llvm-6502/lib/Transforms/Scalar/CodeGenPrepare.cpp
Dale Johannesen 6603a1bff0 Don't generate branch to entry block.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36917 91177308-0d34-0410-b5e6-96231b3b80d8
2007-05-08 01:01:04 +00:00

931 lines
34 KiB
C++

//===- CodeGenPrepare.cpp - Prepare a function for code generation --------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Chris Lattner and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass munges the code in the input function to better prepare it for
// SelectionDAG-based code generation. This works around limitations in it's
// basic-block-at-a-time approach. It should eventually be removed.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "codegenprepare"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetAsmInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
using namespace llvm;
namespace {
class VISIBILITY_HIDDEN CodeGenPrepare : public FunctionPass {
/// TLI - Keep a pointer of a TargetLowering to consult for determining
/// transformation profitability.
const TargetLowering *TLI;
public:
static char ID; // Pass identification, replacement for typeid
CodeGenPrepare(const TargetLowering *tli = 0) : FunctionPass((intptr_t)&ID),
TLI(tli) {}
bool runOnFunction(Function &F);
private:
bool EliminateMostlyEmptyBlocks(Function &F);
bool CanMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const;
void EliminateMostlyEmptyBlock(BasicBlock *BB);
bool OptimizeBlock(BasicBlock &BB);
bool OptimizeLoadStoreInst(Instruction *I, Value *Addr,
const Type *AccessTy,
DenseMap<Value*,Value*> &SunkAddrs);
};
}
char CodeGenPrepare::ID = 0;
static RegisterPass<CodeGenPrepare> X("codegenprepare",
"Optimize for code generation");
FunctionPass *llvm::createCodeGenPreparePass(const TargetLowering *TLI) {
return new CodeGenPrepare(TLI);
}
bool CodeGenPrepare::runOnFunction(Function &F) {
bool EverMadeChange = false;
// First pass, eliminate blocks that contain only PHI nodes and an
// unconditional branch.
EverMadeChange |= EliminateMostlyEmptyBlocks(F);
bool MadeChange = true;
while (MadeChange) {
MadeChange = false;
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
MadeChange |= OptimizeBlock(*BB);
EverMadeChange |= MadeChange;
}
return EverMadeChange;
}
/// EliminateMostlyEmptyBlocks - eliminate blocks that contain only PHI nodes
/// and an unconditional branch. Passes before isel (e.g. LSR/loopsimplify)
/// often split edges in ways that are non-optimal for isel. Start by
/// eliminating these blocks so we can split them the way we want them.
bool CodeGenPrepare::EliminateMostlyEmptyBlocks(Function &F) {
bool MadeChange = false;
// Note that this intentionally skips the entry block.
for (Function::iterator I = ++F.begin(), E = F.end(); I != E; ) {
BasicBlock *BB = I++;
// If this block doesn't end with an uncond branch, ignore it.
BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
if (!BI || !BI->isUnconditional())
continue;
// If the instruction before the branch isn't a phi node, then other stuff
// is happening here.
BasicBlock::iterator BBI = BI;
if (BBI != BB->begin()) {
--BBI;
if (!isa<PHINode>(BBI)) continue;
}
// Do not break infinite loops.
BasicBlock *DestBB = BI->getSuccessor(0);
if (DestBB == BB)
continue;
if (!CanMergeBlocks(BB, DestBB))
continue;
EliminateMostlyEmptyBlock(BB);
MadeChange = true;
}
return MadeChange;
}
/// CanMergeBlocks - Return true if we can merge BB into DestBB if there is a
/// single uncond branch between them, and BB contains no other non-phi
/// instructions.
bool CodeGenPrepare::CanMergeBlocks(const BasicBlock *BB,
const BasicBlock *DestBB) const {
// We only want to eliminate blocks whose phi nodes are used by phi nodes in
// the successor. If there are more complex condition (e.g. preheaders),
// don't mess around with them.
