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a40df277f1
llvm-mirror/lib/Transforms/Scalar/CodeGenPrepare.cpp
Cameron Zwarich a40df277f1 Make more passes preserve dominators (or state that they preserve dominators if 
they all ready do). This removes two dominator recomputations prior to isel,
which is a 1% improvement in total llc time for 403.gcc.

The only potentially suspect thing is making GCStrategy recompute dominators if
it used a custom lowering strategy.

llvm-svn: 123064
2011-01-08 17:01:52 +00:00

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//===- CodeGenPrepare.cpp - Prepare a function for code generation --------===//
//
// The LLVM Compiler Infrastructure
//
// This file 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/InlineAsm.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ProfileInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Transforms/Utils/AddrModeMatcher.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BuildLibCalls.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/IRBuilder.h"
using namespace llvm;
using namespace llvm::PatternMatch;
STATISTIC(NumBlocksElim, "Number of blocks eliminated");
STATISTIC(NumPHIsElim, "Number of trivial PHIs eliminated");
STATISTIC(NumGEPsElim, "Number of GEPs converted to casts");
STATISTIC(NumCmpUses, "Number of uses of Cmp expressions replaced with uses of "
"sunken Cmps");
STATISTIC(NumCastUses, "Number of uses of Cast expressions replaced with uses "
"of sunken Casts");
STATISTIC(NumMemoryInsts, "Number of memory instructions whose address "
"computations were sunk");
STATISTIC(NumExtsMoved, "Number of [s|z]ext instructions combined with loads");
STATISTIC(NumExtUses, "Number of uses of [s|z]ext instructions optimized");
static cl::opt<bool>
CriticalEdgeSplit("cgp-critical-edge-splitting",
cl::desc("Split critical edges during codegen prepare"),
cl::init(false), cl::Hidden);
namespace {
class CodeGenPrepare : public FunctionPass {
/// TLI - Keep a pointer of a TargetLowering to consult for determining
/// transformation profitability.
const TargetLowering *TLI;
DominatorTree *DT;
ProfileInfo *PFI;
/// BackEdges - Keep a set of all the loop back edges.
///
SmallSet<std::pair<const BasicBlock*, const BasicBlock*>, 8> BackEdges;
// Keeps track of non-local addresses that have been sunk into a block. This
// allows us to avoid inserting duplicate code for blocks with multiple
// load/stores of the same address.
DenseMap<Value*, Value*> SunkAddrs;
public:
static char ID; // Pass identification, replacement for typeid
explicit CodeGenPrepare(const TargetLowering *tli = 0)
: FunctionPass(ID), TLI(tli) {
initializeCodeGenPreparePass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addPreserved<DominatorTree>();
AU.addPreserved<ProfileInfo>();
}
virtual void releaseMemory() {
BackEdges.clear();
}
private:
bool EliminateMostlyEmptyBlocks(Function &F);
bool CanMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const;
void EliminateMostlyEmptyBlock(BasicBlock *BB);
bool OptimizeBlock(BasicBlock &BB);
bool OptimizeInst(Instruction *I);
bool OptimizeMemoryInst(Instruction *I, Value *Addr, const Type *AccessTy,
DenseMap<Value*,Value*> &SunkAddrs);
bool OptimizeInlineAsmInst(Instruction *I, CallSite CS,
DenseMap<Value*,Value*> &SunkAddrs);
bool OptimizeCallInst(CallInst *CI);
bool MoveExtToFormExtLoad(Instruction *I);
bool OptimizeExtUses(Instruction *I);
void findLoopBackEdges(const Function &F);
};
}
char CodeGenPrepare::ID = 0;
INITIALIZE_PASS(CodeGenPrepare, "codegenprepare",
"Optimize for code generation", false, false)
FunctionPass *llvm::createCodeGenPreparePass(const TargetLowering *TLI) {
return new CodeGenPrepare(TLI);
}
/// findLoopBackEdges - Do a DFS walk to find loop back edges.
///
void CodeGenPrepare::findLoopBackEdges(const Function &F) {
SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
FindFunctionBackedges(F, Edges);
BackEdges.insert(Edges.begin(), Edges.end());
}
bool CodeGenPrepare::runOnFunction(Function &F) {
bool EverMadeChange = false;
DT = getAnalysisIfAvailable<DominatorTree>();
PFI = getAnalysisIfAvailable<ProfileInfo>();
// First pass, eliminate blocks that contain only PHI nodes and an
// unconditional branch.
