[llvm-commits] [llvm] r147176 - /llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp
Chad Rosier
mcrosier at apple.com
Thu Dec 22 13:10:46 PST 2011
Author: mcrosier
Date: Thu Dec 22 15:10:46 2011
New Revision: 147176
URL: http://llvm.org/viewvc/llvm-project?rev=147176&view=rev
Log:
Add the actual code for r147175.
Modified:
llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp?rev=147176&r1=147175&r2=147176&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp Thu Dec 22 15:10:46 2011
@@ -71,7 +71,9 @@
// 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 @@
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 @@
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 @@
} 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 @@
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 @@
// 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 @@
// 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 @@
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 @@
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
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