From 71bb9879974ae39d1a8fc0d349c00049571a72d2 Mon Sep 17 00:00:00 2001
From: Pavel Labath <labath@google.com>
Date: Mon, 19 Aug 2013 15:23:34 +0000
Subject: [PATCH] [analyzer] Fix inefficiency in dead symbol removal

Summary:
ScanReachableSymbols uses a "visited" set to avoid scanning the same object
twice. However, it did not use the optimization for LazyCompoundVal objects,
which resulted in exponential complexity for long chains of temporary objects.
Adding this resulted in a decrease of analysis time from >3h to 3 seconds for
some files.

Reviewers: jordan_rose

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1398

llvm-svn: 188677
---
 .../Core/PathSensitive/ProgramState.h         |  3 +-
 .../lib/StaticAnalyzer/Core/ProgramState.cpp  | 36 ++++++++++---------
 2 files changed, 21 insertions(+), 18 deletions(-)

diff --git a/clang/include/clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h b/clang/include/clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h
index ed1ab8c4cb45..96f62423393d 100644
--- a/clang/include/clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h
+++ b/clang/include/clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h
@@ -798,7 +798,7 @@ CB ProgramState::scanReachableSymbols(const MemRegion * const *beg,
 /// A Utility class that allows to visit the reachable symbols using a custom
 /// SymbolVisitor.
 class ScanReachableSymbols {
-  typedef llvm::DenseMap<const void*, unsigned> VisitedItems;
+  typedef llvm::DenseSet<const void*> VisitedItems;
 
   VisitedItems visited;
   ProgramStateRef state;
@@ -808,6 +808,7 @@ public:
   ScanReachableSymbols(ProgramStateRef st, SymbolVisitor& v)
     : state(st), visitor(v) {}
 
+  bool scan(nonloc::LazyCompoundVal val);
   bool scan(nonloc::CompoundVal val);
   bool scan(SVal val);
   bool scan(const MemRegion *R);
diff --git a/clang/lib/StaticAnalyzer/Core/ProgramState.cpp b/clang/lib/StaticAnalyzer/Core/ProgramState.cpp
index 653b69bf4860..fbd3fc526d3b 100644
--- a/clang/lib/StaticAnalyzer/Core/ProgramState.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ProgramState.cpp
@@ -526,6 +526,19 @@ ProgramStateRef ProgramStateManager::removeGDM(ProgramStateRef state, void *Key)
   return getPersistentState(NewState);
 }
 
+bool ScanReachableSymbols::scan(nonloc::LazyCompoundVal val) {
+  bool wasVisited = !visited.insert(val.getCVData()).second;
+  if (wasVisited)
+    return true;
+
+  StoreManager &StoreMgr = state->getStateManager().getStoreManager();
+  // FIXME: We don't really want to use getBaseRegion() here because pointer
+  // arithmetic doesn't apply, but scanReachableSymbols only accepts base
+  // regions right now.
+  const MemRegion *R = val.getRegion()->getBaseRegion();
+  return StoreMgr.scanReachableSymbols(val.getStore(), R, *this);
+}
+
 bool ScanReachableSymbols::scan(nonloc::CompoundVal val) {
   for (nonloc::CompoundVal::iterator I=val.begin(), E=val.end(); I!=E; ++I)
     if (!scan(*I))
@@ -535,10 +548,9 @@ bool ScanReachableSymbols::scan(nonloc::CompoundVal val) {
 }
 
 bool ScanReachableSymbols::scan(const SymExpr *sym) {
-  unsigned &isVisited = visited[sym];
-  if (isVisited)
+  bool wasVisited = !visited.insert(sym).second;
+  if (wasVisited)
     return true;
-  isVisited = 1;
   
   if (!visitor.VisitSymbol(sym))
     return false;
@@ -570,16 +582,8 @@ bool ScanReachableSymbols::scan(SVal val) {
     return scan(X->getRegion());
 
   if (Optional<nonloc::LazyCompoundVal> X =
-          val.getAs<nonloc::LazyCompoundVal>()) {
-    StoreManager &StoreMgr = state->getStateManager().getStoreManager();
-    // FIXME: We don't really want to use getBaseRegion() here because pointer
-    // arithmetic doesn't apply, but scanReachableSymbols only accepts base
-    // regions right now.
-    if (!StoreMgr.scanReachableSymbols(X->getStore(),
-                                       X->getRegion()->getBaseRegion(),
-                                       *this))
-      return false;
-  }
+          val.getAs<nonloc::LazyCompoundVal>())
+    return scan(*X);
 
   if (Optional<nonloc::LocAsInteger> X = val.getAs<nonloc::LocAsInteger>())
     return scan(X->getLoc());
@@ -600,11 +604,9 @@ bool ScanReachableSymbols::scan(const MemRegion *R) {
   if (isa<MemSpaceRegion>(R))
     return true;
   
-  unsigned &isVisited = visited[R];
-  if (isVisited)
+  bool wasVisited = !visited.insert(R).second;
+  if (wasVisited)
     return true;
-  isVisited = 1;
-  
   
   if (!visitor.VisitMemRegion(R))
     return false;