EverMadeChange |= EliminateMostlyEmptyBlocks(F);
// Now find loop back edges, but only if they are being used to decide which
// critical edges to split.
if (CriticalEdgeSplit)
findLoopBackEdges(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;
}
SunkAddrs.clear();
return EverMadeChange;
}
/// EliminateMostlyEmptyBlocks - eliminate blocks that contain only PHI nodes,
/// debug info directives, 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 (skipping debug info) isn't a phi
// node, then other stuff is happening here.
BasicBlock::iterator BBI = BI;
if (BBI != BB->begin()) {
--BBI;
while (isa<DbgInfoIntrinsic>(BBI)) {
if (BBI == BB->begin())
break;
--BBI;
}
if (!isa<DbgInfoIntrinsic>(BBI) && !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::const_use_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<const 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);
DEBUG(dbgs() << "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 (BasicBlock *SinglePred = DestBB->getSinglePredecessor()) {
if (SinglePred != DestBB) {
// Remember if SinglePred was the entry block of the function. If so, we
// will need to move BB back to the entry position.
bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
MergeBasicBlockIntoOnlyPred(DestBB, this);
if (isEntry && BB != &BB->getParent()->getEntryBlock())
BB->moveBefore(&BB->getParent()->getEntryBlock());
DEBUG(dbgs() << "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);
if (DT) {
BasicBlock *BBIDom = DT->getNode(BB)->getIDom()->getBlock();
BasicBlock *DestBBIDom = DT->getNode(DestBB)->getIDom()->getBlock();
BasicBlock *NewIDom = DT->findNearestCommonDominator(BBIDom, DestBBIDom);
DT->changeImmediateDominator(DestBB, NewIDom);
DT->eraseNode(BB);
}
if (PFI) {
PFI->replaceAllUses(BB, DestBB);
PFI->removeEdge(ProfileInfo::getEdge(BB, DestBB));
}
BB->eraseFromParent();
++NumBlocksElim;
DEBUG(dbgs() << "AFTER:\n" << *DestBB << "\n\n\n");
}
/// FindReusablePredBB - Check all of the predecessors of the block DestPHI
/// lives in to see if there is a block that we can reuse as a critical edge
/// from TIBB.
static BasicBlock *FindReusablePredBB(PHINode *DestPHI, BasicBlock *TIBB) {
BasicBlock *Dest = DestPHI->getParent();
/// TIPHIValues - This array is lazily computed to determine the values of
/// PHIs in Dest that TI would provide.
SmallVector<Value*, 32> TIPHIValues;
/// TIBBEntryNo - This is a cache to speed up pred queries for TIBB.
unsigned TIBBEntryNo = 0;
// Check to see if Dest has any blocks that can be used as a split edge for
// this terminator.
for (unsigned pi = 0, e = DestPHI->getNumIncomingValues(); pi != e; ++pi) {
BasicBlock *Pred = DestPHI->getIncomingBlock(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())
continue;
// Must be empty other than the branch and debug info.
BasicBlock::iterator I = Pred->begin();
while (isa<DbgInfoIntrinsic>(I))
I++;
if (&*I != PredBr)
continue;
// Cannot be the entry block; its label does not get emitted.
if (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 effect as going to Dest in
// terms of PHI values.
PHINode *PN;
unsigned PHINo = 0;
unsigned PredEntryNo = pi;
bool FoundMatch = true;
for (BasicBlock::iterator I = Dest->begin();
(PN = dyn_cast<PHINode>(I)); ++I, ++PHINo) {
if (PHINo == TIPHIValues.size()) {
if (PN->getIncomingBlock(TIBBEntryNo) != TIBB)
TIBBEntryNo = PN->getBasicBlockIndex(TIBB);
TIPHIValues.push_back(PN->getIncomingValue(TIBBEntryNo));
}
// If the PHI entry doesn't work, we can't use this pred.
if (PN->getIncomingBlock(PredEntryNo) != Pred)
PredEntryNo = PN->getBasicBlockIndex(Pred);
if (TIPHIValues[PHINo] != PN->getIncomingValue(PredEntryNo)) {
FoundMatch = false;
break;
}
}
// If we found a workable predecessor, change TI to branch to Succ.
if (FoundMatch)
return Pred;
}
return 0;
}
/// SplitEdgeNicely - Split the critical edge from TI to its 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,
SmallSet<std::pair<const BasicBlock*,
const BasicBlock*>, 8> &BackEdges,
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!");
PHINode *DestPHI = cast<PHINode>(Dest->begin());
// Do not split edges to EH landing pads.