BasicBlock::const_iterator BBI = BB->begin();
while (const PHINode *PN = dyn_cast<PHINode>(BBI++)) {
for (Value::use_const_iterator UI = PN->use_begin(), E = PN->use_end();
UI != E; ++UI) {
const Instruction *User = cast<Instruction>(*UI);
if (User->getParent() != DestBB || !isa<PHINode>(User))
return false;
// If User is inside DestBB block and it is a PHINode then check
// incoming value. If incoming value is not from BB then this is
// a complex condition (e.g. preheaders) we want to avoid here.
if (User->getParent() == DestBB) {
if (const PHINode *UPN = dyn_cast<PHINode>(User))
for (unsigned I = 0, E = UPN->getNumIncomingValues(); I != E; ++I) {
Instruction *Insn = dyn_cast<Instruction>(UPN->getIncomingValue(I));
if (Insn && Insn->getParent() == BB &&
Insn->getParent() != UPN->getIncomingBlock(I))
return false;
}
}
}
}
// If BB and DestBB contain any common predecessors, then the phi nodes in BB
// and DestBB may have conflicting incoming values for the block. If so, we
// can't merge the block.
const PHINode *DestBBPN = dyn_cast<PHINode>(DestBB->begin());
if (!DestBBPN) return true; // no conflict.
// Collect the preds of BB.
SmallPtrSet<BasicBlock*, 16> BBPreds;
if (const PHINode *BBPN = dyn_cast<PHINode>(BB->begin())) {
// It is faster to get preds from a PHI than with pred_iterator.
for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i)
BBPreds.insert(BBPN->getIncomingBlock(i));
} else {
BBPreds.insert(pred_begin(BB), pred_end(BB));
}
// Walk the preds of DestBB.
for (unsigned i = 0, e = DestBBPN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *Pred = DestBBPN->getIncomingBlock(i);
if (BBPreds.count(Pred)) { // Common predecessor?
BBI = DestBB->begin();
while (const PHINode *PN = dyn_cast<PHINode>(BBI++)) {
const Value *V1 = PN->getIncomingValueForBlock(Pred);
const Value *V2 = PN->getIncomingValueForBlock(BB);
// If V2 is a phi node in BB, look up what the mapped value will be.
if (const PHINode *V2PN = dyn_cast<PHINode>(V2))
if (V2PN->getParent() == BB)
V2 = V2PN->getIncomingValueForBlock(Pred);
// If there is a conflict, bail out.
if (V1 != V2) return false;
}
}
}
return true;
}
/// EliminateMostlyEmptyBlock - Eliminate a basic block that have only phi's and
/// an unconditional branch in it.
void CodeGenPrepare::EliminateMostlyEmptyBlock(BasicBlock *BB) {
BranchInst *BI = cast<BranchInst>(BB->getTerminator());
BasicBlock *DestBB = BI->getSuccessor(0);
DOUT << "MERGING MOSTLY EMPTY BLOCKS - BEFORE:\n" << *BB << *DestBB;
// If the destination block has a single pred, then this is a trivial edge,
// just collapse it.
if (DestBB->getSinglePredecessor()) {
// If DestBB has single-entry PHI nodes, fold them.
while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
PN->replaceAllUsesWith(PN->getIncomingValue(0));
PN->eraseFromParent();
}
// Splice all the PHI nodes from BB over to DestBB.
DestBB->getInstList().splice(DestBB->begin(), BB->getInstList(),
BB->begin(), BI);
// Anything that branched to BB now branches to DestBB.
BB->replaceAllUsesWith(DestBB);
// Nuke BB.
BB->eraseFromParent();
DOUT << "AFTER:\n" << *DestBB << "\n\n\n";
return;
}
// Otherwise, we have multiple predecessors of BB. Update the PHIs in DestBB
// to handle the new incoming edges it is about to have.
PHINode *PN;
for (BasicBlock::iterator BBI = DestBB->begin();
(PN = dyn_cast<PHINode>(BBI)); ++BBI) {
// Remove the incoming value for BB, and remember it.
Value *InVal = PN->removeIncomingValue(BB, false);
// Two options: either the InVal is a phi node defined in BB or it is some
// value that dominates BB.
PHINode *InValPhi = dyn_cast<PHINode>(InVal);
if (InValPhi && InValPhi->getParent() == BB) {
// Add all of the input values of the input PHI as inputs of this phi.
for (unsigned i = 0, e = InValPhi->getNumIncomingValues(); i != e; ++i)
PN->addIncoming(InValPhi->getIncomingValue(i),
InValPhi->getIncomingBlock(i));
} else {
// Otherwise, add one instance of the dominating value for each edge that
// we will be adding.
if (PHINode *BBPN = dyn_cast<PHINode>(BB->begin())) {
for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i)
PN->addIncoming(InVal, BBPN->getIncomingBlock(i));
} else {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
PN->addIncoming(InVal, *PI);
}
}
}
// The PHIs are now updated, change everything that refers to BB to use
// DestBB and remove BB.
