BasicConstraintManager:

- Fix nonsensical logic in AssumeSymLE. When comparing 'sym <= constant' and the
  constant is the minimum integer value, add the constraint that 'sym ==
  constant' when the path is deemed feasible.  All other cases are feasible.
- Improve AssumeSymLT to address <rdar://problem/6407949>.  When comparing
  'sym < constant' and constant is the minimum integer value we know the
  path is infeasible.
- Add test case for <rdar://problem/6407949>.

llvm-svn: 60489

clang/lib/Analysis/BasicConstraintManager.cpp

@@ -312,6 +312,13 @@ BasicConstraintManager::AssumeSymEQ(const GRState* St, SymbolID sym,
 const GRState*
 BasicConstraintManager::AssumeSymLT(const GRState* St, SymbolID sym,
                                     const llvm::APSInt& V, bool& isFeasible) {
+  
+  // Is 'V' the smallest possible value?
+  if (V == llvm::APSInt::getMinValue(V.getBitWidth(), V.isSigned())) {
+    // sym cannot be any value less than 'V'.  This path is infeasible.
+    isFeasible = false;
+    return St;
+  }
 
   // FIXME: For now have assuming x < y be the same as assuming sym != V;
   return AssumeSymNE(St, sym, V, isFeasible);
@@ -345,17 +352,28 @@ const GRState*
 BasicConstraintManager::AssumeSymLE(const GRState* St, SymbolID sym,
                                     const llvm::APSInt& V, bool& isFeasible) {
 
-  // FIXME: Primitive logic for now.  Only reject a path if the value of
-  //  sym is a constant X and !(X <= V).
-
+  // Reject a path if the value of sym is a constant X and !(X <= V).
   if (const llvm::APSInt* X = getSymVal(St, sym)) {
     isFeasible = *X <= V;
     return St;
   }
   
-  isFeasible = !isNotEqual(St, sym, V) || 
-               (V != llvm::APSInt::getMinValue(V.getBitWidth(), V.isSigned()));
-  
+  // Sym is not a constant, but it is worth looking to see if V is the
+  // minimum integer value.
+  if (V == llvm::APSInt::getMinValue(V.getBitWidth(), V.isSigned())) {
+    // If we know that sym != V, then this condition is infeasible since
+    // there is no other value less than V.    
+    isFeasible = !isNotEqual(St, sym, V);
+    
+    // If the path is still feasible then as a consequence we know that
+    // 'sym == V' because we cannot have 'sym < V' (no smaller values).
+    // Add this constraint.
+    if (isFeasible)
+      return AddEQ(St, sym, V);
+  }
+  else
+    isFeasible = true;
+    
   return St;
 }
 

clang/test/Analysis/null-deref-ps.c

@@ -134,3 +134,13 @@ int* f10(int* p, signed char x, int y) {
   return p;
 }
 
+// Test case from <rdar://problem/6407949>
+void f11(unsigned i) {
+  int *x = 0;
+  if (i >= 0) {
+    // always true
+  } else {
+    *x = 42; // no-warning
+  }
+}
+