if (InvokeInst *Invoke = dyn_cast<InvokeInst>(TI))
if (Invoke->getSuccessor(1) == Dest)
return;
// As a hack, never split backedges of loops. Even though the copy for any
// PHIs inserted on the backedge would be dead for exits from the loop, we
// assume that the cost of *splitting* the backedge would be too high.
if (BackEdges.count(std::make_pair(TIBB, Dest)))
return;
if (BasicBlock *ReuseBB = FindReusablePredBB(DestPHI, TIBB)) {
ProfileInfo *PFI = P->getAnalysisIfAvailable<ProfileInfo>();
if (PFI)
PFI->splitEdge(TIBB, Dest, ReuseBB);
Dest->removePredecessor(TIBB);
TI->setSuccessor(SuccNum, ReuseBB);
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, i32->i8 on PPC),
/// sink it into user blocks to reduce the number of virtual
/// registers that must be created and coalesced.
///
/// Return true if any changes are made.
///
static bool OptimizeNoopCopyExpression(CastInst *CI, const TargetLowering &TLI){
// If this is a noop copy,
EVT SrcVT = TLI.getValueType(CI->getOperand(0)->getType());
EVT DstVT = TLI.getValueType(CI->getType());
// This is an fp<->int conversion?
if (SrcVT.isInteger() != DstVT.isInteger())
return false;
// If this is an extension, it will be a zero or sign extension, which
// isn't a noop.
if (SrcVT.bitsLT(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(CI->getContext(), SrcVT);
if (TLI.getTypeAction(DstVT) == TargetLowering::Promote)
DstVT = TLI.getTypeToTransformTo(CI->getContext(), 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.
DenseMap<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)) {
UserBB = PN->getIncomingBlock(UI);
}
// 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->getFirstNonPHI();
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 cast.
TheUse = InsertedCast;
++NumCastUses;
}
// If we removed all uses, nuke the cast.
if (CI->use_empty()) {
CI->eraseFromParent();
MadeChange = true;
}
return MadeChange;
}
/// OptimizeCmpExpression - sink the given CmpInst into user blocks to reduce
/// the number of virtual registers that must be created and coalesced. This is
/// a clear win except on targets with multiple condition code registers
/// (PowerPC), where it might lose; some adjustment may be wanted there.
///
/// Return true if any changes are made.
static bool OptimizeCmpExpression(CmpInst *CI) {
BasicBlock *DefBB = CI->getParent();
/// InsertedCmp - Only insert a cmp in each block once.
DenseMap<BasicBlock*, CmpInst*> InsertedCmps;
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);
// Preincrement use iterator so we don't invalidate it.
++UI;
// Don't bother for PHI nodes.
if (isa<PHINode>(User))
continue;
// Figure out which BB this cmp is used in.
BasicBlock *UserBB = User->getParent();
// If this user is in the same block as the cmp, don't change the cmp.
if (UserBB == DefBB) continue;
// If we have already inserted a cmp into this block, use it.
CmpInst *&InsertedCmp = InsertedCmps[UserBB];
if (!InsertedCmp) {
BasicBlock::iterator InsertPt = UserBB->getFirstNonPHI();
InsertedCmp =
CmpInst::Create(CI->getOpcode(),
CI->getPredicate(), CI->getOperand(0),
CI->getOperand(1), "", InsertPt);
MadeChange = true;
}
// Replace a use of the cmp with a use of the new cmp.
TheUse = InsertedCmp;
++NumCmpUses;
}
// If we removed all uses, nuke the cmp.
if (CI->use_empty())
CI->eraseFromParent();
return MadeChange;
}
namespace {
class CodeGenPrepareFortifiedLibCalls : public SimplifyFortifiedLibCalls {
protected:
void replaceCall(Value *With) {
CI->replaceAllUsesWith(With);
CI->eraseFromParent();
}
bool isFoldable(unsigned SizeCIOp, unsigned, bool) const {
if (ConstantInt *SizeCI =
dyn_cast<ConstantInt>(CI->getArgOperand(SizeCIOp)))
return SizeCI->isAllOnesValue();
return false;
}
};
} // end anonymous namespace
bool CodeGenPrepare::OptimizeCallInst(CallInst *CI) {
// Lower all uses of llvm.objectsize.*
IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI);
if (II && II->getIntrinsicID() == Intrinsic::objectsize) {
bool Min = (cast<ConstantInt>(II->getArgOperand(1))->getZExtValue() == 1);
const Type *ReturnTy = CI->getType();
Constant *RetVal = ConstantInt::get(ReturnTy, Min ? 0 : -1ULL);
CI->replaceAllUsesWith(RetVal);
CI->eraseFromParent();
return true;
}
// From here on out we're working with named functions.
