Index: lib/Analysis/LazyValueInfo.cpp
===================================================================
--- lib/Analysis/LazyValueInfo.cpp
+++ lib/Analysis/LazyValueInfo.cpp
@@ -27,6 +27,7 @@
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/IR/ValueHandle.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetLibraryInfo.h"
@@ -37,6 +38,12 @@
 
 #define DEBUG_TYPE "lazy-value-info"
 
+// This threshold is purticularly tuned with some special cases exposing
+// regression of compile time and memory consumption.
+static cl::opt<unsigned>
+OverdefinedThreshold("lvi-overdefined-threshold", cl::init(1500), cl::Hidden,
+    cl::desc("Threshold of lowering lattice value 'overdefined'."));
+
 char LazyValueInfo::ID = 0;
 INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
                 "Lazy Value Information Analysis", false, true)
@@ -348,6 +355,9 @@
     const DataLayout *DL;
     /// An optional DT pointer.
     DominatorTree *DT;
+    /// A counter to record how many times Overdefined has been tried to be
+    /// lowered.
+    unsigned LoweringOverdefinedTimes;
     
     friend struct LVIValueHandle;
     
@@ -480,6 +490,7 @@
 }
 
 void LazyValueInfoCache::solve() {
+  LoweringOverdefinedTimes = 0;
   while (!BlockValueStack.empty()) {
     std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
     if (solveBlockValue(e.second, e.first)) {
@@ -539,8 +550,14 @@
   // BB2. So we should have to follow data flow propagation algorithm to get the
   // value on edge BB1->BB2 propagated to BB2, and finally %v on BB2 has a
   // constant range describing a negative value.
+  //
+  // However, this further computing could increase both time and space
+  // complexity. Therefore, we introduce OverdefinedThreshold to control
+  // the maximum times of further lowering lattice value 'overdefined'.
 
-  if (!BBLV.isUndefined() && !BBLV.isOverdefined()) {
+  if ((!BBLV.isUndefined() && !BBLV.isOverdefined()) ||
+      (BBLV.isOverdefined() &&
+       (LoweringOverdefinedTimes > OverdefinedThreshold))) {
     DEBUG(dbgs() << "  reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
     
     // Since we're reusing a cached value here, we don't need to update the 
@@ -554,6 +571,7 @@
   // lattice value to overdefined, so that cycles will terminate and be
   // conservatively correct.
   BBLV.markOverdefined();
+  LoweringOverdefinedTimes++;
   
   Instruction *BBI = dyn_cast<Instruction>(Val);
   if (!BBI || BBI->getParent() != BB) {