mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-21 03:29:40 +00:00
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42180 91177308-0d34-0410-b5e6-96231b3b80d8
1204 lines
48 KiB
C++
1204 lines
48 KiB
C++
//===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file was developed by the LLVM research group and is distributed under
|
|
// the University of Illinois Open Source License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This pass transforms loops that contain branches on loop-invariant conditions
|
|
// to have multiple loops. For example, it turns the left into the right code:
|
|
//
|
|
// for (...) if (lic)
|
|
// A for (...)
|
|
// if (lic) A; B; C
|
|
// B else
|
|
// C for (...)
|
|
// A; C
|
|
//
|
|
// This can increase the size of the code exponentially (doubling it every time
|
|
// a loop is unswitched) so we only unswitch if the resultant code will be
|
|
// smaller than a threshold.
|
|
//
|
|
// This pass expects LICM to be run before it to hoist invariant conditions out
|
|
// of the loop, to make the unswitching opportunity obvious.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#define DEBUG_TYPE "loop-unswitch"
|
|
#include "llvm/Transforms/Scalar.h"
|
|
#include "llvm/Constants.h"
|
|
#include "llvm/DerivedTypes.h"
|
|
#include "llvm/Function.h"
|
|
#include "llvm/Instructions.h"
|
|
#include "llvm/Analysis/ConstantFolding.h"
|
|
#include "llvm/Analysis/LoopInfo.h"
|
|
#include "llvm/Analysis/LoopPass.h"
|
|
#include "llvm/Analysis/Dominators.h"
|
|
#include "llvm/Transforms/Utils/Cloning.h"
|
|
#include "llvm/Transforms/Utils/Local.h"
|
|
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/ADT/SmallPtrSet.h"
|
|
#include "llvm/ADT/PostOrderIterator.h"
|
|
#include "llvm/Support/CommandLine.h"
|
|
#include "llvm/Support/Compiler.h"
|
|
#include "llvm/Support/Debug.h"
|
|
#include <algorithm>
|
|
#include <set>
|
|
using namespace llvm;
|
|
|
|
STATISTIC(NumBranches, "Number of branches unswitched");
|
|
STATISTIC(NumSwitches, "Number of switches unswitched");
|
|
STATISTIC(NumSelects , "Number of selects unswitched");
|
|
STATISTIC(NumTrivial , "Number of unswitches that are trivial");
|
|
STATISTIC(NumSimplify, "Number of simplifications of unswitched code");
|
|
|
|
namespace {
|
|
cl::opt<unsigned>
|
|
Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
|
|
cl::init(10), cl::Hidden);
|
|
|
|
class VISIBILITY_HIDDEN LoopUnswitch : public LoopPass {
|
|
LoopInfo *LI; // Loop information
|
|
LPPassManager *LPM;
|
|
|
|
// LoopProcessWorklist - Used to check if second loop needs processing
|
|
// after RewriteLoopBodyWithConditionConstant rewrites first loop.
|
|
std::vector<Loop*> LoopProcessWorklist;
|
|
SmallPtrSet<Value *,8> UnswitchedVals;
|
|
|
|
bool OptimizeForSize;
|
|
bool redoLoop;
|
|
public:
|
|
static char ID; // Pass ID, replacement for typeid
|
|
explicit LoopUnswitch(bool Os = false) :
|
|
LoopPass((intptr_t)&ID), OptimizeForSize(Os), redoLoop(false) {}
|
|
|
|
bool runOnLoop(Loop *L, LPPassManager &LPM);
|
|
bool processLoop(Loop *L);
|
|
|
|
/// This transformation requires natural loop information & requires that
|
|
/// loop preheaders be inserted into the CFG...
|
|
///
|
|
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.addRequiredID(LoopSimplifyID);
|
|
AU.addPreservedID(LoopSimplifyID);
|
|
AU.addRequired<LoopInfo>();
|
|
AU.addPreserved<LoopInfo>();
|
|
AU.addRequiredID(LCSSAID);
|
|
AU.addPreservedID(LCSSAID);
|
|
AU.addPreserved<DominatorTree>();
|
|
AU.addPreserved<DominanceFrontier>();
|
|
}
|
|
|
|
private:
|
|
|
|
/// RemoveLoopFromWorklist - If the specified loop is on the loop worklist,
|
|
/// remove it.
|
|
void RemoveLoopFromWorklist(Loop *L) {
|
|
std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(),
|
|
LoopProcessWorklist.end(), L);
|
|
if (I != LoopProcessWorklist.end())
|
|
LoopProcessWorklist.erase(I);
|
|
}
|
|
|
|
bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L);
|
|
unsigned getLoopUnswitchCost(Loop *L, Value *LIC);
|
|
void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
|
|
BasicBlock *ExitBlock);
|
|
void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
|
|
|
|
void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
|
|
Constant *Val, bool isEqual);
|
|
|
|
void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
|
|
BasicBlock *TrueDest,
|
|
BasicBlock *FalseDest,
|
|
Instruction *InsertPt);
|
|
|
|
void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
|
|
void RemoveBlockIfDead(BasicBlock *BB,
|
|
std::vector<Instruction*> &Worklist, Loop *l);
|
|
void RemoveLoopFromHierarchy(Loop *L);
|
|
};
|
|
char LoopUnswitch::ID = 0;
|
|
RegisterPass<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
|
|
}
|
|
|
|
LoopPass *llvm::createLoopUnswitchPass(bool Os) {
|
|
return new LoopUnswitch(Os);
|
|
}
|
|
|
|
/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
|
|
/// invariant in the loop, or has an invariant piece, return the invariant.
|
|
/// Otherwise, return null.
|
|
static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
|
|
// Constants should be folded, not unswitched on!
|
|
if (isa<Constant>(Cond)) return false;
|
|
|
|
// TODO: Handle: br (VARIANT|INVARIANT).
|
|
// TODO: Hoist simple expressions out of loops.
|
|
if (L->isLoopInvariant(Cond)) return Cond;
|
|
|
|
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
|
|
if (BO->getOpcode() == Instruction::And ||
|
|
BO->getOpcode() == Instruction::Or) {
|
|
// If either the left or right side is invariant, we can unswitch on this,
|
|
// which will cause the branch to go away in one loop and the condition to
|
|
// simplify in the other one.
