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llvm-6502/lib/Analysis/ScalarEvolutionExpander.cpp
Dan Gohman 278b49af8a Create ConstantExpr GEPs the correct way. This fixes 
MultiSource/Benchmarks/Prolangs-C/football and a variety of other
failures.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72120 91177308-0d34-0410-b5e6-96231b3b80d8
2009-05-19 19:18:01 +00:00

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//===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the implementation of the scalar evolution expander,
// which is used to generate the code corresponding to a given scalar evolution
// expression.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Target/TargetData.h"
using namespace llvm;
/// InsertCastOfTo - Insert a cast of V to the specified type, doing what
/// we can to share the casts.
Value *SCEVExpander::InsertCastOfTo(Instruction::CastOps opcode, Value *V,
const Type *Ty) {
// Short-circuit unnecessary bitcasts.
if (opcode == Instruction::BitCast && V->getType() == Ty)
return V;
// Short-circuit unnecessary inttoptr<->ptrtoint casts.
if ((opcode == Instruction::PtrToInt || opcode == Instruction::IntToPtr) &&
SE.getTypeSizeInBits(Ty) == SE.getTypeSizeInBits(V->getType())) {
if (CastInst *CI = dyn_cast<CastInst>(V))
if ((CI->getOpcode() == Instruction::PtrToInt ||
CI->getOpcode() == Instruction::IntToPtr) &&
SE.getTypeSizeInBits(CI->getType()) ==
SE.getTypeSizeInBits(CI->getOperand(0)->getType()))
return CI->getOperand(0);
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
if ((CE->getOpcode() == Instruction::PtrToInt ||
CE->getOpcode() == Instruction::IntToPtr) &&
SE.getTypeSizeInBits(CE->getType()) ==
SE.getTypeSizeInBits(CE->getOperand(0)->getType()))
return CE->getOperand(0);
}
// FIXME: keep track of the cast instruction.
if (Constant *C = dyn_cast<Constant>(V))
return ConstantExpr::getCast(opcode, C, Ty);
if (Argument *A = dyn_cast<Argument>(V)) {
// Check to see if there is already a cast!
for (Value::use_iterator UI = A->use_begin(), E = A->use_end();
UI != E; ++UI) {
if ((*UI)->getType() == Ty)
if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI)))
if (CI->getOpcode() == opcode) {
// If the cast isn't the first instruction of the function, move it.
if (BasicBlock::iterator(CI) !=
A->getParent()->getEntryBlock().begin()) {
// If the CastInst is the insert point, change the insert point.
if (CI == InsertPt) ++InsertPt;
// Splice the cast at the beginning of the entry block.
CI->moveBefore(A->getParent()->getEntryBlock().begin());
}
return CI;
}
}
Instruction *I = CastInst::Create(opcode, V, Ty, V->getName(),
A->getParent()->getEntryBlock().begin());
InsertedValues.insert(I);
return I;
}
Instruction *I = cast<Instruction>(V);
// Check to see if there is already a cast. If there is, use it.
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
UI != E; ++UI) {
if ((*UI)->getType() == Ty)
if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI)))
if (CI->getOpcode() == opcode) {
BasicBlock::iterator It = I; ++It;
if (isa<InvokeInst>(I))
It = cast<InvokeInst>(I)->getNormalDest()->begin();
while (isa<PHINode>(It)) ++It;
if (It != BasicBlock::iterator(CI)) {
// If the CastInst is the insert point, change the insert point.
if (CI == InsertPt) ++InsertPt;
// Splice the cast immediately after the operand in question.
CI->moveBefore(It);
}
return CI;
}
}
BasicBlock::iterator IP = I; ++IP;
if (InvokeInst *II = dyn_cast<InvokeInst>(I))
IP = II->getNormalDest()->begin();
while (isa<PHINode>(IP)) ++IP;
Instruction *CI = CastInst::Create(opcode, V, Ty, V->getName(), IP);
InsertedValues.insert(CI);
return CI;
}
/// InsertNoopCastOfTo - Insert a cast of V to the specified type,
/// which must be possible with a noop cast.