BB->replaceAllUsesWith(DestBB);
BB->eraseFromParent();
DOUT << "AFTER:\n" << *DestBB << "\n\n\n";
}
/// SplitEdgeNicely - Split the critical edge from TI to it's specified
/// successor if it will improve codegen. We only do this if the successor has
/// phi nodes (otherwise critical edges are ok). If there is already another
/// predecessor of the succ that is empty (and thus has no phi nodes), use it
/// instead of introducing a new block.
static void SplitEdgeNicely(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
BasicBlock *TIBB = TI->getParent();
BasicBlock *Dest = TI->getSuccessor(SuccNum);
assert(isa<PHINode>(Dest->begin()) &&
"This should only be called if Dest has a PHI!");
/// TIPHIValues - This array is lazily computed to determine the values of
/// PHIs in Dest that TI would provide.
std::vector<Value*> TIPHIValues;
// Check to see if Dest has any blocks that can be used as a split edge for
// this terminator.
for (pred_iterator PI = pred_begin(Dest), E = pred_end(Dest); PI != E; ++PI) {
BasicBlock *Pred = *PI;
// To be usable, the pred has to end with an uncond branch to the dest.
BranchInst *PredBr = dyn_cast<BranchInst>(Pred->getTerminator());
if (!PredBr || !PredBr->isUnconditional() ||
// Must be empty other than the branch.
&Pred->front() != PredBr ||
// Cannot be the entry block; its label does not get emitted.
Pred == &(Dest->getParent()->getEntryBlock()))
continue;
// Finally, since we know that Dest has phi nodes in it, we have to make
// sure that jumping to Pred will have the same affect as going to Dest in
// terms of PHI values.
PHINode *PN;
unsigned PHINo = 0;
bool FoundMatch = true;
for (BasicBlock::iterator I = Dest->begin();
(PN = dyn_cast<PHINode>(I)); ++I, ++PHINo) {
if (PHINo == TIPHIValues.size())
TIPHIValues.push_back(PN->getIncomingValueForBlock(TIBB));
// If the PHI entry doesn't work, we can't use this pred.
if (TIPHIValues[PHINo] != PN->getIncomingValueForBlock(Pred)) {
FoundMatch = false;
break;
}
}
// If we found a workable predecessor, change TI to branch to Succ.
if (FoundMatch) {
Dest->removePredecessor(TIBB);
TI->setSuccessor(SuccNum, Pred);
return;
}
}
SplitCriticalEdge(TI, SuccNum, P, true);
}
/// OptimizeNoopCopyExpression - If the specified cast instruction is a noop
/// copy (e.g. it's casting from one pointer type to another, int->uint, or
/// int->sbyte on PPC), sink it into user blocks to reduce the number of virtual
/// registers that must be created and coallesced.
///
/// Return true if any changes are made.
static bool OptimizeNoopCopyExpression(CastInst *CI, const TargetLowering &TLI){
// If this is a noop copy,
MVT::ValueType SrcVT = TLI.getValueType(CI->getOperand(0)->getType());
MVT::ValueType DstVT = TLI.getValueType(CI->getType());
// This is an fp<->int conversion?
if (MVT::isInteger(SrcVT) != MVT::isInteger(DstVT))
return false;
// If this is an extension, it will be a zero or sign extension, which
// isn't a noop.
if (SrcVT < DstVT) return false;
// If these values will be promoted, find out what they will be promoted
// to. This helps us consider truncates on PPC as noop copies when they
// are.
if (TLI.getTypeAction(SrcVT) == TargetLowering::Promote)
SrcVT = TLI.getTypeToTransformTo(SrcVT);
if (TLI.getTypeAction(DstVT) == TargetLowering::Promote)
DstVT = TLI.getTypeToTransformTo(DstVT);
// If, after promotion, these are the same types, this is a noop copy.
if (SrcVT != DstVT)
return false;
BasicBlock *DefBB = CI->getParent();
/// InsertedCasts - Only insert a cast in each block once.
std::map<BasicBlock*, CastInst*> InsertedCasts;
bool MadeChange = false;
for (Value::use_iterator UI = CI->use_begin(), E = CI->use_end();
UI != E; ) {
Use &TheUse = UI.getUse();
Instruction *User = cast<Instruction>(*UI);
// Figure out which BB this cast is used in. For PHI's this is the
// appropriate predecessor block.