|
|
if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
|
|
return LHS;
|
|
if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
|
|
return RHS;
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
|
|
LI = &getAnalysis<LoopInfo>();
|
|
LPM = &LPM_Ref;
|
|
bool Changed = false;
|
|
|
|
do {
|
|
redoLoop = false;
|
|
Changed |= processLoop(L);
|
|
} while(redoLoop);
|
|
|
|
return Changed;
|
|
}
|
|
|
|
/// processLoop - Do actual work and unswitch loop if possible and profitable.
|
|
bool LoopUnswitch::processLoop(Loop *L) {
|
|
assert(L->isLCSSAForm());
|
|
bool Changed = false;
|
|
|
|
// Loop over all of the basic blocks in the loop. If we find an interior
|
|
// block that is branching on a loop-invariant condition, we can unswitch this
|
|
// loop.
|
|
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
|
|
I != E; ++I) {
|
|
TerminatorInst *TI = (*I)->getTerminator();
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
|
|
// If this isn't branching on an invariant condition, we can't unswitch
|
|
// it.
|
|
if (BI->isConditional()) {
|
|
// See if this, or some part of it, is loop invariant. If so, we can
|
|
// unswitch on it if we desire.
|
|
Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed);
|
|
if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(),
|
|
L)) {
|
|
++NumBranches;
|
|
return true;
|
|
}
|
|
}
|
|
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
|
|
if (LoopCond && SI->getNumCases() > 1) {
|
|
// Find a value to unswitch on:
|
|
// FIXME: this should chose the most expensive case!
|
|
Constant *UnswitchVal = SI->getCaseValue(1);
|
|
// Do not process same value again and again.
|
|
if (!UnswitchedVals.insert(UnswitchVal))
|
|
continue;
|
|
|
|
if (UnswitchIfProfitable(LoopCond, UnswitchVal, L)) {
|
|
++NumSwitches;
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Scan the instructions to check for unswitchable values.
|
|
for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
|
|
BBI != E; ++BBI)
|
|
if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
|
|
Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
|
|
if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(),
|
|
L)) {
|
|
++NumSelects;
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
|
|
assert(L->isLCSSAForm());
|
|
|
|
return Changed;
|
|
}
|
|
|
|
/// isTrivialLoopExitBlock - Check to see if all paths from BB either:
|
|
/// 1. Exit the loop with no side effects.
|
|
/// 2. Branch to the latch block with no side-effects.
|
|
///
|
|
/// If these conditions are true, we return true and set ExitBB to the block we
|
|
/// exit through.
|
|
///
|
|
static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
|
|
BasicBlock *&ExitBB,
|
|
std::set<BasicBlock*> &Visited) {
|
|
if (!Visited.insert(BB).second) {
|
|
// Already visited and Ok, end of recursion.
|
|
return true;
|
|
} else if (!L->contains(BB)) {
|
|
// Otherwise, this is a loop exit, this is fine so long as this is the
|
|
// first exit.
|
|
if (ExitBB != 0) return false;
|
|
ExitBB = BB;
|
|
return true;
|
|
}
|
|
|
|
// Otherwise, this is an unvisited intra-loop node. Check all successors.
|
|
for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
|
|
// Check to see if the successor is a trivial loop exit.
|
|
if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
|
|
return false;
|
|
}
|
|
|
|
// Okay, everything after this looks good, check to make sure that this block
|
|
// doesn't include any side effects.
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
|
|
if (I->mayWriteToMemory())
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
/// isTrivialLoopExitBlock - Return true if the specified block unconditionally
|
|
/// leads to an exit from the specified loop, and has no side-effects in the
|
|
/// process. If so, return the block that is exited to, otherwise return null.
|
|
static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
|
|
std::set<BasicBlock*> Visited;
|
|
Visited.insert(L->getHeader()); // Branches to header are ok.
|
|
BasicBlock *ExitBB = 0;
|
|
if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
|
|
return ExitBB;
|
|
return 0;
|
|
}
|
|
|
|
/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
|
|
/// trivial: that is, that the condition controls whether or not the loop does
|
|
/// anything at all. If this is a trivial condition, unswitching produces no
|
|
/// code duplications (equivalently, it produces a simpler loop and a new empty
|
|
/// loop, which gets deleted).
|
|
///
|
|
/// If this is a trivial condition, return true, otherwise return false. When
|
|
/// returning true, this sets Cond and Val to the condition that controls the
|
|
/// trivial condition: when Cond dynamically equals Val, the loop is known to
|
|
/// exit. Finally, this sets LoopExit to the BB that the loop exits to when
|
|
/// Cond == Val.
|
|
///
|
|
static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond, Constant **Val = 0,
|
|
BasicBlock **LoopExit = 0) {
|
|
BasicBlock *Header = L->getHeader();
|
|
TerminatorInst *HeaderTerm = Header->getTerminator();
|
|
|
|
BasicBlock *LoopExitBB = 0;
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
|
|
// If the header block doesn't end with a conditional branch on Cond, we
|
|
// can't handle it.
|
|
if (!BI->isConditional() || BI->getCondition() != Cond)
|
|
return false;
|
|
|
|
// Check to see if a successor of the branch is guaranteed to go to the
|
|
// latch block or exit through a one exit block without having any
|
|
// side-effects. If so, determine the value of Cond that causes it to do
|
|
// this.
|
|
if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(0)))) {
|
|
if (Val) *Val = ConstantInt::getTrue();
|
|
} else if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(1)))) {
|
|
if (Val) *Val = ConstantInt::getFalse();
|
|
}
|
|
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
|
|
// If this isn't a switch on Cond, we can't handle it.
|
|
if (SI->getCondition() != Cond) return false;
|
|
|
|
// Check to see if a successor of the switch is guaranteed to go to the
|
|
// latch block or exit through a one exit block without having any
|
|
// side-effects. If so, determine the value of Cond that causes it to do
|
|
// this. Note that we can't trivially unswitch on the default case.
|
|
for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
|
|
if ((LoopExitBB = isTrivialLoopExitBlock(L, SI->getSuccessor(i)))) {
|
|
// Okay, we found a trivial case, remember the value that is trivial.
|
|
if (Val) *Val = SI->getCaseValue(i);
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If we didn't find a single unique LoopExit block, or if the loop exit block
|
|
// contains phi nodes, this isn't trivial.
|
|
if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
|
|
return false; // Can't handle this.