Value *SCEVExpander::InsertNoopCastOfTo(Value *V, const Type *Ty) {
Instruction::CastOps Op = CastInst::getCastOpcode(V, false, Ty, false);
assert((Op == Instruction::BitCast ||
Op == Instruction::PtrToInt ||
Op == Instruction::IntToPtr) &&
"InsertNoopCastOfTo cannot perform non-noop casts!");
assert(SE.getTypeSizeInBits(V->getType()) == SE.getTypeSizeInBits(Ty) &&
"InsertNoopCastOfTo cannot change sizes!");
return InsertCastOfTo(Op, V, Ty);
}
/// InsertBinop - Insert the specified binary operator, doing a small amount
/// of work to avoid inserting an obviously redundant operation.
Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, Value *LHS,
Value *RHS, BasicBlock::iterator InsertPt) {
// Fold a binop with constant operands.
if (Constant *CLHS = dyn_cast<Constant>(LHS))
if (Constant *CRHS = dyn_cast<Constant>(RHS))
return ConstantExpr::get(Opcode, CLHS, CRHS);
// Do a quick scan to see if we have this binop nearby. If so, reuse it.
unsigned ScanLimit = 6;
BasicBlock::iterator BlockBegin = InsertPt->getParent()->begin();
if (InsertPt != BlockBegin) {
// Scanning starts from the last instruction before InsertPt.
BasicBlock::iterator IP = InsertPt;
--IP;
for (; ScanLimit; --IP, --ScanLimit) {
if (IP->getOpcode() == (unsigned)Opcode && IP->getOperand(0) == LHS &&
IP->getOperand(1) == RHS)
return IP;
if (IP == BlockBegin) break;
}
}
// If we haven't found this binop, insert it.
Instruction *BO = BinaryOperator::Create(Opcode, LHS, RHS, "tmp", InsertPt);
InsertedValues.insert(BO);
return BO;
}
/// expandAddToGEP - Expand a SCEVAddExpr with a pointer type into a GEP
/// instead of using ptrtoint+arithmetic+inttoptr.
Value *SCEVExpander::expandAddToGEP(const SCEVAddExpr *S,
const PointerType *PTy,
const Type *Ty,
Value *V) {
const Type *ElTy = PTy->getElementType();
SmallVector<Value *, 4> GepIndices;
std::vector<SCEVHandle> Ops = S->getOperands();
bool AnyNonZeroIndices = false;
Ops.pop_back();
// Decend down the pointer's type and attempt to convert the other
// operands into GEP indices, at each level. The first index in a GEP
// indexes into the array implied by the pointer operand; the rest of
// the indices index into the element or field type selected by the
// preceding index.
for (;;) {
APInt ElSize = APInt(SE.getTypeSizeInBits(Ty),
ElTy->isSized() ? SE.TD->getTypeAllocSize(ElTy) : 0);
std::vector<SCEVHandle> NewOps;
std::vector<SCEVHandle> ScaledOps;
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
if (ElSize != 0) {
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(Ops[i]))
if (!C->getValue()->getValue().srem(ElSize)) {
ConstantInt *CI =
ConstantInt::get(C->getValue()->getValue().sdiv(ElSize));
SCEVHandle Div = SE.getConstant(CI);
ScaledOps.push_back(Div);
continue;
}
if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(Ops[i]))
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(M->getOperand(0)))
if (C->getValue()->getValue() == ElSize) {
for (unsigned j = 1, f = M->getNumOperands(); j != f; ++j)
ScaledOps.push_back(M->getOperand(j));
continue;
}
if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(Ops[i]))
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getValue()))
if (BO->getOpcode() == Instruction::Mul)
if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1)))
if (CI->getValue() == ElSize) {
ScaledOps.push_back(SE.getUnknown(BO->getOperand(0)));
continue;
}
if (ElSize == 1) {
ScaledOps.push_back(Ops[i]);
continue;
}
}
NewOps.push_back(Ops[i]);
}
Ops = NewOps;
AnyNonZeroIndices |= !ScaledOps.empty();
Value *Scaled = ScaledOps.empty() ?
