[clang] ac3edc5 - [analyzer][solver] Handle simplification to ConcreteInt

[Gabor Marton via cfe-commits]

Author: Gabor Marton
Date: 2021-10-14T17:53:29+02:00
New Revision: ac3edc5af09947210d8f8d25ddd7e42379ef6454

URL: https://github.com/llvm/llvm-project/commit/ac3edc5af09947210d8f8d25ddd7e42379ef6454
DIFF: https://github.com/llvm/llvm-project/commit/ac3edc5af09947210d8f8d25ddd7e42379ef6454.diff

LOG: [analyzer][solver] Handle simplification to ConcreteInt

The solver's symbol simplification mechanism was not able to handle cases
when a symbol is simplified to a concrete integer. This patch adds the
capability.

E.g., in the attached lit test case, the original symbol is `c + 1` and
it has a `[0, 0]` range associated with it. Then, a new condition `c == 0`
is assumed, so a new range constraint `[0, 0]` comes in for `c` and
simplification kicks in. `c + 1` becomes `0 + 1`, but the associated
range is `[0, 0]`, so now we are able to realize the contradiction.

Differential Revision: https://reviews.llvm.org/D110913

Added: 
    clang/test/Analysis/solver-sym-simplification-concreteint.c

Modified: 
    clang/include/clang/StaticAnalyzer/Core/PathSensitive/RangedConstraintManager.h
    clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
    clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/StaticAnalyzer/Core/PathSensitive/RangedConstraintManager.h b/clang/include/clang/StaticAnalyzer/Core/PathSensitive/RangedConstraintManager.h
index c1d2b4665f1d3..599e4ec812a1b 100644
--- a/clang/include/clang/StaticAnalyzer/Core/PathSensitive/RangedConstraintManager.h
+++ b/clang/include/clang/StaticAnalyzer/Core/PathSensitive/RangedConstraintManager.h
@@ -389,11 +389,22 @@ class RangedConstraintManager : public SimpleConstraintManager {
   static void computeAdjustment(SymbolRef &Sym, llvm::APSInt &Adjustment);
 };
 
-/// Try to simplify a given symbolic expression's associated value based on the
-/// constraints in State. This is needed because the Environment bindings are
-/// not getting updated when a new constraint is added to the State.
+/// Try to simplify a given symbolic expression based on the constraints in
+/// State. This is needed because the Environment bindings are not getting
+/// updated when a new constraint is added to the State. If the symbol is
+/// simplified to a non-symbol (e.g. to a constant) then the original symbol
+/// is returned. We use this function in the family of assumeSymNE/EQ/LT/../GE
+/// functions where we can work only with symbols. Use the other function
+/// (simplifyToSVal) if you are interested in a simplification that may yield
+/// a concrete constant value.
 SymbolRef simplify(ProgramStateRef State, SymbolRef Sym);
 
+/// Try to simplify a given symbolic expression's associated `SVal` based on the
+/// constraints in State. This is very similar to `simplify`, but this function
+/// always returns the simplified SVal. The simplified SVal might be a single
+/// constant (i.e. `ConcreteInt`).
+SVal simplifyToSVal(ProgramStateRef State, SymbolRef Sym);
+
 } // namespace ento
 } // namespace clang
 

diff  --git a/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp b/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
index 8299486938850..d1113569c59db 100644
--- a/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
+++ b/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
@@ -2106,7 +2106,20 @@ EquivalenceClass::simplify(SValBuilder &SVB, RangeSet::Factory &F,
                            ProgramStateRef State, EquivalenceClass Class) {
   SymbolSet ClassMembers = Class.getClassMembers(State);
   for (const SymbolRef &MemberSym : ClassMembers) {
-    SymbolRef SimplifiedMemberSym = ento::simplify(State, MemberSym);
+
+    const SVal SimplifiedMemberVal = simplifyToSVal(State, MemberSym);
+    const SymbolRef SimplifiedMemberSym = SimplifiedMemberVal.getAsSymbol();
+
+    // The symbol is collapsed to a constant, check if the current State is
+    // still feasible.
+    if (const auto CI = SimplifiedMemberVal.getAs<nonloc::ConcreteInt>()) {
+      const llvm::APSInt &SV = CI->getValue();
+      const RangeSet *ClassConstraint = getConstraint(State, Class);
+      // We have found a contradiction.
+      if (ClassConstraint && !ClassConstraint->contains(SV))
+        return nullptr;
+    }
+
     if (SimplifiedMemberSym && MemberSym != SimplifiedMemberSym) {
       // The simplified symbol should be the member of the original Class,
       // however, it might be in another existing class at the moment. We

diff  --git a/clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp b/clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp
index d227c025fb203..80f3054a5a37f 100644
--- a/clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp
+++ b/clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp
@@ -226,9 +226,13 @@ void RangedConstraintManager::computeAdjustment(SymbolRef &Sym,
   }
 }
 
-SymbolRef simplify(ProgramStateRef State, SymbolRef Sym) {
+SVal simplifyToSVal(ProgramStateRef State, SymbolRef Sym) {
   SValBuilder &SVB = State->getStateManager().getSValBuilder();
-  SVal SimplifiedVal = SVB.simplifySVal(State, SVB.makeSymbolVal(Sym));
+  return SVB.simplifySVal(State, SVB.makeSymbolVal(Sym));
+}
+
+SymbolRef simplify(ProgramStateRef State, SymbolRef Sym) {
+  SVal SimplifiedVal = simplifyToSVal(State, Sym);
   if (SymbolRef SimplifiedSym = SimplifiedVal.getAsSymbol())
     return SimplifiedSym;
   return Sym;

diff  --git a/clang/test/Analysis/solver-sym-simplification-concreteint.c b/clang/test/Analysis/solver-sym-simplification-concreteint.c
new file mode 100644
index 0000000000000..bfd25eb4f59e5
--- /dev/null
+++ b/clang/test/Analysis/solver-sym-simplification-concreteint.c
@@ -0,0 +1,40 @@
+// RUN: %clang_analyze_cc1 %s \
+// RUN:   -analyzer-checker=core \
+// RUN:   -analyzer-checker=debug.ExprInspection \
+// RUN:   -analyzer-config eagerly-assume=false \
+// RUN:   -verify
+
+void clang_analyzer_warnIfReached();
+void clang_analyzer_eval();
+
+void test_simplification_to_concrete_int_infeasible(int b, int c) {
+  if (c + b != 0)     // c + b == 0
+    return;
+  if (b != 1)         // b == 1  --> c + 1 == 0
+    return;
+  if (c != 1)         // c == 1  --> 1 + 1 == 0 contradiction
+    return;
+  clang_analyzer_warnIfReached(); // no-warning
+
+  // Keep the symbols and the constraints! alive.
+  (void)(b * c);
+  return;
+}
+
+void test_simplification_to_concrete_int_feasible(int b, int c) {
+  if (c + b != 0)
+    return;
+                      // c + b == 0
+  if (b != 1)
+    return;
+                      // b == 1   -->  c + 1 == 0
+  if (c != -1)
+    return;
+                      // c == -1  --> -1 + 1 == 0 OK
+  clang_analyzer_warnIfReached(); // expected-warning{{REACHABLE}}
+  clang_analyzer_eval(c == -1);   // expected-warning{{TRUE}}
+
+  // Keep the symbols and the constraints! alive.
+  (void)(b * c);
+  return;
+}