|
|
|
|
if (LoopExit) *LoopExit = LoopExitBB;
|
|
|
|
// We already know that nothing uses any scalar values defined inside of this
|
|
// loop. As such, we just have to check to see if this loop will execute any
|
|
// side-effecting instructions (e.g. stores, calls, volatile loads) in the
|
|
// part of the loop that the code *would* execute. We already checked the
|
|
// tail, check the header now.
|
|
for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
|
|
if (I->mayWriteToMemory())
|
|
return false;
|
|
return true;
|
|
}
|
|
|
|
/// getLoopUnswitchCost - Return the cost (code size growth) that will happen if
|
|
/// we choose to unswitch the specified loop on the specified value.
|
|
///
|
|
unsigned LoopUnswitch::getLoopUnswitchCost(Loop *L, Value *LIC) {
|
|
// If the condition is trivial, always unswitch. There is no code growth for
|
|
// this case.
|
|
if (IsTrivialUnswitchCondition(L, LIC))
|
|
return 0;
|
|
|
|
// FIXME: This is really overly conservative. However, more liberal
|
|
// estimations have thus far resulted in excessive unswitching, which is bad
|
|
// both in compile time and in code size. This should be replaced once
|
|
// someone figures out how a good estimation.
|
|
return L->getBlocks().size();
|
|
|
|
unsigned Cost = 0;
|
|
// FIXME: this is brain dead. It should take into consideration code
|
|
// shrinkage.
|
|
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
|
|
I != E; ++I) {
|
|
BasicBlock *BB = *I;
|
|
// Do not include empty blocks in the cost calculation. This happen due to
|
|
// loop canonicalization and will be removed.
|
|
if (BB->begin() == BasicBlock::iterator(BB->getTerminator()))
|
|
continue;
|
|
|
|
// Count basic blocks.
|
|
++Cost;
|
|
}
|
|
|
|
return Cost;
|
|
}
|
|
|
|
/// UnswitchIfProfitable - We have found that we can unswitch L when
|
|
/// LoopCond == Val to simplify the loop. If we decide that this is profitable,
|
|
/// unswitch the loop, reprocess the pieces, then return true.
|
|
bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){
|
|
// Check to see if it would be profitable to unswitch this loop.
|
|
unsigned Cost = getLoopUnswitchCost(L, LoopCond);
|
|
|
|
// Do not do non-trivial unswitch while optimizing for size.
|
|
if (Cost && OptimizeForSize)
|
|
return false;
|
|
|
|
if (Cost > Threshold) {
|
|
// FIXME: this should estimate growth by the amount of code shared by the
|
|
// resultant unswitched loops.
|
|
//
|
|
DOUT << "NOT unswitching loop %"
|
|
<< L->getHeader()->getName() << ", cost too high: "
|
|
<< L->getBlocks().size() << "\n";
|
|
return false;
|
|
}
|
|
|
|
// If this is a trivial condition to unswitch (which results in no code
|
|
// duplication), do it now.
|
|
Constant *CondVal;
|
|
BasicBlock *ExitBlock;
|
|
if (IsTrivialUnswitchCondition(L, LoopCond, &CondVal, &ExitBlock)) {
|
|
UnswitchTrivialCondition(L, LoopCond, CondVal, ExitBlock);
|
|
} else {
|
|
UnswitchNontrivialCondition(LoopCond, Val, L);
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
// RemapInstruction - Convert the instruction operands from referencing the
|
|
// current values into those specified by ValueMap.
|
|
//
|
|
static inline void RemapInstruction(Instruction *I,
|
|
DenseMap<const Value *, Value*> &ValueMap) {
|
|
for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
|
|
Value *Op = I->getOperand(op);
|
|
DenseMap<const Value *, Value*>::iterator It = ValueMap.find(Op);
|
|
if (It != ValueMap.end()) Op = It->second;
|
|
I->setOperand(op, Op);
|
|
}
|
|
}
|
|
|
|
// CloneDomInfo - NewBB is cloned from Orig basic block. Now clone Dominator
|
|
// Info.
|
|
//
|
|
// If Orig block's immediate dominator is mapped in VM then use corresponding
|
|
// immediate dominator from the map. Otherwise Orig block's dominator is also
|
|
// NewBB's dominator.
|
|
//
|
|
// OrigPreheader is loop pre-header before this pass started
|
|
// updating CFG. NewPrehader is loops new pre-header. However, after CFG
|
|
// manipulation, loop L may not exist. So rely on input parameter NewPreheader.
|
|
void CloneDomInfo(BasicBlock *NewBB, BasicBlock *Orig,
|
|
BasicBlock *NewPreheader, BasicBlock *OrigPreheader,
|
|
BasicBlock *OrigHeader,
|
|
DominatorTree *DT, DominanceFrontier *DF,
|
|
DenseMap<const Value*, Value*> &VM) {
|
|
|
|
// If NewBB alreay has found its place in domiantor tree then no need to do
|
|
// anything.
|
|
if (DT->getNode(NewBB))
|
|
return;
|
|
|
|
// If Orig does not have any immediate domiantor then its clone, NewBB, does
|
|
// not need any immediate dominator.
|
|
DomTreeNode *OrigNode = DT->getNode(Orig);
|
|
if (!OrigNode)
|
|
return;
|
|
DomTreeNode *OrigIDomNode = OrigNode->getIDom();
|
|
if (!OrigIDomNode)
|
|
return;
|
|
|
|
BasicBlock *OrigIDom = NULL;
|
|
|
|
// If Orig is original loop header then its immediate dominator is
|
|
// NewPreheader.
|
|
if (Orig == OrigHeader)
|
|
OrigIDom = NewPreheader;
|
|
|
|
// If Orig is new pre-header then its immediate dominator is
|
|
// original pre-header.
|
|
else if (Orig == NewPreheader)
|
|
OrigIDom = OrigPreheader;
|
|
|
|
// Other as DT to find Orig's immediate dominator.
|
|
else
|
|
OrigIDom = OrigIDomNode->getBlock();
|
|
|
|
// Initially use Orig's immediate dominator as NewBB's immediate dominator.
|
|
BasicBlock *NewIDom = OrigIDom;
|
|
DenseMap<const Value*, Value*>::iterator I = VM.find(OrigIDom);
|
|
if (I != VM.end()) {
|
|
NewIDom = cast<BasicBlock>(I->second);
|
|
|
|
// If NewIDom does not have corresponding dominatore tree node then
|
|
// get one.