Constant::getNullValue(Ty) :
expandCodeFor(SE.getAddExpr(ScaledOps), Ty);
GepIndices.push_back(Scaled);
// Collect struct field index operands.
if (!Ops.empty())
while (const StructType *STy = dyn_cast<StructType>(ElTy)) {
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(Ops[0]))
if (SE.getTypeSizeInBits(C->getType()) <= 64) {
const StructLayout &SL = *SE.TD->getStructLayout(STy);
uint64_t FullOffset = C->getValue()->getZExtValue();
if (FullOffset < SL.getSizeInBytes()) {
unsigned ElIdx = SL.getElementContainingOffset(FullOffset);
GepIndices.push_back(ConstantInt::get(Type::Int32Ty, ElIdx));
ElTy = STy->getTypeAtIndex(ElIdx);
Ops[0] =
SE.getConstant(ConstantInt::get(Ty,
FullOffset -
SL.getElementOffset(ElIdx)));
AnyNonZeroIndices = true;
continue;
}
}
break;
}
if (const ArrayType *ATy = dyn_cast<ArrayType>(ElTy)) {
ElTy = ATy->getElementType();
continue;
}
break;
}
// If none of the operands were convertable to proper GEP indices, cast
// the base to i8* and do an ugly getelementptr with that. It's still
// better than ptrtoint+arithmetic+inttoptr at least.
if (!AnyNonZeroIndices) {
V = InsertNoopCastOfTo(V,
Type::Int8Ty->getPointerTo(PTy->getAddressSpace()));
Value *Idx = expand(SE.getAddExpr(Ops));
Idx = InsertNoopCastOfTo(Idx, Ty);
// Fold a GEP with constant operands.
if (Constant *CLHS = dyn_cast<Constant>(V))
if (Constant *CRHS = dyn_cast<Constant>(Idx))
return ConstantExpr::getGetElementPtr(CLHS, &CRHS, 1);
// Do a quick scan to see if we have this GEP nearby. If so, reuse it.
unsigned ScanLimit = 6;
BasicBlock::iterator BlockBegin = InsertPt->getParent()->begin();
if (InsertPt != BlockBegin) {
// Scanning starts from the last instruction before InsertPt.
BasicBlock::iterator IP = InsertPt;
--IP;
for (; ScanLimit; --IP, --ScanLimit) {
if (IP->getOpcode() == Instruction::GetElementPtr &&
IP->getOperand(0) == V && IP->getOperand(1) == Idx)
return IP;
if (IP == BlockBegin) break;
}
}
Value *GEP = GetElementPtrInst::Create(V, Idx, "scevgep", InsertPt);
InsertedValues.insert(GEP);
return GEP;
}
// Insert a pretty getelementptr.
Value *GEP = GetElementPtrInst::Create(V,
GepIndices.begin(),
GepIndices.end(),
"scevgep", InsertPt);
Ops.push_back(SE.getUnknown(GEP));
InsertedValues.insert(GEP);
return expand(SE.getAddExpr(Ops));
}
Value *SCEVExpander::visitAddExpr(const SCEVAddExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
Value *V = expand(S->getOperand(S->getNumOperands()-1));
// Turn things like ptrtoint+arithmetic+inttoptr into GEP. This helps
// BasicAliasAnalysis analyze the result. However, it suffers from the
// underlying bug described in PR2831. Addition in LLVM currently always
// has two's complement wrapping guaranteed. However, the semantics for
// getelementptr overflow are ambiguous. In the common case though, this
// expansion gets used when a GEP in the original code has been converted
// into integer arithmetic, in which case the resulting code will be no
// more undefined than it was originally.
if (SE.TD)
if (const PointerType *PTy = dyn_cast<PointerType>(V->getType()))
return expandAddToGEP(S, PTy, Ty, V);
V = InsertNoopCastOfTo(V, Ty);
// Emit a bunch of add instructions
for (int i = S->getNumOperands()-2; i >= 0; --i) {
Value *W = expand(S->getOperand(i));
W = InsertNoopCastOfTo(W, Ty);
V = InsertBinop(Instruction::Add, V, W, InsertPt);
}
return V;
}
Value *SCEVExpander::visitMulExpr(const SCEVMulExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
int FirstOp = 0; // Set if we should emit a subtract.
