Improved compile time:

1. Size heuristics changed. Now we calculate number of unswitching
branches only once per loop.
2. Some checks was moved from UnswitchIfProfitable to
processCurrentLoop, since it is not changed during processCurrentLoop
iteration. It allows decide to skip some loops at an early stage.
Extended statistics:
- Added total number of instructions analyzed.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147935 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LoopUnswitch.cpp

@@ -56,12 +56,13 @@ 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");
+STATISTIC(TotalInsts,  "Total number of instructions analyzed");
 
 // The specific value of 50 here was chosen based only on intuition and a
 // few specific examples.
 static cl::opt<unsigned>
 Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
-          cl::init(50), cl::Hidden);
+          cl::init(100), cl::Hidden);
   
 namespace {
   class LoopUnswitch : public LoopPass {
@@ -72,6 +73,18 @@ namespace {
     // after RewriteLoopBodyWithConditionConstant rewrites first loop.
     std::vector<Loop*> LoopProcessWorklist;
     
+    struct LoopProperties {
+      unsigned CanBeUnswitchedCount;
+      unsigned SizeEstimation;
+    };
+    
+    typedef DenseMap<const Loop*, LoopProperties> LoopPropsMap;
+    typedef LoopPropsMap::iterator LoopPropsMapIt;
+    LoopPropsMap LoopsProperties;
+    
+    // Max size of code we can produce on remained iterations.
+    unsigned MaxSize;
+    
     // FIXME: Consider custom class for this.
     std::map<const SwitchInst*, SmallPtrSet<const Value *,8> > UnswitchedVals;
     
@@ -93,7 +106,7 @@ namespace {
   public:
     static char ID; // Pass ID, replacement for typeid
     explicit LoopUnswitch(bool Os = false) : 
-      LoopPass(ID), OptimizeForSize(Os), redoLoop(false), 
+      LoopPass(ID), MaxSize(Threshold), OptimizeForSize(Os), redoLoop(false), 
       currentLoop(NULL), DT(NULL), loopHeader(NULL),
       loopPreheader(NULL) {
         initializeLoopUnswitchPass(*PassRegistry::getPassRegistry());
@@ -119,6 +132,15 @@ namespace {
   private:
 
     virtual void releaseMemory() {
+      
+      LoopPropsMapIt LIt = LoopsProperties.find(currentLoop);
+
+      if (LIt != LoopsProperties.end()) {
+        LoopProperties& Props = LIt->second;
+        MaxSize += Props.CanBeUnswitchedCount * Props.SizeEstimation;
+        LoopsProperties.erase(LIt);
+      }
+      
       // 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.
@@ -143,7 +165,10 @@ namespace {
     /// already unswitched and has redundant successors.
     /// Note, that new loop data is stored inside the VMap.
     void CloneUnswitchedVals(const ValueToValueMapTy& VMap,
-                                    const BasicBlock* SrcBB);     
+                                    const BasicBlock* SrcBB);
+    
+    bool CountLoop(const Loop* L);
+    void CloneLoopProperties(const Loop* NewLoop, const Loop* OldLoop);
 
     void initLoopData() {
       loopHeader = currentLoop->getHeader();
@@ -193,6 +218,10 @@ Pass *llvm::createLoopUnswitchPass(bool Os) {
 /// invariant in the loop, or has an invariant piece, return the invariant.
 /// Otherwise, return null.
 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
+  
+  // We started analyze new instruction, increment scanned instructions counter.
+  ++TotalInsts;
+  
   // We can never unswitch on vector conditions.
   if (Cond->getType()->isVectorTy())
     return 0;
@@ -246,7 +275,19 @@ bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
 /// and profitable.
 bool LoopUnswitch::processCurrentLoop() {
   bool Changed = false;
-  LLVMContext &Context = currentLoop->getHeader()->getContext();
+
+  initLoopData();
+  
+  // If LoopSimplify was unable to form a preheader, don't do any unswitching.
+  if (!loopPreheader)
+    return false;
+  
+  LLVMContext &Context = loopHeader->getContext();
+  
+  // Probably we reach the quota of branches for this loop. If so
+  // stop unswitching.
+  if (!CountLoop(currentLoop))
+    return 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
@@ -332,6 +373,58 @@ void LoopUnswitch::CloneUnswitchedVals(const ValueToValueMapTy& VMap,
   }
 }
 
