
unsigned NumPreds = PN->getNumIncomingValues();
// Iterate over all of the PHI nodes.
BasicBlock::iterator BBI = ExitBB->begin();
while ((PN = dyn_cast<PHINode>(BBI++))) {
if (PN->use_empty())
continue; // dead use, don't replace it
// Iterate over all of the values in all the PHI nodes.
for (unsigned i = 0; i != NumPreds; ++i) {
// If the value being merged in is not integer or is not defined
// in the loop, skip it.
Value *InVal = PN->getIncomingValue(i);
if (!isa<Instruction>(InVal) ||
// SCEV only supports integer expressions for now.
(!isa<IntegerType>(InVal->getType()) &&
!isa<PointerType>(InVal->getType())))
continue;
// If this pred is for a subloop, not L itself, skip it.
if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
continue; // The Block is in a subloop, skip it.
// Check that InVal is defined in the loop.
Instruction *Inst = cast<Instruction>(InVal);
if (!L->contains(Inst->getParent()))
continue;
// Okay, this instruction has a user outside of the current loop
// and varies predictably *inside* the loop. Evaluate the value it
// contains when the loop exits, if possible.
SCEVHandle ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
if (!ExitValue->isLoopInvariant(L))
continue;
Changed = true;
++NumReplaced;
// See if we already computed the exit value for the instruction, if so,
// just reuse it.
Value *&ExitVal = ExitValues[Inst];
if (!ExitVal)
ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), InsertPt);
DOUT << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal
<< " LoopVal = " << *Inst << "\n";
PN->setIncomingValue(i, ExitVal);
// If this instruction is dead now, delete it.
RecursivelyDeleteTriviallyDeadInstructions(Inst);
// See if this is a single-entry LCSSA PHI node. If so, we can (and
// have to) remove
// the PHI entirely. This is safe, because the NewVal won't be variant
// in the loop, so we don't need an LCSSA phi node anymore.
if (NumPreds == 1) {
PN->replaceAllUsesWith(ExitVal);
RecursivelyDeleteTriviallyDeadInstructions(PN);
break;
}
}
}
}
}
void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
// First step. Check to see if there are any floating-point recurrences.
// If there are, change them into integer recurrences, permitting analysis by
// the SCEV routines.
//
BasicBlock *Header = L->getHeader();
SmallVector<WeakVH, 8> PHIs;
for (BasicBlock::iterator I = Header->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I)
PHIs.push_back(PN);
for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i]))
HandleFloatingPointIV(L, PN);
// If the loop previously had floating-point IV, ScalarEvolution
// may not have been able to compute a trip count. Now that we've done some
// re-writing, the trip count may be computable.
if (Changed)
SE->forgetLoopBackedgeTakenCount(L);
}
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
IU = &getAnalysis<IVUsers>();
LI = &getAnalysis<LoopInfo>();
SE = &getAnalysis<ScalarEvolution>();
Changed = false;
// If there are any floating-point recurrences, attempt to
// transform them to use integer recurrences.
RewriteNonIntegerIVs(L);
BasicBlock *Header = L->getHeader();
BasicBlock *ExitingBlock = L->getExitingBlock(); // may be null
SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L);
// Check to see if this loop has a computable loop-invariant execution count.
// If so, this means that we can compute the final value of any expressions
// that are recurrent in the loop, and substitute the exit values from the
// loop into any instructions outside of the loop that use the final values of
// the current expressions.
//
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
RewriteLoopExitValues(L, BackedgeTakenCount);
// Compute the type of the largest recurrence expression, and decide whether
// a canonical induction variable should be inserted.
const Type *LargestType = 0;
bool NeedCannIV = false;
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
LargestType = BackedgeTakenCount->getType();
LargestType = SE->getEffectiveSCEVType(LargestType);
// If we have a known trip count and a single exit block, we'll be
// rewriting the loop exit test condition below, which requires a
// canonical induction variable.
if (ExitingBlock)
NeedCannIV = true;
}
for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
SCEVHandle Stride = IU->StrideOrder[i];
const Type *Ty = SE->getEffectiveSCEVType(Stride->getType());
if (!LargestType ||
SE->getTypeSizeInBits(Ty) >
SE->getTypeSizeInBits(LargestType))
LargestType = Ty;
std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
IU->IVUsesByStride.find(IU->StrideOrder[i]);
assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
if (!SI->second->Users.empty())
NeedCannIV = true;
}
// Create a rewriter object which we'll use to transform the code with.