BasicBlock *UserBB = User->getParent();
if (PHINode *PN = dyn_cast<PHINode>(User)) {
unsigned OpVal = UI.getOperandNo()/2;
UserBB = PN->getIncomingBlock(OpVal);
}
// Preincrement use iterator so we don't invalidate it.
++UI;
// If this user is in the same block as the cast, don't change the cast.
if (UserBB == DefBB) continue;
// If we have already inserted a cast into this block, use it.
CastInst *&InsertedCast = InsertedCasts[UserBB];
if (!InsertedCast) {
BasicBlock::iterator InsertPt = UserBB->begin();
while (isa<PHINode>(InsertPt)) ++InsertPt;
InsertedCast =
CastInst::create(CI->getOpcode(), CI->getOperand(0), CI->getType(), "",
InsertPt);
MadeChange = true;
}
// Replace a use of the cast with a use of the new casat.
TheUse = InsertedCast;
}
// If we removed all uses, nuke the cast.
if (CI->use_empty())
CI->eraseFromParent();
return MadeChange;
}
/// EraseDeadInstructions - Erase any dead instructions
static void EraseDeadInstructions(Value *V) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I || !I->use_empty()) return;
SmallPtrSet<Instruction*, 16> Insts;
Insts.insert(I);
while (!Insts.empty()) {
I = *Insts.begin();
Insts.erase(I);
if (isInstructionTriviallyDead(I)) {
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
Insts.insert(U);
I->eraseFromParent();
}
}
}
/// ExtAddrMode - This is an extended version of TargetLowering::AddrMode which
/// holds actual Value*'s for register values.
struct ExtAddrMode : public TargetLowering::AddrMode {
Value *BaseReg;
Value *ScaledReg;
ExtAddrMode() : BaseReg(0), ScaledReg(0) {}
void dump() const;
};
static std::ostream &operator<<(std::ostream &OS, const ExtAddrMode &AM) {
bool NeedPlus = false;
OS << "[";
if (AM.BaseGV)
OS << (NeedPlus ? " + " : "")
<< "GV:%" << AM.BaseGV->getName(), NeedPlus = true;
if (AM.BaseOffs)
OS << (NeedPlus ? " + " : "") << AM.BaseOffs, NeedPlus = true;
if (AM.BaseReg)
OS << (NeedPlus ? " + " : "")
<< "Base:%" << AM.BaseReg->getName(), NeedPlus = true;
if (AM.Scale)
OS << (NeedPlus ? " + " : "")
<< AM.Scale << "*%" << AM.ScaledReg->getName(), NeedPlus = true;
return OS << "]";
}
void ExtAddrMode::dump() const {
cerr << *this << "\n";
}
static bool TryMatchingScaledValue(Value *ScaleReg, int64_t Scale,
const Type *AccessTy, ExtAddrMode &AddrMode,
SmallVector<Instruction*, 16> &AddrModeInsts,
const TargetLowering &TLI, unsigned Depth);
/// FindMaximalLegalAddressingMode - If we can, try to merge the computation of
/// Addr into the specified addressing mode. If Addr can't be added to AddrMode
/// this returns false. This assumes that Addr is either a pointer type or
/// intptr_t for the target.
static bool FindMaximalLegalAddressingMode(Value *Addr, const Type *AccessTy,
ExtAddrMode &AddrMode,
SmallVector<Instruction*, 16> &AddrModeInsts,
const TargetLowering &TLI,
unsigned Depth) {
// If this is a global variable, fold it into the addressing mode if possible.
if (GlobalValue *GV = dyn_cast<GlobalValue>(Addr)) {
if (AddrMode.BaseGV == 0) {
AddrMode.BaseGV = GV;
if (TLI.isLegalAddressingMode(AddrMode, AccessTy))
return true;
AddrMode.BaseGV = 0;
}
} else if (ConstantInt *CI = dyn_cast<ConstantInt>(Addr)) {
AddrMode.BaseOffs += CI->getSExtValue();
if (TLI.isLegalAddressingMode(AddrMode, AccessTy))
return true;
AddrMode.BaseOffs -= CI->getSExtValue();
} else if (isa<ConstantPointerNull>(Addr)) {
return true;
}
// Look through constant exprs and instructions.
