[NFC] ScalarEvolution: apply SSO to the ExprValueMap value

ExprValueMap is a map from SCEV * to a set-vector of (Value *, ConstantInt *) pair,
and while the map itself will likely be big-ish (have many keys),
it is a reasonable assumption that each key will refer to a small-ish
number of pairs.

In particular looking at n=512 case from
https://bugs.llvm.org/show_bug.cgi?id=50384,
the small-size of 4 appears to be the sweet spot,
it results in the least allocations while minimizing memory footprint.
```
$ for i in $(ls heaptrack.opt.*.gz); do echo $i; heaptrack_print $i | tail -n 6; echo ""; done
heaptrack.opt.0-orig.gz
total runtime: 14.32s.
calls to allocation functions: 8222442 (574192/s)
temporary memory allocations: 2419000 (168924/s)
peak heap memory consumption: 190.98MB
peak RSS (including heaptrack overhead): 239.65MB
total memory leaked: 67.58KB

heaptrack.opt.1-n1.gz
total runtime: 13.72s.
calls to allocation functions: 7184188 (523705/s)
temporary memory allocations: 2419017 (176338/s)
peak heap memory consumption: 191.38MB
peak RSS (including heaptrack overhead): 239.64MB
total memory leaked: 67.58KB

heaptrack.opt.2-n2.gz
total runtime: 12.24s.
calls to allocation functions: 6146827 (502355/s)
temporary memory allocations: 2418997 (197695/s)
peak heap memory consumption: 163.31MB
peak RSS (including heaptrack overhead): 211.01MB
total memory leaked: 67.58KB

heaptrack.opt.3-n4.gz
total runtime: 12.28s.
calls to allocation functions: 6068532 (494260/s)
temporary memory allocations: 2418985 (197017/s)
peak heap memory consumption: 155.43MB
peak RSS (including heaptrack overhead): 201.77MB
total memory leaked: 67.58KB

heaptrack.opt.4-n8.gz
total runtime: 12.06s.
calls to allocation functions: 6068042 (503321/s)
temporary memory allocations: 2418992 (200646/s)
peak heap memory consumption: 166.03MB
peak RSS (including heaptrack overhead): 213.55MB
total memory leaked: 67.58KB

heaptrack.opt.5-n16.gz
total runtime: 12.14s.
calls to allocation functions: 6067993 (499958/s)
temporary memory allocations: 2418999 (199307/s)
peak heap memory consumption: 187.24MB
peak RSS (including heaptrack overhead): 233.69MB
total memory leaked: 67.58KB
```

While that test may be an edge worst-case scenario,
https://llvm-compile-time-tracker.com/compare.php?from=dee85d47d9f15fc268f7b18f279dac2774836615&to=98a57e31b1947d5bcdf4a5605ac2ab32b4bd5f63&stat=instructions
agrees that this also results in improvements in the usual situations.

diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index a336211..bddd2cf 100644 (file)
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1255,7 +1255,8 @@ private:
 
   /// The type for ExprValueMap.
   using ValueOffsetPair = std::pair<Value *, ConstantInt *>;
-  using ExprValueMapType = DenseMap<const SCEV *, SetVector<ValueOffsetPair>>;
+  using ValueOffsetPairSetVector = SmallSetVector<ValueOffsetPair, 4>;
+  using ExprValueMapType = DenseMap<const SCEV *, ValueOffsetPairSetVector>;
 
   /// ExprValueMap -- This map records the original values from which
   /// the SCEV expr is generated from.
@@ -1307,7 +1308,7 @@ private:
   DenseMap<const SCEV *, uint32_t> MinTrailingZerosCache;
 
   /// Return the Value set from which the SCEV expr is generated.
-  SetVector<ValueOffsetPair> *getSCEVValues(const SCEV *S);
+  ValueOffsetPairSetVector *getSCEVValues(const SCEV *S);
 
   /// Private helper method for the GetMinTrailingZeros method
   uint32_t GetMinTrailingZerosImpl(const SCEV *S);

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 872c515..84671f5 100644 (file)
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3832,7 +3832,7 @@ static std::pair<const SCEV *, ConstantInt *> splitAddExpr(const SCEV *S) {
 
 /// Return the ValueOffsetPair set for \p S. \p S can be represented
 /// by the value and offset from any ValueOffsetPair in the set.
-SetVector<ScalarEvolution::ValueOffsetPair> *
+ScalarEvolution::ValueOffsetPairSetVector *
 ScalarEvolution::getSCEVValues(const SCEV *S) {
   ExprValueMapType::iterator SI = ExprValueMap.find_as(S);
   if (SI == ExprValueMap.end())
@@ -3855,7 +3855,7 @@ void ScalarEvolution::eraseValueFromMap(Value *V) {
   if (I != ValueExprMap.end()) {
     const SCEV *S = I->second;
     // Remove {V, 0} from the set of ExprValueMap[S]
-    if (SetVector<ValueOffsetPair> *SV = getSCEVValues(S))
+    if (auto *SV = getSCEVValues(S))
       SV->remove({V, nullptr});
 
     // Remove {V, Offset} from the set of ExprValueMap[Stripped]
@@ -3863,7 +3863,7 @@ void ScalarEvolution::eraseValueFromMap(Value *V) {
     ConstantInt *Offset;
     std::tie(Stripped, Offset) = splitAddExpr(S);
     if (Offset != nullptr) {
-      if (SetVector<ValueOffsetPair> *SV = getSCEVValues(Stripped))
+      if (auto *SV = getSCEVValues(Stripped))
         SV->remove({V, Offset});
     }
     ValueExprMap.erase(V);

diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index 815f7b1..42f27bc 100644 (file)
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -1887,7 +1887,7 @@ Value *SCEVExpander::expandCodeForImpl(const SCEV *SH, Type *Ty, bool Root) {
 ScalarEvolution::ValueOffsetPair
 SCEVExpander::FindValueInExprValueMap(const SCEV *S,
                                       const Instruction *InsertPt) {
-  SetVector<ScalarEvolution::ValueOffsetPair> *Set = SE.getSCEVValues(S);
+  auto *Set = SE.getSCEVValues(S);
   // If the expansion is not in CanonicalMode, and the SCEV contains any
   // sub scAddRecExpr type SCEV, it is required to expand the SCEV literally.
   if (CanonicalMode || !SE.containsAddRecurrence(S)) {