SCEVExpander Rewriter(*SE);
// Now that we know the largest of of the induction variable expressions
// in this loop, insert a canonical induction variable of the largest size.
Value *IndVar = 0;
if (NeedCannIV) {
IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
++NumInserted;
Changed = true;
DOUT << "INDVARS: New CanIV: " << *IndVar;
}
// If we have a trip count expression, rewrite the loop's exit condition
// using it. We can currently only handle loops with a single exit.
ICmpInst *NewICmp = 0;
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) && ExitingBlock) {
assert(NeedCannIV &&
"LinearFunctionTestReplace requires a canonical induction variable");
// Can't rewrite non-branch yet.
if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()))
NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
ExitingBlock, BI, Rewriter);
}
Rewriter.setInsertionPoint(Header->getFirstNonPHI());
// Rewrite IV-derived expressions. Clears the rewriter cache.
RewriteIVExpressions(L, LargestType, Rewriter);
// The Rewriter may only be used for isInsertedInstruction queries from this
// point on.
// Loop-invariant instructions in the preheader that aren't used in the
// loop may be sunk below the loop to reduce register pressure.
SinkUnusedInvariants(L, Rewriter);
// Reorder instructions to avoid use-before-def conditions.
FixUsesBeforeDefs(L, Rewriter);
// For completeness, inform IVUsers of the IV use in the newly-created
// loop exit test instruction.
if (NewICmp)
IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0)));
// Clean up dead instructions.
DeleteDeadPHIs(L->getHeader());
// Check a post-condition.
assert(L->isLCSSAForm() && "Indvars did not leave the loop in lcssa form!");
return Changed;
}
void IndVarSimplify::RewriteIVExpressions(Loop *L, const Type *LargestType,
SCEVExpander &Rewriter) {
SmallVector<WeakVH, 16> DeadInsts;
// Rewrite all induction variable expressions in terms of the canonical
// induction variable.
//
// If there were induction variables of other sizes or offsets, manually
// add the offsets to the primary induction variable and cast, avoiding
// the need for the code evaluation methods to insert induction variables
// of different sizes.
for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
SCEVHandle Stride = IU->StrideOrder[i];
std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
IU->IVUsesByStride.find(IU->StrideOrder[i]);
assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
ilist<IVStrideUse> &List = SI->second->Users;
for (ilist<IVStrideUse>::iterator UI = List.begin(),
E = List.end(); UI != E; ++UI) {
SCEVHandle Offset = UI->getOffset();
Value *Op = UI->getOperandValToReplace();
Instruction *User = UI->getUser();
bool isSigned = UI->isSigned();
// Compute the final addrec to expand into code.
SCEVHandle AR = IU->getReplacementExpr(*UI);
// FIXME: It is an extremely bad idea to indvar substitute anything more
// complex than affine induction variables. Doing so will put expensive
// polynomial evaluations inside of the loop, and the str reduction pass
// currently can only reduce affine polynomials. For now just disable
// indvar subst on anything more complex than an affine addrec, unless
// it can be expanded to a trivial value.
if (!Stride->isLoopInvariant(L) &&
!isa<SCEVConstant>(AR) &&
L->contains(User->getParent()))
continue;
Value *NewVal = 0;
if (AR->isLoopInvariant(L)) {
BasicBlock::iterator I = Rewriter.getInsertionPoint();
// Expand loop-invariant values in the loop preheader. They will
// be sunk to the exit block later, if possible.