|
|
if (!DT->getNode(NewIDom))
|
|
CloneDomInfo(NewIDom, OrigIDom, NewPreheader, OrigPreheader,
|
|
OrigHeader, DT, DF, VM);
|
|
}
|
|
|
|
DT->addNewBlock(NewBB, NewIDom);
|
|
|
|
// Copy cloned dominance frontiner set
|
|
DominanceFrontier::DomSetType NewDFSet;
|
|
if (DF) {
|
|
DominanceFrontier::iterator DFI = DF->find(Orig);
|
|
if ( DFI != DF->end()) {
|
|
DominanceFrontier::DomSetType S = DFI->second;
|
|
for (DominanceFrontier::DomSetType::iterator I = S.begin(), E = S.end();
|
|
I != E; ++I) {
|
|
BasicBlock *BB = *I;
|
|
DenseMap<const Value*, Value*>::iterator IDM = VM.find(BB);
|
|
if (IDM != VM.end())
|
|
NewDFSet.insert(cast<BasicBlock>(IDM->second));
|
|
else
|
|
NewDFSet.insert(BB);
|
|
}
|
|
}
|
|
DF->addBasicBlock(NewBB, NewDFSet);
|
|
}
|
|
}
|
|
|
|
/// CloneLoop - Recursively clone the specified loop and all of its children,
|
|
/// mapping the blocks with the specified map.
|
|
static Loop *CloneLoop(Loop *L, Loop *PL, DenseMap<const Value*, Value*> &VM,
|
|
LoopInfo *LI, LPPassManager *LPM) {
|
|
Loop *New = new Loop();
|
|
|
|
LPM->insertLoop(New, PL);
|
|
|
|
// Add all of the blocks in L to the new loop.
|
|
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
|
|
I != E; ++I)
|
|
if (LI->getLoopFor(*I) == L)
|
|
New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);
|
|
|
|
// Add all of the subloops to the new loop.
|
|
for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
|
|
CloneLoop(*I, New, VM, LI, LPM);
|
|
|
|
return New;
|
|
}
|
|
|
|
/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
|
|
/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
|
|
/// code immediately before InsertPt.
|
|
void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
|
|
BasicBlock *TrueDest,
|
|
BasicBlock *FalseDest,
|
|
Instruction *InsertPt) {
|
|
// Insert a conditional branch on LIC to the two preheaders. The original
|
|
// code is the true version and the new code is the false version.
|
|
Value *BranchVal = LIC;
|
|
if (!isa<ConstantInt>(Val) || Val->getType() != Type::Int1Ty)
|
|
BranchVal = new ICmpInst(ICmpInst::ICMP_EQ, LIC, Val, "tmp", InsertPt);
|
|
else if (Val != ConstantInt::getTrue())
|
|
// We want to enter the new loop when the condition is true.
|
|
std::swap(TrueDest, FalseDest);
|
|
|
|
// Insert the new branch.
|
|
new BranchInst(TrueDest, FalseDest, BranchVal, InsertPt);
|
|
|
|
}
|
|
|
|
|
|
/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
|
|
/// condition in it (a cond branch from its header block to its latch block,
|
|
/// where the path through the loop that doesn't execute its body has no
|
|
/// side-effects), unswitch it. This doesn't involve any code duplication, just
|
|
/// moving the conditional branch outside of the loop and updating loop info.
|
|
void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
|
|
Constant *Val,
|
|
BasicBlock *ExitBlock) {
|
|
DOUT << "loop-unswitch: Trivial-Unswitch loop %"
|
|
<< L->getHeader()->getName() << " [" << L->getBlocks().size()
|
|
<< " blocks] in Function " << L->getHeader()->getParent()->getName()
|
|
<< " on cond: " << *Val << " == " << *Cond << "\n";
|
|
|
|
// First step, split the preheader, so that we know that there is a safe place
|
|
// to insert the conditional branch. We will change 'OrigPH' to have a
|
|
// conditional branch on Cond.
|
|
BasicBlock *OrigPH = L->getLoopPreheader();
|
|
BasicBlock *NewPH = SplitEdge(OrigPH, L->getHeader(), this);
|
|
|
|
// Now that we have a place to insert the conditional branch, create a place
|
|
// to branch to: this is the exit block out of the loop that we should
|
|
// short-circuit to.
|
|
|
|
// Split this block now, so that the loop maintains its exit block, and so
|
|
// that the jump from the preheader can execute the contents of the exit block
|
|
// without actually branching to it (the exit block should be dominated by the
|
|
// loop header, not the preheader).
|
|
assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
|
|
BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
|
|
|
|
// Okay, now we have a position to branch from and a position to branch to,
|
|
// insert the new conditional branch.
|
|
EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
|
|
OrigPH->getTerminator());
|
|
LPM->deleteSimpleAnalysisValue(OrigPH->getTerminator(), L);
|
|
OrigPH->getTerminator()->eraseFromParent();
|
|
|
|
// We need to reprocess this loop, it could be unswitched again.
|
|
redoLoop = true;
|
|
|
|
// Now that we know that the loop is never entered when this condition is a
|
|
// particular value, rewrite the loop with this info. We know that this will
|
|
// at least eliminate the old branch.
|
|
RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
|
|
++NumTrivial;
|
|
}
|
|
|
|
/// VersionLoop - We determined that the loop is profitable to unswitch when LIC
|
|
/// equal Val. Split it into loop versions and test the condition outside of
|
|
/// either loop. Return the loops created as Out1/Out2.
|
|
void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
|
|
Loop *L) {
|
|
Function *F = L->getHeader()->getParent();
|
|
DOUT << "loop-unswitch: Unswitching loop %"
|
|
<< L->getHeader()->getName() << " [" << L->getBlocks().size()
|
|
<< " blocks] in Function " << F->getName()
|
|
<< " when '" << *Val << "' == " << *LIC << "\n";
|
|
|
|
// LoopBlocks contains all of the basic blocks of the loop, including the
|
|
// preheader of the loop, the body of the loop, and the exit blocks of the
|
|
// loop, in that order.
|
|
std::vector<BasicBlock*> LoopBlocks;
|
|
|
|
// First step, split the preheader and exit blocks, and add these blocks to
|
|
// the LoopBlocks list.
