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Add the actual code for r147175. 

llvm-svn: 147176
This commit is contained in:
Chad Rosier 2011-12-22 21:10:46 +00:00
parent 388769427d
commit 3ba90a1655
1 changed files with 82 additions and 11 deletions
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93
llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
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@ -71,7 +71,9 @@ namespace {
// LoopProcessWorklist - Used to check if second loop needs processing
// after RewriteLoopBodyWithConditionConstant rewrites first loop.
std::vector<Loop*> LoopProcessWorklist;
SmallPtrSet<Value *,8> UnswitchedVals;
// FIXME: Consider custom class for this.
std::map<const SwitchInst*, SmallPtrSet<const Value *,8> > UnswitchedVals;
bool OptimizeForSize;
bool redoLoop;
@ -117,7 +119,15 @@ namespace {
private:
virtual void releaseMemory() {
UnswitchedVals.clear();
// We need to forget about all switches in the current loop.
// FIXME: Do it better than enumerating all blocks of code
// and see if it is a switch instruction.
for (Loop::block_iterator I = currentLoop->block_begin(),
E = currentLoop->block_end(); I != E; ++I) {
SwitchInst* SI = dyn_cast<SwitchInst>((*I)->getTerminator());
if (SI)
UnswitchedVals.erase(SI);
}
}
/// RemoveLoopFromWorklist - If the specified loop is on the loop worklist,
@ -128,6 +138,12 @@ namespace {
if (I != LoopProcessWorklist.end())
LoopProcessWorklist.erase(I);
}
/// For new loop switches we clone info about values that was
/// already unswitched and has redundant successors.
/// Note, that new loop data is stored inside the VMap.
void CloneUnswitchedVals(const ValueToValueMapTy& VMap,
const BasicBlock* SrcBB);
void initLoopData() {
loopHeader = currentLoop->getHeader();
@ -255,13 +271,25 @@ bool LoopUnswitch::processCurrentLoop() {
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
currentLoop, Changed);
if (LoopCond && SI->getNumCases() > 1) {
unsigned NumCases = SI->getNumCases();
if (LoopCond && NumCases > 1) {
// Find a value to unswitch on:
// FIXME: this should chose the most expensive case!
// FIXME: scan for a case with a non-critical edge?
Constant *UnswitchVal = SI->getCaseValue(1);
Constant *UnswitchVal = NULL;
// Do not process same value again and again.
if (!UnswitchedVals.insert(UnswitchVal))
// At this point we have some cases already unswitched and
// some not yet unswitched. Let's find the first not yet unswitched one.
for (unsigned i = 1; i < NumCases; ++i) {
Constant* UnswitchValCandidate = SI->getCaseValue(i);
if (!UnswitchedVals[SI].count(UnswitchValCandidate)) {
UnswitchVal = UnswitchValCandidate;
break;
}
}
if (!UnswitchVal)
continue;
if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
@ -287,6 +315,23 @@ bool LoopUnswitch::processCurrentLoop() {
return Changed;
}
/// For new loop switches we clone info about values that was
/// already unswitched and has redundant successors.
/// Not that new loop data is stored inside the VMap.
void LoopUnswitch::CloneUnswitchedVals(const ValueToValueMapTy& VMap,
const BasicBlock* SrcBB) {
const SwitchInst* SI = dyn_cast<SwitchInst>(SrcBB->getTerminator());
if (SI && UnswitchedVals.count(SI)) {
// Don't clone a totally simplified switch.
if (isa<Constant>(SI->getCondition()))
return;
Value* I = VMap.lookup(SI);
assert(I && "All instructions that are in SrcBB must be in VMap.");
UnswitchedVals[cast<SwitchInst>(I)] = UnswitchedVals[SI];
}
}
/// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
/// loop with no side effects (including infinite loops).
///
@ -378,14 +423,25 @@ bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
// 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(currentLoop,
// this.
// Note that we can't trivially unswitch on the default case or
// on already unswitched cases.
for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
BasicBlock* LoopExitCandidate;
if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
SI->getSuccessor(i)))) {
// Okay, we found a trivial case, remember the value that is trivial.
if (Val) *Val = SI->getCaseValue(i);
ConstantInt* CaseVal = SI->getCaseValue(i);
// Check that it was not unswitched before, since already unswitched
// trivial vals are looks trivial too.
if (UnswitchedVals[SI].count(CaseVal))
continue;
LoopExitBB = LoopExitCandidate;
if (Val) *Val = CaseVal;
break;
}
}
}
// If we didn't find a single unique LoopExit block, or if the loop exit block
@ -447,8 +503,14 @@ bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
// expansion, and the number of basic blocks, to avoid loops with
// large numbers of branches which cause loop unswitching to go crazy.
// This is a very ad-hoc heuristic.
if (Metrics.NumInsts > Threshold ||
Metrics.NumBlocks * 5 > Threshold ||
unsigned NumUnswitched =
(NumSwitches + NumBranches) + 1 /*take in account current iteration*/;
unsigned NumInsts = Metrics.NumInsts * NumUnswitched;
unsigned NumBlocks = Metrics.NumBlocks * NumUnswitched;
if (NumInsts > Threshold || NumBlocks * 5 > Threshold ||
Metrics.containsIndirectBr || Metrics.isRecursive) {
DEBUG(dbgs() << "NOT unswitching loop %"
<< currentLoop->getHeader()->getName() << ", cost too high: "
@ -620,6 +682,12 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
ValueToValueMapTy VMap;
for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F);
// Inherit simplified switches info for NewBB
// We needn't pass NewBB since its instructions are already contained
// inside the VMap.
CloneUnswitchedVals(VMap, LoopBlocks[i]);
NewBlocks.push_back(NewBB);
VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping.
LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L);
@ -945,6 +1013,9 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
BasicBlock *Switch = SI->getParent();
BasicBlock *SISucc = SI->getSuccessor(DeadCase);
BasicBlock *Latch = L->getLoopLatch();
UnswitchedVals[SI].insert(Val);
if (!SI->findCaseDest(SISucc)) continue; // Edge is critical.
// If the DeadCase successor dominates the loop latch, then the
// transformation isn't safe since it will delete the sole predecessor edge