NewVal =
Rewriter.expandCodeFor(AR, LargestType,
L->getLoopPreheader()->getTerminator());
Rewriter.setInsertionPoint(I);
++NumReplaced;
} else {
const Type *IVTy = Offset->getType();
const Type *UseTy = Op->getType();
// Promote the Offset and Stride up to the canonical induction
// variable's bit width.
SCEVHandle PromotedOffset = Offset;
SCEVHandle PromotedStride = Stride;
if (SE->getTypeSizeInBits(IVTy) != SE->getTypeSizeInBits(LargestType)) {
// It doesn't matter for correctness whether zero or sign extension
// is used here, since the value is truncated away below, but if the
// value is signed, sign extension is more likely to be folded.
if (isSigned) {
PromotedOffset = SE->getSignExtendExpr(PromotedOffset, LargestType);
PromotedStride = SE->getSignExtendExpr(PromotedStride, LargestType);
} else {
PromotedOffset = SE->getZeroExtendExpr(PromotedOffset, LargestType);
// If the stride is obviously negative, use sign extension to
// produce things like x-1 instead of x+255.
if (isa<SCEVConstant>(PromotedStride) &&
cast<SCEVConstant>(PromotedStride)
->getValue()->getValue().isNegative())
PromotedStride = SE->getSignExtendExpr(PromotedStride,
LargestType);
else
PromotedStride = SE->getZeroExtendExpr(PromotedStride,
LargestType);
}
}
// Create the SCEV representing the offset from the canonical
// induction variable, still in the canonical induction variable's
// type, so that all expanded arithmetic is done in the same type.
SCEVHandle NewAR = SE->getAddRecExpr(SE->getIntegerSCEV(0, LargestType),
PromotedStride, L);
// Add the PromotedOffset as a separate step, because it may not be
// loop-invariant.
NewAR = SE->getAddExpr(NewAR, PromotedOffset);
// Expand the addrec into instructions.
Value *V = Rewriter.expandCodeFor(NewAR);
// Insert an explicit cast if necessary to truncate the value
// down to the original stride type. This is done outside of
// SCEVExpander because in SCEV expressions, a truncate of an
// addrec is always folded.
if (LargestType != IVTy) {
if (SE->getTypeSizeInBits(IVTy) != SE->getTypeSizeInBits(LargestType))
NewAR = SE->getTruncateExpr(NewAR, IVTy);
if (Rewriter.isInsertedExpression(NewAR))
V = Rewriter.expandCodeFor(NewAR);
else {
V = Rewriter.InsertCastOfTo(CastInst::getCastOpcode(V, false,
IVTy, false),
V, IVTy);
assert(!isa<SExtInst>(V) && !isa<ZExtInst>(V) &&
"LargestType wasn't actually the largest type!");
// Force the rewriter to use this trunc whenever this addrec
// appears so that it doesn't insert new phi nodes or
// arithmetic in a different type.
Rewriter.addInsertedValue(V, NewAR);
}
}
DOUT << "INDVARS: Made offset-and-trunc IV for offset "
<< *IVTy << " " << *Offset << ": ";
DEBUG(WriteAsOperand(*DOUT, V, false));
DOUT << "\n";
// Now expand it into actual Instructions and patch it into place.
NewVal = Rewriter.expandCodeFor(AR, UseTy);
}
// Patch the new value into place.
if (Op->hasName())
NewVal->takeName(Op);
User->replaceUsesOfWith(Op, NewVal);
UI->setOperandValToReplace(NewVal);
DOUT << "INDVARS: Rewrote IV '" << *AR << "' " << *Op
<< " into = " << *NewVal << "\n";
++NumRemoved;
Changed = true;
// The old value may be dead now.
DeadInsts.push_back(Op);
}
}
// Clear the rewriter cache, because values that are in the rewriter's cache
// can be deleted in the loop below, causing the AssertingVH in the cache to
// trigger.