if (CI->getCalledFunction() == 0) return false;
// We'll need TargetData from here on out.
const TargetData *TD = TLI ? TLI->getTargetData() : 0;
if (!TD) return false;
// Lower all default uses of _chk calls. This is very similar
// to what InstCombineCalls does, but here we are only lowering calls
// that have the default "don't know" as the objectsize. Anything else
// should be left alone.
CodeGenPrepareFortifiedLibCalls Simplifier;
return Simplifier.fold(CI, TD);
}
//===----------------------------------------------------------------------===//
// Memory Optimization
//===----------------------------------------------------------------------===//
/// 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;
}
/// OptimizeMemoryInst - Load and Store Instructions 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.
///
/// This method is used to optimize both load/store and inline asms with memory
/// operands.
bool CodeGenPrepare::OptimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
const Type *AccessTy,
DenseMap<Value*,Value*> &SunkAddrs) {
Value *Repl = Addr;
// Try to collapse single-value PHI nodes. This is necessary to undo
// unprofitable PRE transformations.
SmallVector<Value*, 8> worklist;
SmallPtrSet<Value*, 16> Visited;
worklist.push_back(Addr);
// Use a worklist to iteratively look through PHI nodes, and ensure that
// the addressing mode obtained from the non-PHI roots of the graph
// are equivalent.
Value *Consensus = 0;
unsigned NumUses = 0;
SmallVector<Instruction*, 16> AddrModeInsts;
ExtAddrMode AddrMode;
while (!worklist.empty()) {
Value *V = worklist.back();
worklist.pop_back();
// Break use-def graph loops.
if (Visited.count(V)) {
Consensus = 0;
break;
}
Visited.insert(V);
// For a PHI node, push all of its incoming values.
if (PHINode *P = dyn_cast<PHINode>(V)) {
for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i)
worklist.push_back(P->getIncomingValue(i));
continue;
}
// For non-PHIs, determine the addressing mode being computed.
SmallVector<Instruction*, 16> NewAddrModeInsts;
ExtAddrMode NewAddrMode =
AddressingModeMatcher::Match(V, AccessTy,MemoryInst,
NewAddrModeInsts, *TLI);
// Ensure that the obtained addressing mode is equivalent to that obtained
// for all other roots of the PHI traversal. Also, when choosing one
// such root as representative, select the one with the most uses in order
// to keep the cost modeling heuristics in AddressingModeMatcher applicable.
if (!Consensus || NewAddrMode == AddrMode) {
if (V->getNumUses() > NumUses) {
Consensus = V;
NumUses = V->getNumUses();
AddrMode = NewAddrMode;
AddrModeInsts = NewAddrModeInsts;
}
continue;
}
Consensus = 0;
break;
}
// If the addressing mode couldn't be determined, or if multiple different
// ones were determined, bail out now.
if (!Consensus) return false;
// 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], MemoryInst->getParent())) {
AnyNonLocal = true;
break;
}
}
// If all the instructions matched are already in this BB, don't do anything.
if (!AnyNonLocal) {
DEBUG(dbgs() << "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 = MemoryInst;
// 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(dbgs() << "CGP: Reusing nonlocal addrmode: " << AddrMode << " for "
<< *MemoryInst);
if (SunkAddr->getType() != Addr->getType())
SunkAddr = new BitCastInst(SunkAddr, Addr->getType(), "tmp", InsertPt);
} else {
DEBUG(dbgs() << "CGP: SINKING nonlocal addrmode: " << AddrMode << " for "
<< *MemoryInst);
const Type *IntPtrTy =
TLI->getTargetData()->getIntPtrType(AccessTy->getContext());
Value *Result = 0;
// Start with the base register. Do this first so that subsequent address
// matching finds it last, which will prevent it from trying to match it
// as the scaled value in case it happens to be a mul. That would be
// problematic if we've sunk a different mul for the scale, because then
// we'd end up sinking both muls.
if (AddrMode.BaseReg) {
Value *V = AddrMode.BaseReg;
if (V->getType()->isPointerTy())
V = new PtrToIntInst(V, IntPtrTy, "sunkaddr", InsertPt);
if (V->getType() != IntPtrTy)
V = CastInst::CreateIntegerCast(V, IntPtrTy, /*isSigned=*/true,
"sunkaddr", InsertPt);
Result = V;
}
// Add the scale value.
if (AddrMode.Scale) {
Value *V = AddrMode.ScaledReg;
if (V->getType() == IntPtrTy) {
// done.
