[Analyzer][Core] Simplify IntSym in SValBuilder

[martong]

Summary

Make the SimpleSValBuilder capable to simplify existing IntSym
expressions based on a newly added constraint on the sub-expression.

[steakhal]

Great stuff. Have you checked the coverage?

[martong]

In D113754#3127245, @steakhal wrote:

Great stuff. Have you checked the coverage?

Thanks for the review! So, here are the coverage results for the new test file:

1186           2 :     SVal VisitIntSymExpr(const IntSymExpr *S) {
1187           2 :       auto I = Cached.find(S);
1188           2 :       if (I != Cached.end())
1189           0 :         return I->second;
1190             :
1191           2 :       SVal RHS = Visit(S->getRHS());
1192           2 :       if (isUnchanged(S->getRHS(), RHS))
1193           0 :         return skip(S);
1194           2 :       SVal LHS = SVB.makeIntVal(S->getLHS());
1195             :       return cache(
1196           2 :           S, SVB.evalBinOp(State, S->getOpcode(), LHS, RHS, S->getType()));
1197             :     }

L1189 is not covered, but that is related to the caching mechanism, which is already existing and this patch is independent from that. We have the very same caching implementation in all the other Visit functions.
L1193 There is an existing test case in find-binop-constraints.cpp which covers this line. :

int test_lhs_and_rhs_further_constrained(int x, int y) {
  if (x % y != 1)
    return 0;
  if (x != 1)
    return 0;
  if (y != 2)
    return 0;
  clang_analyzer_eval(x % y == 1); // expected-warning{{TRUE}}
  clang_analyzer_eval(y == 2);     // expected-warning{{TRUE}}
  return 0;
}

I could have replicated this test case here, but hadn't been able to formulate any new expectations with a clang_analyzer_ function. So there is no visible functional change in this case with this patch concerning this line. Besides, all other existing Visit functions have the same optimization and they do an early return with skip if the symbol is unchanged.

[steakhal]

Great news, thanks.

clang/test/Analysis/svalbuilder-simplify-intsym.cpp

19

extra spaces?

clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp

SVal VisitSymIntExpr(const SymIntExpr *S) {
       } else {
         RHS = SVB.makeIntVal(S->getRHS());
       }
 
       return cache(
           S, SVB.evalBinOp(State, S->getOpcode(), LHS, RHS, S->getType()));
     }
 
+    SVal VisitIntSymExpr(const IntSymExpr *S) {
+      auto I = Cached.find(S);
+      if (I != Cached.end())
+        return I->second;
+
+      SVal RHS = Visit(S->getRHS());
+      if (isUnchanged(S->getRHS(), RHS))
+        return skip(S);
+      SVal LHS = SVB.makeIntVal(S->getLHS());
+      return cache(
+          S, SVB.evalBinOp(State, S->getOpcode(), LHS, RHS, S->getType()));
+    }
+
     SVal VisitSymSymExpr(const SymSymExpr *S) {
       auto I = Cached.find(S);
       if (I != Cached.end())
         return I->second;
 
       // For now don't try to simplify mixed Loc/NonLoc expressions
       // because they often appear from LocAsInteger operations
       // and we don't know how to combine a LocAsInteger

clang/test/Analysis/svalbuilder-simplify-intsym.cpp

+// RUN: %clang_analyze_cc1 %s \
+// RUN:   -analyzer-checker=core \
+// RUN:   -analyzer-checker=debug.ExprInspection \
+// RUN:   -analyzer-config eagerly-assume=false \
+// RUN:   -verify
+
+// Here we test whether the SValBuilder is capable to simplify existing
+// IntSym expressions based on a newly added constraint on the sub-expression.
+
+void clang_analyzer_eval(bool);
+
+void test_SValBuilder_simplifies_IntSym(int x, int y) {
+  // Most IntSym BinOps are transformed to SymInt in SimpleSValBuilder.
+  // Division is one exception.
+  x = 77 / y;
+  if (y != 1)
+    return;
+  clang_analyzer_eval(x == 77); // expected-warning{{TRUE}}
+  (void)(x * y);
+}