|
|
BasicBlock *OrigHeader = L->getHeader();
|
|
BasicBlock *OrigPreheader = L->getLoopPreheader();
|
|
BasicBlock *NewPreheader = SplitEdge(OrigPreheader, L->getHeader(), this);
|
|
LoopBlocks.push_back(NewPreheader);
|
|
|
|
// We want the loop to come after the preheader, but before the exit blocks.
|
|
LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
|
|
|
|
SmallVector<BasicBlock*, 8> ExitBlocks;
|
|
L->getUniqueExitBlocks(ExitBlocks);
|
|
|
|
// Split all of the edges from inside the loop to their exit blocks. Update
|
|
// the appropriate Phi nodes as we do so.
|
|
SmallVector<BasicBlock *,8> MiddleBlocks;
|
|
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
|
|
BasicBlock *ExitBlock = ExitBlocks[i];
|
|
std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock));
|
|
|
|
for (unsigned j = 0, e = Preds.size(); j != e; ++j) {
|
|
BasicBlock* MiddleBlock = SplitEdge(Preds[j], ExitBlock, this);
|
|
MiddleBlocks.push_back(MiddleBlock);
|
|
BasicBlock* StartBlock = Preds[j];
|
|
BasicBlock* EndBlock;
|
|
if (MiddleBlock->getSinglePredecessor() == ExitBlock) {
|
|
EndBlock = MiddleBlock;
|
|
MiddleBlock = EndBlock->getSinglePredecessor();;
|
|
} else {
|
|
EndBlock = ExitBlock;
|
|
}
|
|
|
|
std::set<PHINode*> InsertedPHIs;
|
|
PHINode* OldLCSSA = 0;
|
|
for (BasicBlock::iterator I = EndBlock->begin();
|
|
(OldLCSSA = dyn_cast<PHINode>(I)); ++I) {
|
|
Value* OldValue = OldLCSSA->getIncomingValueForBlock(MiddleBlock);
|
|
PHINode* NewLCSSA = new PHINode(OldLCSSA->getType(),
|
|
OldLCSSA->getName() + ".us-lcssa",
|
|
MiddleBlock->getTerminator());
|
|
NewLCSSA->addIncoming(OldValue, StartBlock);
|
|
OldLCSSA->setIncomingValue(OldLCSSA->getBasicBlockIndex(MiddleBlock),
|
|
NewLCSSA);
|
|
InsertedPHIs.insert(NewLCSSA);
|
|
}
|
|
|
|
BasicBlock::iterator InsertPt = EndBlock->begin();
|
|
while (dyn_cast<PHINode>(InsertPt)) ++InsertPt;
|
|
for (BasicBlock::iterator I = MiddleBlock->begin();
|
|
(OldLCSSA = dyn_cast<PHINode>(I)) && InsertedPHIs.count(OldLCSSA) == 0;
|
|
++I) {
|
|
PHINode *NewLCSSA = new PHINode(OldLCSSA->getType(),
|
|
OldLCSSA->getName() + ".us-lcssa",
|
|
InsertPt);
|
|
OldLCSSA->replaceAllUsesWith(NewLCSSA);
|
|
NewLCSSA->addIncoming(OldLCSSA, MiddleBlock);
|
|
}
|
|
}
|
|
}
|
|
|
|
// The exit blocks may have been changed due to edge splitting, recompute.
|
|
ExitBlocks.clear();
|
|
L->getUniqueExitBlocks(ExitBlocks);
|
|
|
|
// Add exit blocks to the loop blocks.
|
|
LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
|
|
|
|
DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>();
|
|
DominatorTree *DT = getAnalysisToUpdate<DominatorTree>();
|
|
|
|
// Next step, clone all of the basic blocks that make up the loop (including
|
|
// the loop preheader and exit blocks), keeping track of the mapping between
|
|
// the instructions and blocks.
|
|
std::vector<BasicBlock*> NewBlocks;
|
|
NewBlocks.reserve(LoopBlocks.size());
|
|
DenseMap<const Value*, Value*> ValueMap;
|
|
for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
|
|
BasicBlock *New = CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F);
|
|
NewBlocks.push_back(New);
|
|
ValueMap[LoopBlocks[i]] = New; // Keep the BB mapping.
|
|
LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], New, L);
|
|
}
|
|
|
|
// OutSiders are basic block that are dominated by original header and
|
|
// at the same time they are not part of loop.
|
|
SmallPtrSet<BasicBlock *, 8> OutSiders;
|
|
if (DT) {
|
|
DomTreeNode *OrigHeaderNode = DT->getNode(OrigHeader);
|
|
for(std::vector<DomTreeNode*>::iterator DI = OrigHeaderNode->begin(),
|
|
DE = OrigHeaderNode->end(); DI != DE; ++DI) {
|
|
BasicBlock *B = (*DI)->getBlock();
|
|
|
|
DenseMap<const Value*, Value*>::iterator VI = ValueMap.find(B);
|
|
if (VI == ValueMap.end())
|
|
OutSiders.insert(B);
|
|
}
|
|
}
|
|
|
|
// Splice the newly inserted blocks into the function right before the
|
|
// original preheader.
|
|
F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(),
|
|
NewBlocks[0], F->end());
|
|
|
|
// Now we create the new Loop object for the versioned loop.
|
|
Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI, LPM);
|
|
Loop *ParentLoop = L->getParentLoop();
|
|
if (ParentLoop) {
|
|
// Make sure to add the cloned preheader and exit blocks to the parent loop
|
|
// as well.
|
|
ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI);
|
|
}
|
|
|
|
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
|
|
BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]);
|
|
// The new exit block should be in the same loop as the old one.
|
|
if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
|
|
ExitBBLoop->addBasicBlockToLoop(NewExit, *LI);
|
|
|
|
assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
|
|
"Exit block should have been split to have one successor!");
|
|
BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
|
|
|
|
// If the successor of the exit block had PHI nodes, add an entry for
|
|
// NewExit.