+bool LoopUnswitch::CountLoop(const Loop* L) {
+  std::pair<LoopPropsMapIt, bool> InsertRes =
+      LoopsProperties.insert(std::make_pair(L, LoopProperties()));
+  
+  LoopProperties& Props = InsertRes.first->second;
+   
+  if (InsertRes.second) {
+    // New loop.
+
+    // Limit the number of instructions to avoid causing significant code
+    // 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.
+    
+    // FIXME: This is overly conservative because it does not take into
+    // consideration code simplification opportunities and code that can
+    // be shared by the resultant unswitched loops.
+    CodeMetrics Metrics;
+    for (Loop::block_iterator I = L->block_begin(), 
+           E = L->block_end();
+         I != E; ++I)
+      Metrics.analyzeBasicBlock(*I);    
+
+    Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5);
+    Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
+    MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount;
+  }
+   
+  if (!Props.CanBeUnswitchedCount) {
+    DEBUG(dbgs() << "NOT unswitching loop %"
+          << L->getHeader()->getName() << ", cost too high: "
+          << L->getBlocks().size() << "\n");
+    
+    return false;
+  }
+  return true;
+}
+
+void LoopUnswitch::CloneLoopProperties(
+    const Loop* NewLoop, const Loop* OldLoop) {
+  
+  LoopProperties& OldLoopProps = LoopsProperties[OldLoop];
+  LoopProperties& NewLoopProps = LoopsProperties[NewLoop];
+  
+  --OldLoopProps.CanBeUnswitchedCount;
+  unsigned Quota = OldLoopProps.CanBeUnswitchedCount;
+  NewLoopProps.CanBeUnswitchedCount = Quota / 2;
+  OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2;
+  
+  NewLoopProps.SizeEstimation = OldLoopProps.SizeEstimation;  
+}
+
 /// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
 /// loop with no side effects (including infinite loops).
 ///
@@ -468,12 +561,6 @@ bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
 /// unswitch the loop, reprocess the pieces, then return true.
 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
 
-  initLoopData();
-
-  // If LoopSimplify was unable to form a preheader, don't do any unswitching.
-  if (!loopPreheader)
-    return false;
-
   Function *F = loopHeader->getParent();
 
   Constant *CondVal = 0;
@@ -491,34 +578,6 @@ bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
   if (OptimizeForSize || F->hasFnAttr(Attribute::OptimizeForSize))
     return false;
 
-  // FIXME: This is overly conservative because it does not take into
-  // consideration code simplification opportunities and code that can
-  // be shared by the resultant unswitched loops.
-  CodeMetrics Metrics;
-  for (Loop::block_iterator I = currentLoop->block_begin(), 
-         E = currentLoop->block_end();
-       I != E; ++I)
-    Metrics.analyzeBasicBlock(*I);
-
-  // Limit the number of instructions to avoid causing significant code
-  // 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.
-  
-  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: "
-          << currentLoop->getBlocks().size() << "\n");
-    return false;
-  }
-
   UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
   return true;
 }
@@ -701,6 +760,7 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
 
   // Now we create the new Loop object for the versioned loop.
   Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM);
+  CloneLoopProperties(NewLoop, L);
   Loop *ParentLoop = L->getParentLoop();
   if (ParentLoop) {
     // Make sure to add the cloned preheader and exit blocks to the parent loop

test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches-Threshold.ll

@@ -1,5 +1,5 @@
-; RUN: opt -loop-unswitch -loop-unswitch-threshold 30 -disable-output -stats -info-output-file - < %s | FileCheck --check-prefix=STATS %s
-; RUN: opt -S -loop-unswitch -loop-unswitch-threshold 30 -verify-loop-info -verify-dom-info %s | FileCheck %s
+; RUN: opt -loop-unswitch -loop-unswitch-threshold 13 -disable-output -stats -info-output-file - < %s | FileCheck --check-prefix=STATS %s
+; RUN: opt -S -loop-unswitch -loop-unswitch-threshold 13 -verify-loop-info -verify-dom-info %s | FileCheck %s
 
 ; STATS: 1 loop-simplify - Number of pre-header or exit blocks inserted
 ; STATS: 1 loop-unswitch - Number of switches unswitched