Rewriter.clear();
// Now that we're done iterating through lists, clean up any instructions
// which are now dead.
while (!DeadInsts.empty()) {
Instruction *Inst = dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val());
if (Inst)
RecursivelyDeleteTriviallyDeadInstructions(Inst);
}
}
/// If there's a single exit block, sink any loop-invariant values that
/// were defined in the preheader but not used inside the loop into the
/// exit block to reduce register pressure in the loop.
void IndVarSimplify::SinkUnusedInvariants(Loop *L, SCEVExpander &Rewriter) {
BasicBlock *ExitBlock = L->getExitBlock();
if (!ExitBlock) return;
Instruction *NonPHI = ExitBlock->getFirstNonPHI();
BasicBlock *Preheader = L->getLoopPreheader();
BasicBlock::iterator I = Preheader->getTerminator();
while (I != Preheader->begin()) {
--I;
// New instructions were inserted at the end of the preheader. Only
// consider those new instructions.
if (!Rewriter.isInsertedInstruction(I))
break;
// Determine if there is a use in or before the loop (direct or
// otherwise).
bool UsedInLoop = false;
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
UI != UE; ++UI) {
BasicBlock *UseBB = cast<Instruction>(UI)->getParent();
if (PHINode *P = dyn_cast<PHINode>(UI)) {
unsigned i =
PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
UseBB = P->getIncomingBlock(i);
}
if (UseBB == Preheader || L->contains(UseBB)) {
UsedInLoop = true;
break;
}
}
// If there is, the def must remain in the preheader.
if (UsedInLoop)
continue;
// Otherwise, sink it to the exit block.
Instruction *ToMove = I;
bool Done = false;
if (I != Preheader->begin())
--I;
else
Done = true;
ToMove->moveBefore(NonPHI);
if (Done)
break;
}
}
/// Re-schedule the inserted instructions to put defs before uses. This
/// fixes problems that arrise when SCEV expressions contain loop-variant
/// values unrelated to the induction variable which are defined inside the
/// loop. FIXME: It would be better to insert instructions in the right
/// place so that this step isn't needed.
void IndVarSimplify::FixUsesBeforeDefs(Loop *L, SCEVExpander &Rewriter) {
// Visit all the blocks in the loop in pre-order dom-tree dfs order.
DominatorTree *DT = &getAnalysis<DominatorTree>();
std::map<Instruction *, unsigned> NumPredsLeft;
SmallVector<DomTreeNode *, 16> Worklist;
Worklist.push_back(DT->getNode(L->getHeader()));
do {
DomTreeNode *Node = Worklist.pop_back_val();
for (DomTreeNode::iterator I = Node->begin(), E = Node->end(); I != E; ++I)
if (L->contains((*I)->getBlock()))
Worklist.push_back(*I);
BasicBlock *BB = Node->getBlock();
// Visit all the instructions in the block top down.
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
// Count the number of operands that aren't properly dominating.
unsigned NumPreds = 0;
if (Rewriter.isInsertedInstruction(I) && !isa<PHINode>(I))
for (User::op_iterator OI = I->op_begin(), OE = I->op_end();
OI != OE; ++OI)
if (Instruction *Inst = dyn_cast<Instruction>(OI))
if (L->contains(Inst->getParent()) && !NumPredsLeft.count(Inst))
++NumPreds;
NumPredsLeft[I] = NumPreds;
// Notify uses of the position of this instruction, and move the
// users (and their dependents, recursively) into place after this
// instruction if it is their last outstanding operand.