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator I = ExitSucc->begin();
|
|
(PN = dyn_cast<PHINode>(I)); ++I) {
|
|
Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
|
|
DenseMap<const Value *, Value*>::iterator It = ValueMap.find(V);
|
|
if (It != ValueMap.end()) V = It->second;
|
|
PN->addIncoming(V, NewExit);
|
|
}
|
|
}
|
|
|
|
// Rewrite the code to refer to itself.
|
|
for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
|
|
for (BasicBlock::iterator I = NewBlocks[i]->begin(),
|
|
E = NewBlocks[i]->end(); I != E; ++I)
|
|
RemapInstruction(I, ValueMap);
|
|
|
|
// Rewrite the original preheader to select between versions of the loop.
|
|
BranchInst *OldBR = cast<BranchInst>(OrigPreheader->getTerminator());
|
|
assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
|
|
"Preheader splitting did not work correctly!");
|
|
|
|
// Emit the new branch that selects between the two versions of this loop.
|
|
EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
|
|
LPM->deleteSimpleAnalysisValue(OldBR, L);
|
|
OldBR->eraseFromParent();
|
|
|
|
// Update dominator info
|
|
if (DF && DT) {
|
|
|
|
// Clone dominator info for all cloned basic block.
|
|
for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
|
|
BasicBlock *LBB = LoopBlocks[i];
|
|
BasicBlock *NBB = NewBlocks[i];
|
|
CloneDomInfo(NBB, LBB, NewPreheader, OrigPreheader,
|
|
OrigHeader, DT, DF, ValueMap);
|
|
|
|
// Remove any OutSiders from LBB and NBB's dominance frontier.
|
|
DominanceFrontier::iterator LBBI = DF->find(LBB);
|
|
if (LBBI != DF->end()) {
|
|
DominanceFrontier::DomSetType &LBSet = LBBI->second;
|
|
for (DominanceFrontier::DomSetType::iterator LI = LBSet.begin(),
|
|
LE = LBSet.end(); LI != LE; /* NULL */) {
|
|
BasicBlock *B = *LI++;
|
|
if (OutSiders.count(B))
|
|
DF->removeFromFrontier(LBBI, B);
|
|
}
|
|
}
|
|
|
|
// Remove any OutSiders from LBB and NBB's dominance frontier.
|
|
DominanceFrontier::iterator NBBI = DF->find(NBB);
|
|
if (NBBI != DF->end()) {
|
|
DominanceFrontier::DomSetType NBSet = NBBI->second;
|
|
for (DominanceFrontier::DomSetType::iterator NI = NBSet.begin(),
|
|
NE = NBSet.end(); NI != NE; /* NULL */) {
|
|
BasicBlock *B = *NI++;
|
|
if (OutSiders.count(B))
|
|
DF->removeFromFrontier(NBBI, B);
|
|
}
|
|
}
|
|
}
|
|
|
|
// MiddleBlocks are dominated by original pre header. SplitEdge updated
|
|
// MiddleBlocks' dominance frontier appropriately.
|
|
for (unsigned i = 0, e = MiddleBlocks.size(); i != e; ++i) {
|
|
BasicBlock *MBB = MiddleBlocks[i];
|
|
if (!MBB->getSinglePredecessor())
|
|
DT->changeImmediateDominator(MBB, OrigPreheader);
|
|
}
|
|
|
|
// All Outsiders are now dominated by original pre header.
|
|
for (SmallPtrSet<BasicBlock *, 8>::iterator OI = OutSiders.begin(),
|
|
OE = OutSiders.end(); OI != OE; ++OI) {
|
|
BasicBlock *OB = *OI;
|
|
DT->changeImmediateDominator(OB, OrigPreheader);
|
|
}
|
|
|
|
// New loop headers are dominated by original preheader
|
|
DT->changeImmediateDominator(NewBlocks[0], OrigPreheader);
|
|
DT->changeImmediateDominator(LoopBlocks[0], OrigPreheader);
|
|
}
|
|
|
|
LoopProcessWorklist.push_back(NewLoop);
|
|
redoLoop = true;
|
|
|
|
// Now we rewrite the original code to know that the condition is true and the
|
|
// new code to know that the condition is false.
|
|
RewriteLoopBodyWithConditionConstant(L , LIC, Val, false);
|
|
|
|
// It's possible that simplifying one loop could cause the other to be
|
|
// deleted. If so, don't simplify it.
|
|
if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop)
|
|
RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true);
|
|
}
|
|
|
|
/// RemoveFromWorklist - Remove all instances of I from the worklist vector
|
|
/// specified.
|
|
static void RemoveFromWorklist(Instruction *I,
|
|
std::vector<Instruction*> &Worklist) {
|
|
std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
|
|
Worklist.end(), I);
|
|
while (WI != Worklist.end()) {
|
|
unsigned Offset = WI-Worklist.begin();
|
|
Worklist.erase(WI);
|
|
WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
|
|
}
|
|
}
|
|
|
|
/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
|
|
/// program, replacing all uses with V and update the worklist.
|
|
static void ReplaceUsesOfWith(Instruction *I, Value *V,
|
|
std::vector<Instruction*> &Worklist,
|
|
Loop *L, LPPassManager *LPM) {
|
|
DOUT << "Replace with '" << *V << "': " << *I;
|
|
|
|
// Add uses to the worklist, which may be dead now.
|
|
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
|
|
if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
|
|
Worklist.push_back(Use);
|
|
|
|
// Add users to the worklist which may be simplified now.
|
|
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
|
|
UI != E; ++UI)
|
|
Worklist.push_back(cast<Instruction>(*UI));
|
|
LPM->deleteSimpleAnalysisValue(I, L);
|
|
RemoveFromWorklist(I, Worklist);
|
|
I->replaceAllUsesWith(V);
|
|
I->eraseFromParent();
|
|
++NumSimplify;
|
|
}
|
|
|
|
/// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
|
|
/// information, and remove any dead successors it has.
|
|
///
|
|
void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
|
|
std::vector<Instruction*> &Worklist,
|
|
Loop *L) {
|
|
if (pred_begin(BB) != pred_end(BB)) {
|
|
// This block isn't dead, since an edge to BB was just removed, see if there
|
|
// are any easy simplifications we can do now.
|
|
if (BasicBlock *Pred = BB->getSinglePredecessor()) {
|
|
// If it has one pred, fold phi nodes in BB.
|
|
while (isa<PHINode>(BB->begin()))
|
|
ReplaceUsesOfWith(BB->begin(),
|
|
cast<PHINode>(BB->begin())->getIncomingValue(0),
|
|
Worklist, L, LPM);
|
|
|
|
// If this is the header of a loop and the only pred is the latch, we now
|
|
// have an unreachable loop.
|
|
if (Loop *L = LI->getLoopFor(BB))
|
|
if (L->getHeader() == BB && L->contains(Pred)) {
|
|
// Remove the branch from the latch to the header block, this makes
|
|
// the header dead, which will make the latch dead (because the header
|
|
// dominates the latch).
|
|
LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L);
|
|
Pred->getTerminator()->eraseFromParent();
|
|
new UnreachableInst(Pred);
|
|
|
|
// The loop is now broken, remove it from LI.
|
|
RemoveLoopFromHierarchy(L);
|
|
|
|
// Reprocess the header, which now IS dead.
|
|
RemoveBlockIfDead(BB, Worklist, L);
|
|
return;
|
|
}
|
|
|
|
// If pred ends in a uncond branch, add uncond branch to worklist so that
|
|
// the two blocks will get merged.
