Change data structure to memorize computed result in ScalarEvolution

Replace std::map with SmallVector to memorize the cached result since SCEV usually belongs to little Loop/BB
Linear scan on SmallVector is faster than std::map.

Code reviewer : Andrew Trick.
Test result   : Pass Unit Test & LLVM Test Suite

401.bzip2	0.425721	0.419981	101.37%
403.gcc		24.53855	24.2667		101.12%
429.mcf		0.060847	0.059944	101.51%
433.milc	0.646009	0.636119	101.55%
444.namd	1.383928	1.370614	100.97%
445.gobmk	5.836575	5.800225	100.63%
450.soplex	1.911257	1.895963	100.81%
456.hmmer	1.039565	1.032534	100.68%
458.sjeng	0.897401	0.885567	101.34%
464.h264ref	3.645908	3.577991	101.90%
470.lbm		0.049456	0.048398	102.19%
471.omnetpp	5.638575	5.60435		100.61%
bitmnp01	0.045738	0.045291	100.99%
cjpegv2data	0.304359	0.302833	100.50%
idctrn01	0.046433	0.045763	101.46%
quake2		4.534416	4.4952		100.87%
quake		2.688566	2.659208	101.10%
xcsoar		12.42545	12.30385	100.99%
linpack		0.038739	0.03803		101.86%
matrix01	0.053564	0.0528		101.45%
nbench		0.402867	0.395803	101.78%
tblook01	0.021265	0.021015	101.19%
ttsprk01	0.066384	0.065566	101.25%

llvm-svn: 194459

2 files changed, 45 insertions, 25 deletions

diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 4915bc6af20..944b1447b45 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -361,18 +361,18 @@ namespace llvm {
     /// that we attempt to compute getSCEVAtScope information for, which can
     /// be expensive in extreme cases.
     DenseMap<const SCEV *,
-             std::map<const Loop *, const SCEV *> > ValuesAtScopes;
+             SmallVector<std::pair<const Loop *, const SCEV *>, 2> > ValuesAtScopes;
 
     /// LoopDispositions - Memoized computeLoopDisposition results.
     DenseMap<const SCEV *,
-             std::map<const Loop *, LoopDisposition> > LoopDispositions;
+             SmallVector<std::pair<const Loop *, LoopDisposition>, 2> > LoopDispositions;
 
     /// computeLoopDisposition - Compute a LoopDisposition value.
     LoopDisposition computeLoopDisposition(const SCEV *S, const Loop *L);
 
     /// BlockDispositions - Memoized computeBlockDisposition results.
     DenseMap<const SCEV *,
-             std::map<const BasicBlock *, BlockDisposition> > BlockDispositions;
+             SmallVector<std::pair<const BasicBlock *, BlockDisposition>, 2> > BlockDispositions;
 
     /// computeBlockDisposition - Compute a BlockDisposition value.
     BlockDisposition computeBlockDisposition(const SCEV *S, const BasicBlock *BB);
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 9467823ddc0..37be5db7e67 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5059,15 +5059,21 @@ const SCEV *ScalarEvolution::ComputeExitCountExhaustively(const Loop *L,
 /// original value V is returned.
 const SCEV *ScalarEvolution::getSCEVAtScope(const SCEV *V, const Loop *L) {
   // Check to see if we've folded this expression at this loop before.
-  std::map<const Loop *, const SCEV *> &Values = ValuesAtScopes[V];
-  std::pair<std::map<const Loop *, const SCEV *>::iterator, bool> Pair =
-    Values.insert(std::make_pair(L, static_cast<const SCEV *>(0)));
-  if (!Pair.second)
-    return Pair.first->second ? Pair.first->second : V;
-
+  SmallVector<std::pair<const Loop *, const SCEV *>, 2> &Values = ValuesAtScopes[V];
+  for (unsigned u = 0; u < Values.size(); u++) {
+    if (Values[u].first == L)
+      return Values[u].second ? Values[u].second : V;
+  }
+  Values.push_back(std::make_pair(L, static_cast<const SCEV *>(0)));
   // Otherwise compute it.
   const SCEV *C = computeSCEVAtScope(V, L);
-  ValuesAtScopes[V][L] = C;
+  SmallVector<std::pair<const Loop *, const SCEV *>, 2> &Values2 = ValuesAtScopes[V];
+  for (unsigned u = Values2.size(); u > 0; u--) {
+    if (Values2[u - 1].first == L) {
+      Values2[u - 1].second = C;
+      break;
+    }
+  }
   return C;
 }
 