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
UI != UE; ++UI) {
Instruction *Inst = cast<Instruction>(UI);
std::map<Instruction *, unsigned>::iterator Z = NumPredsLeft.find(Inst);
if (Z != NumPredsLeft.end() && Z->second != 0 && --Z->second == 0) {
SmallVector<Instruction *, 4> UseWorkList;
UseWorkList.push_back(Inst);
BasicBlock::iterator InsertPt = I;
if (InvokeInst *II = dyn_cast<InvokeInst>(InsertPt))
InsertPt = II->getNormalDest()->begin();
else
++InsertPt;
while (isa<PHINode>(InsertPt)) ++InsertPt;
do {
Instruction *Use = UseWorkList.pop_back_val();
Use->moveBefore(InsertPt);
NumPredsLeft.erase(Use);
for (Value::use_iterator IUI = Use->use_begin(),
IUE = Use->use_end(); IUI != IUE; ++IUI) {
Instruction *IUIInst = cast<Instruction>(IUI);
if (L->contains(IUIInst->getParent()) &&
Rewriter.isInsertedInstruction(IUIInst) &&
!isa<PHINode>(IUIInst))
UseWorkList.push_back(IUIInst);
}
} while (!UseWorkList.empty());
}
}
}
} while (!Worklist.empty());
}
/// Return true if it is OK to use SIToFPInst for an inducation variable
/// with given inital and exit values.
static bool useSIToFPInst(ConstantFP &InitV, ConstantFP &ExitV,
uint64_t intIV, uint64_t intEV) {
if (InitV.getValueAPF().isNegative() || ExitV.getValueAPF().isNegative())
return true;
// If the iteration range can be handled by SIToFPInst then use it.
APInt Max = APInt::getSignedMaxValue(32);
if (Max.getZExtValue() > static_cast<uint64_t>(abs64(intEV - intIV)))
return true;
return false;
}
/// convertToInt - Convert APF to an integer, if possible.
static bool convertToInt(const APFloat &APF, uint64_t *intVal) {
bool isExact = false;
if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
return false;
if (APF.convertToInteger(intVal, 32, APF.isNegative(),
APFloat::rmTowardZero, &isExact)
!= APFloat::opOK)
return false;
if (!isExact)
return false;
return true;
}
/// HandleFloatingPointIV - If the loop has floating induction variable
/// then insert corresponding integer induction variable if possible.
/// For example,
/// for(double i = 0; i < 10000; ++i)
/// bar(i)
/// is converted into
/// for(int i = 0; i < 10000; ++i)
/// bar((double)i);
///
void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PH) {
unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0));
unsigned BackEdge = IncomingEdge^1;
// Check incoming value.
ConstantFP *InitValue = dyn_cast<ConstantFP>(PH->getIncomingValue(IncomingEdge));
if (!InitValue) return;
uint64_t newInitValue = Type::Int32Ty->getPrimitiveSizeInBits();
if (!convertToInt(InitValue->getValueAPF(), &newInitValue))
return;
// Check IV increment. Reject this PH if increement operation is not
// an add or increment value can not be represented by an integer.
BinaryOperator *Incr =
dyn_cast<BinaryOperator>(PH->getIncomingValue(BackEdge));
if (!Incr) return;
if (Incr->getOpcode() != Instruction::Add) return;
ConstantFP *IncrValue = NULL;
unsigned IncrVIndex = 1;
if (Incr->getOperand(1) == PH)
IncrVIndex = 0;
IncrValue = dyn_cast<ConstantFP>(Incr->getOperand(IncrVIndex));
if (!IncrValue) return;
uint64_t newIncrValue = Type::Int32Ty->getPrimitiveSizeInBits();
if (!convertToInt(IncrValue->getValueAPF(), &newIncrValue))
return;
// Check Incr uses. One user is PH and the other users is exit condition used
// by the conditional terminator.
Value::use_iterator IncrUse = Incr->use_begin();
Instruction *U1 = cast<Instruction>(IncrUse++);
if (IncrUse == Incr->use_end()) return;
Instruction *U2 = cast<Instruction>(IncrUse++);
if (IncrUse != Incr->use_end()) return;
// Find exit condition.
FCmpInst *EC = dyn_cast<FCmpInst>(U1);
if (!EC)
EC = dyn_cast<FCmpInst>(U2);
if (!EC) return;
if (BranchInst *BI = dyn_cast<BranchInst>(EC->getParent()->getTerminator())) {
if (!BI->isConditional()) return;
if (BI->getCondition() != EC) return;
}
// Find exit value. If exit value can not be represented as an interger then
// do not handle this floating point PH.