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
|
|
if (BI->isUnconditional())
|
|
Worklist.push_back(BI);
|
|
}
|
|
return;
|
|
}
|
|
|
|
DOUT << "Nuking dead block: " << *BB;
|
|
|
|
// Remove the instructions in the basic block from the worklist.
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
|
|
RemoveFromWorklist(I, Worklist);
|
|
|
|
// Anything that uses the instructions in this basic block should have their
|
|
// uses replaced with undefs.
|
|
if (!I->use_empty())
|
|
I->replaceAllUsesWith(UndefValue::get(I->getType()));
|
|
}
|
|
|
|
// If this is the edge to the header block for a loop, remove the loop and
|
|
// promote all subloops.
|
|
if (Loop *BBLoop = LI->getLoopFor(BB)) {
|
|
if (BBLoop->getLoopLatch() == BB)
|
|
RemoveLoopFromHierarchy(BBLoop);
|
|
}
|
|
|
|
// Remove the block from the loop info, which removes it from any loops it
|
|
// was in.
|
|
LI->removeBlock(BB);
|
|
|
|
|
|
// Remove phi node entries in successors for this block.
|
|
TerminatorInst *TI = BB->getTerminator();
|
|
std::vector<BasicBlock*> Succs;
|
|
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
|
|
Succs.push_back(TI->getSuccessor(i));
|
|
TI->getSuccessor(i)->removePredecessor(BB);
|
|
}
|
|
|
|
// Unique the successors, remove anything with multiple uses.
|
|
std::sort(Succs.begin(), Succs.end());
|
|
Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
|
|
|
|
// Remove the basic block, including all of the instructions contained in it.
|
|
LPM->deleteSimpleAnalysisValue(BB, L);
|
|
BB->eraseFromParent();
|
|
// Remove successor blocks here that are not dead, so that we know we only
|
|
// have dead blocks in this list. Nondead blocks have a way of becoming dead,
|
|
// then getting removed before we revisit them, which is badness.
|
|
//
|
|
for (unsigned i = 0; i != Succs.size(); ++i)
|
|
if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
|
|
// One exception is loop headers. If this block was the preheader for a
|
|
// loop, then we DO want to visit the loop so the loop gets deleted.
|
|
// We know that if the successor is a loop header, that this loop had to
|
|
// be the preheader: the case where this was the latch block was handled
|
|
// above and headers can only have two predecessors.
|
|
if (!LI->isLoopHeader(Succs[i])) {
|
|
Succs.erase(Succs.begin()+i);
|
|
--i;
|
|
}
|
|
}
|
|
|
|
for (unsigned i = 0, e = Succs.size(); i != e; ++i)
|
|
RemoveBlockIfDead(Succs[i], Worklist, L);
|
|
}
|
|
|
|
/// RemoveLoopFromHierarchy - We have discovered that the specified loop has
|
|
/// become unwrapped, either because the backedge was deleted, or because the
|
|
/// edge into the header was removed. If the edge into the header from the
|
|
/// latch block was removed, the loop is unwrapped but subloops are still alive,
|
|
/// so they just reparent loops. If the loops are actually dead, they will be
|
|
/// removed later.
|
|
void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) {
|
|
LPM->deleteLoopFromQueue(L);
|
|
RemoveLoopFromWorklist(L);
|
|
}
|
|
|
|
|
|
|
|
// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
|
|
// the value specified by Val in the specified loop, or we know it does NOT have
|
|
// that value. Rewrite any uses of LIC or of properties correlated to it.
|
|
void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
|
|
Constant *Val,
|
|
bool IsEqual) {
|
|
assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
|
|
|
|
// FIXME: Support correlated properties, like:
|
|
// for (...)
|
|
// if (li1 < li2)
|
|
// ...
|
|
// if (li1 > li2)
|
|
// ...
|
|
|
|
// FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
|
|
// selects, switches.
|
|
std::vector<User*> Users(LIC->use_begin(), LIC->use_end());
|
|
std::vector<Instruction*> Worklist;
|
|
|
|
// If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
|
|
// in the loop with the appropriate one directly.
|
|
if (IsEqual || (isa<ConstantInt>(Val) && Val->getType() == Type::Int1Ty)) {
|
|
Value *Replacement;
|
|
if (IsEqual)
|
|
Replacement = Val;
|
|
else
|
|
Replacement = ConstantInt::get(Type::Int1Ty,
|
|
!cast<ConstantInt>(Val)->getZExtValue());
|
|
|
|
for (unsigned i = 0, e = Users.size(); i != e; ++i)
|
|
if (Instruction *U = cast<Instruction>(Users[i])) {
|
|
if (!L->contains(U->getParent()))
|
|
continue;
|
|
U->replaceUsesOfWith(LIC, Replacement);
|
|
Worklist.push_back(U);
|
|
}
|
|
} else {
|
|
// Otherwise, we don't know the precise value of LIC, but we do know that it
|
|
// is certainly NOT "Val". As such, simplify any uses in the loop that we
|
|
// can. This case occurs when we unswitch switch statements.
|
|
for (unsigned i = 0, e = Users.size(); i != e; ++i)
|
|
if (Instruction *U = cast<Instruction>(Users[i])) {
|
|
if (!L->contains(U->getParent()))
|
|
continue;
|
|
|
|
Worklist.push_back(U);
|
|
|
|
// If we know that LIC is not Val, use this info to simplify code.
|
|
if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) {
|
|
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
|
|
if (SI->getCaseValue(i) == Val) {
|
|
// Found a dead case value. Don't remove PHI nodes in the
|
|
// successor if they become single-entry, those PHI nodes may
|
|
// be in the Users list.
|
|
|
|
// FIXME: This is a hack. We need to keep the successor around
|
|
// and hooked up so as to preserve the loop structure, because
|
|
// trying to update it is complicated. So instead we preserve the
|
|
// loop structure and put the block on an dead code path.
