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llvm-project/llvm/lib/Analysis/ScalarEvolutionExpander.cpp

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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"
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) {
// 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()) {
CI->moveBefore(A->getParent()->getEntryBlock().begin());
}
return CI;
}
}
return CastInst::Create(opcode, V, Ty, V->getName(),
A->getParent()->getEntryBlock().begin());
}
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)) {
// 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;
return CastInst::Create(opcode, V, Ty, V->getName(), IP);
}
/// 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, Instruction *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 (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(IP))
if (BinOp->getOpcode() == Opcode && BinOp->getOperand(0) == LHS &&
BinOp->getOperand(1) == RHS)
return BinOp;
if (IP == BlockBegin) break;
}
}
// If we haven't found this binop, insert it.
return BinaryOperator::Create(Opcode, LHS, RHS, "tmp", InsertPt);
}
Value *SCEVExpander::visitAddExpr(SCEVAddExpr *S) {
Value *V = expand(S->getOperand(S->getNumOperands()-1));
// Emit a bunch of add instructions
for (int i = S->getNumOperands()-2; i >= 0; --i)
V = InsertBinop(Instruction::Add, V, expand(S->getOperand(i)),
InsertPt);
return V;
}
Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) {
int FirstOp = 0; // Set if we should emit a subtract.
if (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));
// Emit a bunch of multiply instructions
for (; i >= FirstOp; --i)
V = InsertBinop(Instruction::Mul, V, expand(S->getOperand(i)),
InsertPt);
// -1 * ... ---> 0 - ...
if (FirstOp == 1)
V = InsertBinop(Instruction::Sub, Constant::getNullValue(V->getType()), V,
InsertPt);
return V;
}
Value *SCEVExpander::visitUDivExpr(SCEVUDivExpr *S) {
Value *LHS = expand(S->getLHS());
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getRHS())) {
const APInt &RHS = SC->getValue()->getValue();
if (RHS.isPowerOf2())
return InsertBinop(Instruction::LShr, LHS,
ConstantInt::get(S->getType(), RHS.logBase2()),
InsertPt);
}
Value *RHS = expand(S->getRHS());
return InsertBinop(Instruction::UDiv, LHS, RHS, InsertPt);
}
Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) {
const Type *Ty = S->getType();
const Loop *L = S->getLoop();
// We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F}
assert(Ty->isInteger() && "Cannot expand fp recurrences yet!");
// {X,+,F} --> X + {0,+,F}
if (!S->getStart()->isZero()) {
Value *Start = expand(S->getStart());
std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
NewOps[0] = SE.getIntegerSCEV(0, Ty);
Value *Rest = expand(SE.getAddRecExpr(NewOps, L));
// FIXME: look for an existing add to use.
return InsertBinop(Instruction::Add, Rest, Start, InsertPt);
}
// {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());
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());
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));
// 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.
Instruction *MulInsertPt = InsertPt;
Loop *InsertPtLoop = 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(SCEVTruncateExpr *S) {
Value *V = expand(S->getOperand());
return CastInst::CreateTruncOrBitCast(V, S->getType(), "tmp.", InsertPt);
}
Value *SCEVExpander::visitZeroExtendExpr(SCEVZeroExtendExpr *S) {
Value *V = expand(S->getOperand());
return CastInst::CreateZExtOrBitCast(V, S->getType(), "tmp.", InsertPt);
}
Value *SCEVExpander::visitSignExtendExpr(SCEVSignExtendExpr *S) {
Value *V = expand(S->getOperand());
return CastInst::CreateSExtOrBitCast(V, S->getType(), "tmp.", InsertPt);
}
Value *SCEVExpander::visitSMaxExpr(SCEVSMaxExpr *S) {
Value *LHS = expand(S->getOperand(0));
for (unsigned i = 1; i < S->getNumOperands(); ++i) {
Value *RHS = expand(S->getOperand(i));
Value *ICmp = new ICmpInst(ICmpInst::ICMP_SGT, LHS, RHS, "tmp", InsertPt);
LHS = SelectInst::Create(ICmp, LHS, RHS, "smax", InsertPt);
}
return LHS;
}
Value *SCEVExpander::visitUMaxExpr(SCEVUMaxExpr *S) {
Value *LHS = expand(S->getOperand(0));
for (unsigned i = 1; i < S->getNumOperands(); ++i) {
Value *RHS = expand(S->getOperand(i));
Value *ICmp = new ICmpInst(ICmpInst::ICMP_UGT, LHS, RHS, "tmp", InsertPt);
LHS = SelectInst::Create(ICmp, LHS, RHS, "umax", InsertPt);
}
return LHS;
}
Value *SCEVExpander::expandCodeFor(SCEVHandle SH, Instruction *IP) {
// Expand the code for this SCEV.
this->InsertPt = IP;
return expand(SH);
}
Value *SCEVExpander::expand(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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