} else if (V->getType()->isPointerTy()) {
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);
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);
}
MemoryInst->replaceUsesOfWith(Repl, SunkAddr);
if (Repl->use_empty()) {
RecursivelyDeleteTriviallyDeadInstructions(Repl);
// This address is now available for reassignment, so erase the table entry;
// we don't want to match some completely different instruction.
SunkAddrs[Addr] = 0;
}
++NumMemoryInsts;
return true;
}
/// OptimizeInlineAsmInst - If there are any memory operands, use
/// OptimizeMemoryInst to sink their address computing into the block when
/// possible / profitable.
bool CodeGenPrepare::OptimizeInlineAsmInst(Instruction *I, CallSite CS,
DenseMap<Value*,Value*> &SunkAddrs) {
bool MadeChange = false;
TargetLowering::AsmOperandInfoVector TargetConstraints = TLI->ParseConstraints(CS);
unsigned ArgNo = 0;
for (unsigned i = 0, e = TargetConstraints.size(); i != e; ++i) {
TargetLowering::AsmOperandInfo &OpInfo = TargetConstraints[i];
// Compute the constraint code and ConstraintType to use.
TLI->ComputeConstraintToUse(OpInfo, SDValue());
if (OpInfo.ConstraintType == TargetLowering::C_Memory &&
OpInfo.isIndirect) {
Value *OpVal = const_cast<Value *>(CS.getArgument(ArgNo++));
MadeChange |= OptimizeMemoryInst(I, OpVal, OpVal->getType(), SunkAddrs);
} else if (OpInfo.Type == InlineAsm::isInput)
ArgNo++;
}
return MadeChange;
}
/// MoveExtToFormExtLoad - Move a zext or sext fed by a load into the same
/// basic block as the load, unless conditions are unfavorable. This allows
/// SelectionDAG to fold the extend into the load.
///
bool CodeGenPrepare::MoveExtToFormExtLoad(Instruction *I) {
// Look for a load being extended.
LoadInst *LI = dyn_cast<LoadInst>(I->getOperand(0));
if (!LI) return false;
// If they're already in the same block, there's nothing to do.
if (LI->getParent() == I->getParent())
return false;
// If the load has other users and the truncate is not free, this probably
// isn't worthwhile.
if (!LI->hasOneUse() &&
TLI && (TLI->isTypeLegal(TLI->getValueType(LI->getType())) ||
!TLI->isTypeLegal(TLI->getValueType(I->getType()))) &&
!TLI->isTruncateFree(I->getType(), LI->getType()))
return false;
// Check whether the target supports casts folded into loads.
unsigned LType;
if (isa<ZExtInst>(I))
LType = ISD::ZEXTLOAD;
else {
assert(isa<SExtInst>(I) && "Unexpected ext type!");
LType = ISD::SEXTLOAD;
}
if (TLI && !TLI->isLoadExtLegal(LType, TLI->getValueType(LI->getType())))
return false;
// Move the extend into the same block as the load, so that SelectionDAG
// can fold it.
I->removeFromParent();
I->insertAfter(LI);
++NumExtsMoved;
return true;
}
bool CodeGenPrepare::OptimizeExtUses(Instruction *I) {
BasicBlock *DefBB = I->getParent();
// If the result of a {s|z}ext and its source are both live out, rewrite all
// other uses of the source with result of extension.
Value *Src = I->getOperand(0);
if (Src->hasOneUse())
return false;
// Only do this xform if truncating is free.
if (TLI && !TLI->isTruncateFree(I->getType(), Src->getType()))
return false;
// Only safe to perform the optimization if the source is also defined in
// this block.
if (!isa<Instruction>(Src) || DefBB != cast<Instruction>(Src)->getParent())
return false;
bool DefIsLiveOut = false;
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
UI != E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
// Figure out which BB this ext is used in.
