[analyzer][Solver] Teach SymbolicRangeInferrer about commutativity

This patch should not introduce much overhead as it only does one more
constraint map lookup, which is really quick.

Author: steakhal

clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp

@@ -1249,6 +1249,8 @@ class SymbolicRangeInferrer
         // calculate the effective range set by intersecting the range set
         // for A - B and the negated range set of B - A.
         getRangeForNegatedSymSym(SSE),
+        // If commutative, we may have constaints for the commuted variant.
+        getRangeCommutativeSymSym(SSE),
         // If Sym is a comparison expression (except <=>),
         // find any other comparisons with the same operands.
         // See function description.
@@ -1485,6 +1487,18 @@ class SymbolicRangeInferrer
         Sym->getType());
   }
 
+  std::optional<RangeSet> getRangeCommutativeSymSym(const SymSymExpr *SSE) {
+    bool IsCommutative = llvm::is_contained({BO_Add, BO_Mul}, SSE->getOpcode());
+    if (!IsCommutative)
+      return std::nullopt;
+
+    SymbolRef Commuted = State->getSymbolManager().getSymSymExpr(
+        SSE->getRHS(), BO_Add, SSE->getLHS(), SSE->getType());
+    if (const RangeSet *Range = getConstraint(State, Commuted))
+      return *Range;
+    return std::nullopt;
+  }
+
   // Returns ranges only for binary comparison operators (except <=>)
   // when left and right operands are symbolic values.
   // Finds any other comparisons with the same operands.

clang/test/Analysis/unary-sym-expr.c

@@ -33,8 +33,7 @@ void test_svalbuilder_simplification(int x, int y) {
   if (x + y != 3)
     return;
   clang_analyzer_eval(-(x + y) == -3); // expected-warning{{TRUE}}
-  // FIXME Commutativity is not supported yet.
-  clang_analyzer_eval(-(y + x) == -3); // expected-warning{{UNKNOWN}}
+  clang_analyzer_eval(-(y + x) == -3); // expected-warning{{TRUE}}
 }
 
 int test_fp(int flag) {