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
if (SC->getValue()->isAllOnesValue())
FirstOp = 1;
int i = S->getNumOperands()-2;
Value *V = expand(S->getOperand(i+1));
V = InsertNoopCastOfTo(V, Ty);
// Emit a bunch of multiply instructions
for (; i >= FirstOp; --i) {
Value *W = expand(S->getOperand(i));
W = InsertNoopCastOfTo(W, Ty);
V = InsertBinop(Instruction::Mul, V, W, InsertPt);
}
// -1 * ... ---> 0 - ...
if (FirstOp == 1)
V = InsertBinop(Instruction::Sub, Constant::getNullValue(Ty), V, InsertPt);
return V;
}
Value *SCEVExpander::visitUDivExpr(const SCEVUDivExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
Value *LHS = expand(S->getLHS());
LHS = InsertNoopCastOfTo(LHS, Ty);
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getRHS())) {
const APInt &RHS = SC->getValue()->getValue();
if (RHS.isPowerOf2())
return InsertBinop(Instruction::LShr, LHS,
ConstantInt::get(Ty, RHS.logBase2()),
InsertPt);
}
Value *RHS = expand(S->getRHS());
RHS = InsertNoopCastOfTo(RHS, Ty);
return InsertBinop(Instruction::UDiv, LHS, RHS, InsertPt);
}
Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
const Loop *L = S->getLoop();
// {X,+,F} --> X + {0,+,F}
if (!S->getStart()->isZero()) {
std::vector<SCEVHandle> NewOps(S->getOperands());
NewOps[0] = SE.getIntegerSCEV(0, Ty);
Value *Rest = expand(SE.getAddRecExpr(NewOps, L));
return expand(SE.getAddExpr(S->getStart(), SE.getUnknown(Rest)));
}
// {0,+,1} --> Insert a canonical induction variable into the loop!
if (S->isAffine() &&
S->getOperand(1) == SE.getIntegerSCEV(1, Ty)) {
// Create and insert the PHI node for the induction variable in the
// specified loop.
BasicBlock *Header = L->getHeader();
PHINode *PN = PHINode::Create(Ty, "indvar", Header->begin());
InsertedValues.insert(PN);
PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
pred_iterator HPI = pred_begin(Header);
assert(HPI != pred_end(Header) && "Loop with zero preds???");
if (!L->contains(*HPI)) ++HPI;
assert(HPI != pred_end(Header) && L->contains(*HPI) &&
"No backedge in loop?");
// Insert a unit add instruction right before the terminator corresponding
// to the back-edge.
Constant *One = ConstantInt::get(Ty, 1);
Instruction *Add = BinaryOperator::CreateAdd(PN, One, "indvar.next",
(*HPI)->getTerminator());
InsertedValues.insert(Add);
pred_iterator PI = pred_begin(Header);
if (*PI == L->getLoopPreheader())
++PI;
PN->addIncoming(Add, *PI);
return PN;
}
// Get the canonical induction variable I for this loop.
Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
// If this is a simple linear addrec, emit it now as a special case.
if (S->isAffine()) { // {0,+,F} --> i*F
Value *F = expand(S->getOperand(1));
F = InsertNoopCastOfTo(F, Ty);
// IF the step is by one, just return the inserted IV.
if (ConstantInt *CI = dyn_cast<ConstantInt>(F))
if (CI->getValue() == 1)
return I;
// If the insert point is directly inside of the loop, emit the multiply at
// the insert point. Otherwise, L is a loop that is a parent of the insert
// point loop. If we can, move the multiply to the outer most loop that it
// is safe to be in.
BasicBlock::iterator MulInsertPt = getInsertionPoint();
Loop *InsertPtLoop = SE.LI->getLoopFor(MulInsertPt->getParent());
if (InsertPtLoop != L && InsertPtLoop &&
L->contains(InsertPtLoop->getHeader())) {
do {
// If we cannot hoist the multiply out of this loop, don't.
if (!InsertPtLoop->isLoopInvariant(F)) break;
BasicBlock *InsertPtLoopPH = InsertPtLoop->getLoopPreheader();
// If this loop hasn't got a preheader, we aren't able to hoist the
// multiply.
if (!InsertPtLoopPH)
break;
// Otherwise, move the insert point to the preheader.