BasicBlock *UserBB = User->getParent();
if (UserBB == DefBB) continue;
DefIsLiveOut = true;
break;
}
if (!DefIsLiveOut)
return false;
// Make sure non of the uses are PHI nodes.
for (Value::use_iterator UI = Src->use_begin(), E = Src->use_end();
UI != E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
BasicBlock *UserBB = User->getParent();
if (UserBB == DefBB) continue;
// Be conservative. We don't want this xform to end up introducing
// reloads just before load / store instructions.
if (isa<PHINode>(User) || isa<LoadInst>(User) || isa<StoreInst>(User))
return false;
}
// InsertedTruncs - Only insert one trunc in each block once.
DenseMap<BasicBlock*, Instruction*> InsertedTruncs;
bool MadeChange = false;
for (Value::use_iterator UI = Src->use_begin(), E = Src->use_end();
UI != E; ++UI) {
Use &TheUse = UI.getUse();
Instruction *User = cast<Instruction>(*UI);
// Figure out which BB this ext is used in.
BasicBlock *UserBB = User->getParent();
if (UserBB == DefBB) continue;
// Both src and def are live in this block. Rewrite the use.
Instruction *&InsertedTrunc = InsertedTruncs[UserBB];
if (!InsertedTrunc) {
BasicBlock::iterator InsertPt = UserBB->getFirstNonPHI();
InsertedTrunc = new TruncInst(I, Src->getType(), "", InsertPt);
}
// Replace a use of the {s|z}ext source with a use of the result.
TheUse = InsertedTrunc;
++NumExtUses;
MadeChange = true;
}
return MadeChange;
}
bool CodeGenPrepare::OptimizeInst(Instruction *I) {
bool MadeChange = false;
if (PHINode *P = dyn_cast<PHINode>(I)) {
// It is possible for very late stage optimizations (such as SimplifyCFG)
// to introduce PHI nodes too late to be cleaned up. If we detect such a
// trivial PHI, go ahead and zap it here.
if (Value *V = SimplifyInstruction(P)) {
P->replaceAllUsesWith(V);
P->eraseFromParent();
++NumPHIsElim;
}
} else 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)))
return false;
bool Change = false;
if (TLI) {
Change = OptimizeNoopCopyExpression(CI, *TLI);
MadeChange |= Change;
}
if (!Change && (isa<ZExtInst>(I) || isa<SExtInst>(I))) {
MadeChange |= MoveExtToFormExtLoad(I);
MadeChange |= OptimizeExtUses(I);
}
} else if (CmpInst *CI = dyn_cast<CmpInst>(I)) {
MadeChange |= OptimizeCmpExpression(CI);
} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
if (TLI)
MadeChange |= OptimizeMemoryInst(I, I->getOperand(0), LI->getType(),
SunkAddrs);
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
if (TLI)
MadeChange |= OptimizeMemoryInst(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();
++NumGEPsElim;
MadeChange = true;
OptimizeInst(NC);
}
} else if (CallInst *CI = dyn_cast<CallInst>(I)) {
if (TLI && isa<InlineAsm>(CI->getCalledValue())) {
// Sink address computing for memory operands into the block.
MadeChange |= OptimizeInlineAsmInst(I, &(*CI), SunkAddrs);
} else {
MadeChange |= OptimizeCallInst(CI);
}
}
return MadeChange;
}
// 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.
if (CriticalEdgeSplit) {
TerminatorInst *BBTI = BB.getTerminator();
if (BBTI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(BBTI)) {
for (unsigned i = 0, e = BBTI->getNumSuccessors(); i != e; ++i) {
BasicBlock *SuccBB = BBTI->getSuccessor(i);
if (isa<PHINode>(SuccBB->begin()) && isCriticalEdge(BBTI, i, true))
SplitEdgeNicely(BBTI, i, BackEdges, this);
}
}
}
SunkAddrs.clear();
for (BasicBlock::iterator BBI = BB.begin(), E = BB.end(); BBI != E; ) {
Instruction *I = BBI++;
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 (TLI->ExpandInlineAsm(CI)) {
BBI = BB.begin();
// Avoid processing instructions out of order, which could cause
// reuse before a value is defined.
SunkAddrs.clear();
} else
// Sink address computing for memory operands into the block.
MadeChange |= OptimizeInlineAsmInst(I, &(*CI), SunkAddrs);
} else {
// Other CallInst optimizations that don't need to muck with the
// enclosing iterator here.
MadeChange |= OptimizeCallInst(CI);
}
} else {
MadeChange |= OptimizeInst(I);
}
}
return MadeChange;
}
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