unsigned Opcode = ~0U;
User *AddrInst = 0;
if (Instruction *I = dyn_cast<Instruction>(Addr)) {
Opcode = I->getOpcode();
AddrInst = I;
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Addr)) {
Opcode = CE->getOpcode();
AddrInst = CE;
}
// Limit recursion to avoid exponential behavior.
if (Depth == 5) { AddrInst = 0; Opcode = ~0U; }
// If this is really an instruction, add it to our list of related
// instructions.
if (Instruction *I = dyn_cast_or_null<Instruction>(AddrInst))
AddrModeInsts.push_back(I);
switch (Opcode) {
case Instruction::PtrToInt:
// PtrToInt is always a noop, as we know that the int type is pointer sized.
if (FindMaximalLegalAddressingMode(AddrInst->getOperand(0), AccessTy,
AddrMode, AddrModeInsts, TLI, Depth))
return true;
break;
case Instruction::IntToPtr:
// This inttoptr is a no-op if the integer type is pointer sized.
if (TLI.getValueType(AddrInst->getOperand(0)->getType()) ==
TLI.getPointerTy()) {
if (FindMaximalLegalAddressingMode(AddrInst->getOperand(0), AccessTy,
AddrMode, AddrModeInsts, TLI, Depth))
return true;
}
break;
case Instruction::Add: {
// Check to see if we can merge in the RHS then the LHS. If so, we win.
ExtAddrMode BackupAddrMode = AddrMode;
unsigned OldSize = AddrModeInsts.size();
if (FindMaximalLegalAddressingMode(AddrInst->getOperand(1), AccessTy,
AddrMode, AddrModeInsts, TLI, Depth+1) &&
FindMaximalLegalAddressingMode(AddrInst->getOperand(0), AccessTy,
AddrMode, AddrModeInsts, TLI, Depth+1))
return true;
// Restore the old addr mode info.
AddrMode = BackupAddrMode;
AddrModeInsts.resize(OldSize);
// Otherwise this was over-aggressive. Try merging in the LHS then the RHS.
if (FindMaximalLegalAddressingMode(AddrInst->getOperand(0), AccessTy,
AddrMode, AddrModeInsts, TLI, Depth+1) &&
FindMaximalLegalAddressingMode(AddrInst->getOperand(1), AccessTy,
AddrMode, AddrModeInsts, TLI, Depth+1))
return true;
// Otherwise we definitely can't merge the ADD in.
AddrMode = BackupAddrMode;
AddrModeInsts.resize(OldSize);
break;
}
case Instruction::Or: {
ConstantInt *RHS = dyn_cast<ConstantInt>(AddrInst->getOperand(1));
if (!RHS) break;
// TODO: We can handle "Or Val, Imm" iff this OR is equivalent to an ADD.
break;
}
case Instruction::Mul:
case Instruction::Shl: {
// Can only handle X*C and X << C, and can only handle this when the scale
// field is available.
ConstantInt *RHS = dyn_cast<ConstantInt>(AddrInst->getOperand(1));
if (!RHS) break;
int64_t Scale = RHS->getSExtValue();
if (Opcode == Instruction::Shl)
Scale = 1 << Scale;
if (TryMatchingScaledValue(AddrInst->getOperand(0), Scale, AccessTy,
AddrMode, AddrModeInsts, TLI, Depth))
return true;
break;
}
case Instruction::GetElementPtr: {
// Scan the GEP. We check it if it contains constant offsets and at most
// one variable offset.
int VariableOperand = -1;
unsigned VariableScale = 0;
int64_t ConstantOffset = 0;
const TargetData *TD = TLI.getTargetData();
gep_type_iterator GTI = gep_type_begin(AddrInst);
for (unsigned i = 1, e = AddrInst->getNumOperands(); i != e; ++i, ++GTI) {
if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
const StructLayout *SL = TD->getStructLayout(STy);
unsigned Idx =
cast<ConstantInt>(AddrInst->getOperand(i))->getZExtValue();
ConstantOffset += SL->getElementOffset(Idx);
} else {
uint64_t TypeSize = TD->getTypeSize(GTI.getIndexedType());
if (ConstantInt *CI = dyn_cast<ConstantInt>(AddrInst->getOperand(i))) {
ConstantOffset += CI->getSExtValue()*TypeSize;
} else if (TypeSize) { // Scales of zero don't do anything.