ConstantFP *EV = NULL;
unsigned EVIndex = 1;
if (EC->getOperand(1) == Incr)
EVIndex = 0;
EV = dyn_cast<ConstantFP>(EC->getOperand(EVIndex));
if (!EV) return;
uint64_t intEV = Type::Int32Ty->getPrimitiveSizeInBits();
if (!convertToInt(EV->getValueAPF(), &intEV))
return;
// Find new predicate for integer comparison.
CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
switch (EC->getPredicate()) {
case CmpInst::FCMP_OEQ:
case CmpInst::FCMP_UEQ:
NewPred = CmpInst::ICMP_EQ;
break;
case CmpInst::FCMP_OGT:
case CmpInst::FCMP_UGT:
NewPred = CmpInst::ICMP_UGT;
break;
case CmpInst::FCMP_OGE:
case CmpInst::FCMP_UGE:
NewPred = CmpInst::ICMP_UGE;
break;
case CmpInst::FCMP_OLT:
case CmpInst::FCMP_ULT:
NewPred = CmpInst::ICMP_ULT;
break;
case CmpInst::FCMP_OLE:
case CmpInst::FCMP_ULE:
NewPred = CmpInst::ICMP_ULE;
break;
default:
break;
}
if (NewPred == CmpInst::BAD_ICMP_PREDICATE) return;
// Insert new integer induction variable.
PHINode *NewPHI = PHINode::Create(Type::Int32Ty,
PH->getName()+".int", PH);
NewPHI->addIncoming(ConstantInt::get(Type::Int32Ty, newInitValue),
PH->getIncomingBlock(IncomingEdge));
Value *NewAdd = BinaryOperator::CreateAdd(NewPHI,
ConstantInt::get(Type::Int32Ty,
newIncrValue),
Incr->getName()+".int", Incr);
NewPHI->addIncoming(NewAdd, PH->getIncomingBlock(BackEdge));
// The back edge is edge 1 of newPHI, whatever it may have been in the
// original PHI.
ConstantInt *NewEV = ConstantInt::get(Type::Int32Ty, intEV);
Value *LHS = (EVIndex == 1 ? NewPHI->getIncomingValue(1) : NewEV);
Value *RHS = (EVIndex == 1 ? NewEV : NewPHI->getIncomingValue(1));
ICmpInst *NewEC = new ICmpInst(NewPred, LHS, RHS, EC->getNameStart(),
EC->getParent()->getTerminator());
// In the following deltions, PH may become dead and may be deleted.
// Use a WeakVH to observe whether this happens.
WeakVH WeakPH = PH;
// Delete old, floating point, exit comparision instruction.
NewEC->takeName(EC);
EC->replaceAllUsesWith(NewEC);
RecursivelyDeleteTriviallyDeadInstructions(EC);
// Delete old, floating point, increment instruction.
Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
RecursivelyDeleteTriviallyDeadInstructions(Incr);
// Replace floating induction variable, if it isn't already deleted.
// Give SIToFPInst preference over UIToFPInst because it is faster on
// platforms that are widely used.
if (WeakPH && !PH->use_empty()) {
if (useSIToFPInst(*InitValue, *EV, newInitValue, intEV)) {
SIToFPInst *Conv = new SIToFPInst(NewPHI, PH->getType(), "indvar.conv",
PH->getParent()->getFirstNonPHI());
PH->replaceAllUsesWith(Conv);
} else {
UIToFPInst *Conv = new UIToFPInst(NewPHI, PH->getType(), "indvar.conv",
PH->getParent()->getFirstNonPHI());
PH->replaceAllUsesWith(Conv);
}
RecursivelyDeleteTriviallyDeadInstructions(PH);
}
// Add a new IVUsers entry for the newly-created integer PHI.
IU->AddUsersIfInteresting(NewPHI);
}
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