MulInsertPt = InsertPtLoopPH->getTerminator();
InsertPtLoop = InsertPtLoop->getParentLoop();
} while (InsertPtLoop != L);
}
return InsertBinop(Instruction::Mul, I, F, MulInsertPt);
}
// If this is a chain of recurrences, turn it into a closed form, using the
// folders, then expandCodeFor the closed form. This allows the folders to
// simplify the expression without having to build a bunch of special code
// into this folder.
SCEVHandle IH = SE.getUnknown(I); // Get I as a "symbolic" SCEV.
SCEVHandle V = S->evaluateAtIteration(IH, SE);
//cerr << "Evaluated: " << *this << "\n to: " << *V << "\n";
return expand(V);
}
Value *SCEVExpander::visitTruncateExpr(const SCEVTruncateExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
Value *V = expand(S->getOperand());
V = InsertNoopCastOfTo(V, SE.getEffectiveSCEVType(V->getType()));
Instruction *I = new TruncInst(V, Ty, "tmp.", InsertPt);
InsertedValues.insert(I);
return I;
}
Value *SCEVExpander::visitZeroExtendExpr(const SCEVZeroExtendExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
Value *V = expand(S->getOperand());
V = InsertNoopCastOfTo(V, SE.getEffectiveSCEVType(V->getType()));
Instruction *I = new ZExtInst(V, Ty, "tmp.", InsertPt);
InsertedValues.insert(I);
return I;
}
Value *SCEVExpander::visitSignExtendExpr(const SCEVSignExtendExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
Value *V = expand(S->getOperand());
V = InsertNoopCastOfTo(V, SE.getEffectiveSCEVType(V->getType()));
Instruction *I = new SExtInst(V, Ty, "tmp.", InsertPt);
InsertedValues.insert(I);
return I;
}
Value *SCEVExpander::visitSMaxExpr(const SCEVSMaxExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
Value *LHS = expand(S->getOperand(0));
LHS = InsertNoopCastOfTo(LHS, Ty);
for (unsigned i = 1; i < S->getNumOperands(); ++i) {
Value *RHS = expand(S->getOperand(i));
RHS = InsertNoopCastOfTo(RHS, Ty);
Instruction *ICmp =
new ICmpInst(ICmpInst::ICMP_SGT, LHS, RHS, "tmp", InsertPt);
InsertedValues.insert(ICmp);
Instruction *Sel = SelectInst::Create(ICmp, LHS, RHS, "smax", InsertPt);
InsertedValues.insert(Sel);
LHS = Sel;
}
return LHS;
}
Value *SCEVExpander::visitUMaxExpr(const SCEVUMaxExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
Value *LHS = expand(S->getOperand(0));
LHS = InsertNoopCastOfTo(LHS, Ty);
for (unsigned i = 1; i < S->getNumOperands(); ++i) {
Value *RHS = expand(S->getOperand(i));
RHS = InsertNoopCastOfTo(RHS, Ty);
Instruction *ICmp =
new ICmpInst(ICmpInst::ICMP_UGT, LHS, RHS, "tmp", InsertPt);
InsertedValues.insert(ICmp);
Instruction *Sel = SelectInst::Create(ICmp, LHS, RHS, "umax", InsertPt);
InsertedValues.insert(Sel);
LHS = Sel;
}
return LHS;
}
Value *SCEVExpander::expandCodeFor(SCEVHandle SH, const Type *Ty) {
// Expand the code for this SCEV.
Value *V = expand(SH);
if (Ty) {
assert(SE.getTypeSizeInBits(Ty) == SE.getTypeSizeInBits(SH->getType()) &&
"non-trivial casts should be done with the SCEVs directly!");
V = InsertNoopCastOfTo(V, Ty);
}
return V;
}
Value *SCEVExpander::expand(const SCEV *S) {
// Check to see if we already expanded this.
std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S);
if (I != InsertedExpressions.end())
return I->second;
Value *V = visit(S);
InsertedExpressions[S] = V;
return V;
}
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