// We only allow one variable index at the moment.
if (VariableOperand != -1) {
VariableOperand = -2;
break;
}
// Remember the variable index.
VariableOperand = i;
VariableScale = TypeSize;
}
}
}
// If the GEP had multiple variable indices, punt.
if (VariableOperand == -2)
break;
// A common case is for the GEP to only do a constant offset. In this case,
// just add it to the disp field and check validity.
if (VariableOperand == -1) {
AddrMode.BaseOffs += ConstantOffset;
if (ConstantOffset == 0 || TLI.isLegalAddressingMode(AddrMode, AccessTy)){
// Check to see if we can fold the base pointer in too.
if (FindMaximalLegalAddressingMode(AddrInst->getOperand(0), AccessTy,
AddrMode, AddrModeInsts, TLI,
Depth+1))
return true;
}
AddrMode.BaseOffs -= ConstantOffset;
} else {
// Check that this has no base reg yet. If so, we won't have a place to
// put the base of the GEP (assuming it is not a null ptr).
bool SetBaseReg = false;
if (AddrMode.HasBaseReg) {
if (!isa<ConstantPointerNull>(AddrInst->getOperand(0)))
break;
} else {
AddrMode.HasBaseReg = true;
AddrMode.BaseReg = AddrInst->getOperand(0);
SetBaseReg = true;
}
// See if the scale amount is valid for this target.
AddrMode.BaseOffs += ConstantOffset;
if (TryMatchingScaledValue(AddrInst->getOperand(VariableOperand),
VariableScale, AccessTy, AddrMode,
AddrModeInsts, TLI, Depth)) {
if (!SetBaseReg) return true;
// If this match succeeded, we know that we can form an address with the
// GepBase as the basereg. See if we can match *more*.
AddrMode.HasBaseReg = false;
AddrMode.BaseReg = 0;
if (FindMaximalLegalAddressingMode(AddrInst->getOperand(0), AccessTy,
AddrMode, AddrModeInsts, TLI,
Depth+1))
return true;
// Strange, shouldn't happen. Restore the base reg and succeed the easy
// way.
AddrMode.HasBaseReg = true;
AddrMode.BaseReg = AddrInst->getOperand(0);
return true;
}
AddrMode.BaseOffs -= ConstantOffset;
if (SetBaseReg) {
AddrMode.HasBaseReg = false;
AddrMode.BaseReg = 0;
}
}
break;
}
}
if (Instruction *I = dyn_cast_or_null<Instruction>(AddrInst)) {
assert(AddrModeInsts.back() == I && "Stack imbalance");
AddrModeInsts.pop_back();
}
// Worse case, the target should support [reg] addressing modes. :)
if (!AddrMode.HasBaseReg) {
AddrMode.HasBaseReg = true;
// Still check for legality in case the target supports [imm] but not [i+r].
if (TLI.isLegalAddressingMode(AddrMode, AccessTy)) {
AddrMode.BaseReg = Addr;
return true;
}
AddrMode.HasBaseReg = false;
}
// If the base register is already taken, see if we can do [r+r].
if (AddrMode.Scale == 0) {
AddrMode.Scale = 1;
if (TLI.isLegalAddressingMode(AddrMode, AccessTy)) {
AddrMode.ScaledReg = Addr;
return true;
}
AddrMode.Scale = 0;
}
// Couldn't match.
return false;
}
/// TryMatchingScaledValue - Try adding ScaleReg*Scale to the specified
/// addressing mode. Return true if this addr mode is legal for the target,
/// false if not.
static bool TryMatchingScaledValue(Value *ScaleReg, int64_t Scale,
const Type *AccessTy, ExtAddrMode &AddrMode,
SmallVector<Instruction*, 16> &AddrModeInsts,
const TargetLowering &TLI, unsigned Depth) {
// If we already have a scale of this value, we can add to it, otherwise, we
// need an available scale field.
if (AddrMode.Scale != 0 && AddrMode.ScaledReg != ScaleReg)
return false;
ExtAddrMode InputAddrMode = AddrMode;
// Add scale to turn X*4+X*3 -> X*7. This could also do things like
// [A+B + A*7] -> [B+A*8].
AddrMode.Scale += Scale;
AddrMode.ScaledReg = ScaleReg;
if (TLI.isLegalAddressingMode(AddrMode, AccessTy)) {
// Okay, we decided that we can add ScaleReg+Scale to AddrMode. Check now
// to see if ScaleReg is actually X+C. If so, we can turn this into adding
// X*Scale + C*Scale to addr mode.
