[ScalarEvolution] Refactor forgetLoop() to improve performance
forgetLoop() has pretty bad performance because it goes over
the same instructions over and over again in particular when
nested loop are involved.
The refactoring changes the function to a not-recursive function
and reusing the allocation for data-structures and the Visited
set.
NFCI
Differential Revision: https://reviews.llvm.org/D37659
llvm-svn: 312920
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 73ce83e..640d80a 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6353,7 +6353,7 @@
void ScalarEvolution::forgetLoop(const Loop *L) {
// Drop any stored trip count value.
auto RemoveLoopFromBackedgeMap =
- [L](DenseMap<const Loop *, BackedgeTakenInfo> &Map) {
+ [](DenseMap<const Loop *, BackedgeTakenInfo> &Map, const Loop *L) {
auto BTCPos = Map.find(L);
if (BTCPos != Map.end()) {
BTCPos->second.clear();
@@ -6361,53 +6361,58 @@
}
};
- RemoveLoopFromBackedgeMap(BackedgeTakenCounts);
- RemoveLoopFromBackedgeMap(PredicatedBackedgeTakenCounts);
+ SmallVector<const Loop *, 16> LoopWorklist(1, L);
+ SmallVector<Instruction *, 32> Worklist;
+ SmallPtrSet<Instruction *, 16> Visited;
- // Drop information about predicated SCEV rewrites for this loop.
- for (auto I = PredicatedSCEVRewrites.begin();
- I != PredicatedSCEVRewrites.end();) {
- std::pair<const SCEV *, const Loop *> Entry = I->first;
- if (Entry.second == L)
- PredicatedSCEVRewrites.erase(I++);
- else
- ++I;
- }
+ // Iterate over all the loops and sub-loops to drop SCEV information.
+ while (!LoopWorklist.empty()) {
+ auto *CurrL = LoopWorklist.pop_back_val();
- // Drop information about expressions based on loop-header PHIs.
- SmallVector<Instruction *, 16> Worklist;
- PushLoopPHIs(L, Worklist);
+ RemoveLoopFromBackedgeMap(BackedgeTakenCounts, CurrL);
+ RemoveLoopFromBackedgeMap(PredicatedBackedgeTakenCounts, CurrL);
- SmallPtrSet<Instruction *, 8> Visited;
- while (!Worklist.empty()) {
- Instruction *I = Worklist.pop_back_val();
- if (!Visited.insert(I).second)
- continue;
-
- ValueExprMapType::iterator It =
- ValueExprMap.find_as(static_cast<Value *>(I));
- if (It != ValueExprMap.end()) {
- eraseValueFromMap(It->first);
- forgetMemoizedResults(It->second);
- if (PHINode *PN = dyn_cast<PHINode>(I))
- ConstantEvolutionLoopExitValue.erase(PN);
+ // Drop information about predicated SCEV rewrites for this loop.
+ for (auto I = PredicatedSCEVRewrites.begin();
+ I != PredicatedSCEVRewrites.end();) {
+ std::pair<const SCEV *, const Loop *> Entry = I->first;
+ if (Entry.second == CurrL)
+ PredicatedSCEVRewrites.erase(I++);
+ else
+ ++I;
}
- PushDefUseChildren(I, Worklist);
+ // Drop information about expressions based on loop-header PHIs.
+ PushLoopPHIs(CurrL, Worklist);
+
+ while (!Worklist.empty()) {
+ Instruction *I = Worklist.pop_back_val();
+ if (!Visited.insert(I).second)
+ continue;
+
+ ValueExprMapType::iterator It =
+ ValueExprMap.find_as(static_cast<Value *>(I));
+ if (It != ValueExprMap.end()) {
+ eraseValueFromMap(It->first);
+ forgetMemoizedResults(It->second);
+ if (PHINode *PN = dyn_cast<PHINode>(I))
+ ConstantEvolutionLoopExitValue.erase(PN);
+ }
+
+ PushDefUseChildren(I, Worklist);
+ }
+
+ for (auto I = ExitLimits.begin(); I != ExitLimits.end(); ++I) {
+ auto &Query = I->first;
+ if (Query.L == CurrL)
+ ExitLimits.erase(I);
+ }
+
+ LoopPropertiesCache.erase(CurrL);
+ // Forget all contained loops too, to avoid dangling entries in the
+ // ValuesAtScopes map.
+ LoopWorklist.append(CurrL->begin(), CurrL->end());
}
-
- for (auto I = ExitLimits.begin(); I != ExitLimits.end(); ++I) {
- auto &Query = I->first;
- if (Query.L == L)
- ExitLimits.erase(I);
- }
-
- // Forget all contained loops too, to avoid dangling entries in the
- // ValuesAtScopes map.
- for (Loop *I : *L)
- forgetLoop(I);
-
- LoopPropertiesCache.erase(L);
}
void ScalarEvolution::forgetValue(Value *V) {