@@ -6727,7 +6733,7 @@ ScalarEvolution::SCEVCallbackVH::SCEVCallbackVH(Value *V, ScalarEvolution *se)
 //===----------------------------------------------------------------------===//
 
 ScalarEvolution::ScalarEvolution()
-  : FunctionPass(ID), FirstUnknown(0) {
+  : FunctionPass(ID), ValuesAtScopes(64), LoopDispositions(64), BlockDispositions(64), FirstUnknown(0) {
   initializeScalarEvolutionPass(*PassRegistry::getPassRegistry());
 }
 
@@ -6865,14 +6871,21 @@ void ScalarEvolution::print(raw_ostream &OS, const Module *) const {
 
 ScalarEvolution::LoopDisposition
 ScalarEvolution::getLoopDisposition(const SCEV *S, const Loop *L) {
-  std::map<const Loop *, LoopDisposition> &Values = LoopDispositions[S];
-  std::pair<std::map<const Loop *, LoopDisposition>::iterator, bool> Pair =
-    Values.insert(std::make_pair(L, LoopVariant));
-  if (!Pair.second)
-    return Pair.first->second;
-
+  SmallVector<std::pair<const Loop *, LoopDisposition>, 2> &Values = LoopDispositions[S];
+  for (unsigned u = 0; u < Values.size(); u++) {
+    if (Values[u].first == L)
+      return Values[u].second;
+  }
+  Values.push_back(std::make_pair(L, LoopVariant));
   LoopDisposition D = computeLoopDisposition(S, L);
-  return LoopDispositions[S][L] = D;
+  SmallVector<std::pair<const Loop *, LoopDisposition>, 2> &Values2 = LoopDispositions[S];
+  for (unsigned u = Values2.size(); u > 0; u--) {
+    if (Values2[u - 1].first == L) {
+      Values2[u - 1].second = D;
+      break;
+    }
+  }
+  return D;
 }
 
 ScalarEvolution::LoopDisposition
@@ -6964,14 +6977,21 @@ bool ScalarEvolution::hasComputableLoopEvolution(const SCEV *S, const Loop *L) {
 
 ScalarEvolution::BlockDisposition
 ScalarEvolution::getBlockDisposition(const SCEV *S, const BasicBlock *BB) {
-  std::map<const BasicBlock *, BlockDisposition> &Values = BlockDispositions[S];
-  std::pair<std::map<const BasicBlock *, BlockDisposition>::iterator, bool>
-    Pair = Values.insert(std::make_pair(BB, DoesNotDominateBlock));
-  if (!Pair.second)
-    return Pair.first->second;
-
+  SmallVector<std::pair<const BasicBlock *, BlockDisposition>, 2> &Values = BlockDispositions[S];
+  for (unsigned u = 0; u < Values.size(); u++) {
+    if (Values[u].first == BB)
+      return Values[u].second;
+  }
+  Values.push_back(std::make_pair(BB, DoesNotDominateBlock));
   BlockDisposition D = computeBlockDisposition(S, BB);
-  return BlockDispositions[S][BB] = D;
+  SmallVector<std::pair<const BasicBlock *, BlockDisposition>, 2> &Values2 = BlockDispositions[S];
+  for (unsigned u = Values2.size(); u > 0; u--) {
+    if (Values2[u - 1].first == BB) {
+      Values2[u - 1].second = D;
+      break;
+    }
+  }
+  return D;
 }
 
 ScalarEvolution::BlockDisposition