BinaryOperator *BinOp = dyn_cast<BinaryOperator>(ScaleReg);
if (BinOp && BinOp->getOpcode() == Instruction::Add &&
isa<ConstantInt>(BinOp->getOperand(1)) && InputAddrMode.ScaledReg ==0) {
InputAddrMode.Scale = Scale;
InputAddrMode.ScaledReg = BinOp->getOperand(0);
InputAddrMode.BaseOffs +=
cast<ConstantInt>(BinOp->getOperand(1))->getSExtValue()*Scale;
if (TLI.isLegalAddressingMode(InputAddrMode, AccessTy)) {
AddrModeInsts.push_back(BinOp);
AddrMode = InputAddrMode;
return true;
}
}
// Otherwise, not (x+c)*scale, just return what we have.
return true;
}
// Otherwise, back this attempt out.
AddrMode.Scale -= Scale;
if (AddrMode.Scale == 0) AddrMode.ScaledReg = 0;
return false;
}
/// IsNonLocalValue - Return true if the specified values are defined in a
/// different basic block than BB.
static bool IsNonLocalValue(Value *V, BasicBlock *BB) {
if (Instruction *I = dyn_cast<Instruction>(V))
return I->getParent() != BB;
return false;
}
/// OptimizeLoadStoreInst - Load and Store Instructions have often have
/// addressing modes that can do significant amounts of computation. As such,
/// instruction selection will try to get the load or store to do as much
/// computation as possible for the program. The problem is that isel can only
/// see within a single block. As such, we sink as much legal addressing mode
/// stuff into the block as possible.
bool CodeGenPrepare::OptimizeLoadStoreInst(Instruction *LdStInst, Value *Addr,
const Type *AccessTy,
DenseMap<Value*,Value*> &SunkAddrs) {
// Figure out what addressing mode will be built up for this operation.
SmallVector<Instruction*, 16> AddrModeInsts;
ExtAddrMode AddrMode;
bool Success = FindMaximalLegalAddressingMode(Addr, AccessTy, AddrMode,
AddrModeInsts, *TLI, 0);
Success = Success; assert(Success && "Couldn't select *anything*?");
// Check to see if any of the instructions supersumed by this addr mode are
// non-local to I's BB.
bool AnyNonLocal = false;
for (unsigned i = 0, e = AddrModeInsts.size(); i != e; ++i) {
if (IsNonLocalValue(AddrModeInsts[i], LdStInst->getParent())) {
AnyNonLocal = true;
break;
}
}
// If all the instructions matched are already in this BB, don't do anything.
if (!AnyNonLocal) {
DEBUG(cerr << "CGP: Found local addrmode: " << AddrMode << "\n");
return false;
}
// Insert this computation right after this user. Since our caller is
// scanning from the top of the BB to the bottom, reuse of the expr are
// guaranteed to happen later.
BasicBlock::iterator InsertPt = LdStInst;
// Now that we determined the addressing expression we want to use and know
// that we have to sink it into this block. Check to see if we have already
// done this for some other load/store instr in this block. If so, reuse the
// computation.
Value *&SunkAddr = SunkAddrs[Addr];
if (SunkAddr) {
DEBUG(cerr << "CGP: Reusing nonlocal addrmode: " << AddrMode << "\n");
if (SunkAddr->getType() != Addr->getType())
SunkAddr = new BitCastInst(SunkAddr, Addr->getType(), "tmp", InsertPt);
} else {
DEBUG(cerr << "CGP: SINKING nonlocal addrmode: " << AddrMode << "\n");
const Type *IntPtrTy = TLI->getTargetData()->getIntPtrType();
Value *Result = 0;
// Start with the scale value.
if (AddrMode.Scale) {
Value *V = AddrMode.ScaledReg;
if (V->getType() == IntPtrTy) {
// done.