|
|
|
|
BasicBlock* Old = SI->getParent();
|
|
BasicBlock* Split = SplitBlock(Old, SI, this);
|
|
|
|
Instruction* OldTerm = Old->getTerminator();
|
|
new BranchInst(Split, SI->getSuccessor(i),
|
|
ConstantInt::getTrue(), OldTerm);
|
|
|
|
LPM->deleteSimpleAnalysisValue(Old->getTerminator(), L);
|
|
Old->getTerminator()->eraseFromParent();
|
|
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator II = SI->getSuccessor(i)->begin();
|
|
(PN = dyn_cast<PHINode>(II)); ++II) {
|
|
Value *InVal = PN->removeIncomingValue(Split, false);
|
|
PN->addIncoming(InVal, Old);
|
|
}
|
|
|
|
SI->removeCase(i);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// TODO: We could do other simplifications, for example, turning
|
|
// LIC == Val -> false.
|
|
}
|
|
}
|
|
|
|
SimplifyCode(Worklist, L);
|
|
}
|
|
|
|
/// SimplifyCode - Okay, now that we have simplified some instructions in the
|
|
/// loop, walk over it and constant prop, dce, and fold control flow where
|
|
/// possible. Note that this is effectively a very simple loop-structure-aware
|
|
/// optimizer. During processing of this loop, L could very well be deleted, so
|
|
/// it must not be used.
|
|
///
|
|
/// FIXME: When the loop optimizer is more mature, separate this out to a new
|
|
/// pass.
|
|
///
|
|
void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
|
|
while (!Worklist.empty()) {
|
|
Instruction *I = Worklist.back();
|
|
Worklist.pop_back();
|
|
|
|
// Simple constant folding.
|
|
if (Constant *C = ConstantFoldInstruction(I)) {
|
|
ReplaceUsesOfWith(I, C, Worklist, L, LPM);
|
|
continue;
|
|
}
|
|
|
|
// Simple DCE.
|
|
if (isInstructionTriviallyDead(I)) {
|
|
DOUT << "Remove dead instruction '" << *I;
|
|
|
|
// Add uses to the worklist, which may be dead now.
|
|
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
|
|
if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
|
|
Worklist.push_back(Use);
|
|
LPM->deleteSimpleAnalysisValue(I, L);
|
|
RemoveFromWorklist(I, Worklist);
|
|
I->eraseFromParent();
|
|
++NumSimplify;
|
|
continue;
|
|
}
|
|
|
|
// Special case hacks that appear commonly in unswitched code.
|
|
switch (I->getOpcode()) {
|
|
case Instruction::Select:
|
|
if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(0))) {
|
|
ReplaceUsesOfWith(I, I->getOperand(!CB->getZExtValue()+1), Worklist, L,
|
|
LPM);
|
|
continue;
|
|
}
|
|
break;
|
|
case Instruction::And:
|
|
if (isa<ConstantInt>(I->getOperand(0)) &&
|
|
I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS
|
|
cast<BinaryOperator>(I)->swapOperands();
|
|
if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1)))
|
|
if (CB->getType() == Type::Int1Ty) {
|
|
if (CB->isOne()) // X & 1 -> X
|
|
ReplaceUsesOfWith(I, I->getOperand(0), Worklist, L, LPM);
|
|
else // X & 0 -> 0
|
|
ReplaceUsesOfWith(I, I->getOperand(1), Worklist, L, LPM);
|
|
continue;
|
|
}
|
|
break;
|
|
case Instruction::Or:
|
|
if (isa<ConstantInt>(I->getOperand(0)) &&
|
|
I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS
|
|
cast<BinaryOperator>(I)->swapOperands();
|
|
if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1)))
|
|
if (CB->getType() == Type::Int1Ty) {
|
|
if (CB->isOne()) // X | 1 -> 1
|
|
ReplaceUsesOfWith(I, I->getOperand(1), Worklist, L, LPM);
|
|
else // X | 0 -> X
|
|
ReplaceUsesOfWith(I, I->getOperand(0), Worklist, L, LPM);
|
|
continue;
|
|
}
|
|
break;
|
|
case Instruction::Br: {
|
|
BranchInst *BI = cast<BranchInst>(I);
|
|
if (BI->isUnconditional()) {
|
|
// If BI's parent is the only pred of the successor, fold the two blocks
|
|
// together.
|
|
BasicBlock *Pred = BI->getParent();
|
|
BasicBlock *Succ = BI->getSuccessor(0);
|
|
BasicBlock *SinglePred = Succ->getSinglePredecessor();
|
|
if (!SinglePred) continue; // Nothing to do.
|
|
assert(SinglePred == Pred && "CFG broken");
|
|
|
|
DOUT << "Merging blocks: " << Pred->getName() << " <- "
|
|
<< Succ->getName() << "\n";
|
|
|
|
// Resolve any single entry PHI nodes in Succ.
|
|
while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
|
|
ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
|
|
|
|
// Move all of the successor contents from Succ to Pred.
|
|
Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
|
|
Succ->end());
|
|
LPM->deleteSimpleAnalysisValue(BI, L);
|
|
BI->eraseFromParent();
|
|
RemoveFromWorklist(BI, Worklist);
|
|
|
|
// If Succ has any successors with PHI nodes, update them to have
|
|
// entries coming from Pred instead of Succ.
|
|
Succ->replaceAllUsesWith(Pred);
|
|
|
|
// Remove Succ from the loop tree.
|
|
LI->removeBlock(Succ);
|
|
LPM->deleteSimpleAnalysisValue(Succ, L);
|
|
Succ->eraseFromParent();
|
|
++NumSimplify;
|
|
} else if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){
|
|
// Conditional branch. Turn it into an unconditional branch, then
|
|
// remove dead blocks.
|
|
break; // FIXME: Enable.
|
|
|
|
DOUT << "Folded branch: " << *BI;
|
|
BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue());
|
|
BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue());
|
|
DeadSucc->removePredecessor(BI->getParent(), true);
|
|
Worklist.push_back(new BranchInst(LiveSucc, BI));
|
|
LPM->deleteSimpleAnalysisValue(BI, L);
|
|
BI->eraseFromParent();
|
|
RemoveFromWorklist(BI, Worklist);
|
|
++NumSimplify;
|
|
|
|
RemoveBlockIfDead(DeadSucc, Worklist, L);
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|