} else if (isa<PointerType>(V->getType())) {
V = new PtrToIntInst(V, IntPtrTy, "sunkaddr", InsertPt);
} else if (cast<IntegerType>(IntPtrTy)->getBitWidth() <
cast<IntegerType>(V->getType())->getBitWidth()) {
V = new TruncInst(V, IntPtrTy, "sunkaddr", InsertPt);
} else {
V = new SExtInst(V, IntPtrTy, "sunkaddr", InsertPt);
}
if (AddrMode.Scale != 1)
V = BinaryOperator::createMul(V, ConstantInt::get(IntPtrTy,
AddrMode.Scale),
"sunkaddr", InsertPt);
Result = V;
}
// Add in the base register.
if (AddrMode.BaseReg) {
Value *V = AddrMode.BaseReg;
if (V->getType() != IntPtrTy)
V = new PtrToIntInst(V, IntPtrTy, "sunkaddr", InsertPt);
if (Result)
Result = BinaryOperator::createAdd(Result, V, "sunkaddr", InsertPt);
else
Result = V;
}
// Add in the BaseGV if present.
if (AddrMode.BaseGV) {
Value *V = new PtrToIntInst(AddrMode.BaseGV, IntPtrTy, "sunkaddr",
InsertPt);
if (Result)
Result = BinaryOperator::createAdd(Result, V, "sunkaddr", InsertPt);
else
Result = V;
}
// Add in the Base Offset if present.
if (AddrMode.BaseOffs) {
Value *V = ConstantInt::get(IntPtrTy, AddrMode.BaseOffs);
if (Result)
Result = BinaryOperator::createAdd(Result, V, "sunkaddr", InsertPt);
else
Result = V;
}
if (Result == 0)
SunkAddr = Constant::getNullValue(Addr->getType());
else
SunkAddr = new IntToPtrInst(Result, Addr->getType(), "sunkaddr",InsertPt);
}
LdStInst->replaceUsesOfWith(Addr, SunkAddr);
if (Addr->use_empty())
EraseDeadInstructions(Addr);
return true;
}
// In this pass we look for GEP and cast instructions that are used
// across basic blocks and rewrite them to improve basic-block-at-a-time
// selection.
bool CodeGenPrepare::OptimizeBlock(BasicBlock &BB) {
bool MadeChange = false;
// Split all critical edges where the dest block has a PHI and where the phi
// has shared immediate operands.
TerminatorInst *BBTI = BB.getTerminator();
if (BBTI->getNumSuccessors() > 1) {
for (unsigned i = 0, e = BBTI->getNumSuccessors(); i != e; ++i)
if (isa<PHINode>(BBTI->getSuccessor(i)->begin()) &&
isCriticalEdge(BBTI, i, true))
SplitEdgeNicely(BBTI, i, this);
}
// Keep track of non-local addresses that have been sunk into this block.
// This allows us to avoid inserting duplicate code for blocks with multiple
// load/stores of the same address.
DenseMap<Value*, Value*> SunkAddrs;
for (BasicBlock::iterator BBI = BB.begin(), E = BB.end(); BBI != E; ) {
Instruction *I = BBI++;
if (CastInst *CI = dyn_cast<CastInst>(I)) {
// If the source of the cast is a constant, then this should have
// already been constant folded. The only reason NOT to constant fold
// it is if something (e.g. LSR) was careful to place the constant
// evaluation in a block other than then one that uses it (e.g. to hoist
// the address of globals out of a loop). If this is the case, we don't
// want to forward-subst the cast.
if (isa<Constant>(CI->getOperand(0)))
continue;
if (TLI)
MadeChange |= OptimizeNoopCopyExpression(CI, *TLI);
} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
if (TLI)
MadeChange |= OptimizeLoadStoreInst(I, I->getOperand(0), LI->getType(),
SunkAddrs);
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
if (TLI)
MadeChange |= OptimizeLoadStoreInst(I, SI->getOperand(1),
SI->getOperand(0)->getType(),
SunkAddrs);
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
if (GEPI->hasAllZeroIndices()) {
/// The GEP operand must be a pointer, so must its result -> BitCast
Instruction *NC = new BitCastInst(GEPI->getOperand(0), GEPI->getType(),
GEPI->getName(), GEPI);
GEPI->replaceAllUsesWith(NC);
GEPI->eraseFromParent();
MadeChange = true;
BBI = NC;
}
} else if (CallInst *CI = dyn_cast<CallInst>(I)) {
// If we found an inline asm expession, and if the target knows how to
// lower it to normal LLVM code, do so now.
if (TLI && isa<InlineAsm>(CI->getCalledValue()))
if (const TargetAsmInfo *TAI =
TLI->getTargetMachine().getTargetAsmInfo()) {
if (TAI->ExpandInlineAsm(CI))
BBI = BB.begin();
}
}
}
return MadeChange;
}