[analyzer] SValBuilder::evalBinOpLN: try simplifying the RHS first (llvm#161537)

The first thing `SValBuilder::evalBinOpNN` does is simplify both
operators
([here](https://github.com/llvm/llvm-project/blob/main/clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp#L430-L437)),
why wouldn't we simplify the RHS in `SValBuilder::evalBinOpLN`?

When the LHS is an `Element`, the right side is simplified incidentally
when calling `evalBinOpNN`
([here](https://github.com/llvm/llvm-project/blob/main/clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp#L1169-L1170)).

Without this patch, the “base_complex” test case is **UNKNOWN** instead of **TRUE**.

Author: guillem-bartrina-sonarsource

clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp

@@ -1111,6 +1111,10 @@ SVal SimpleSValBuilder::evalBinOpLN(ProgramStateRef state,
   assert(!BinaryOperator::isComparisonOp(op) &&
          "arguments to comparison ops must be of the same type");
 
+  SVal simplifiedRhs = simplifySVal(state, rhs);
+  if (auto simplifiedRhsAsNonLoc = simplifiedRhs.getAs<NonLoc>())
+    rhs = *simplifiedRhsAsNonLoc;
+
   // Special case: rhs is a zero constant.
   if (rhs.isZeroConstant())
     return lhs;

clang/test/Analysis/loc-folding.cpp

@@ -0,0 +1,61 @@
+// RUN: %clang_analyze_cc1 -verify %s -analyzer-config eagerly-assume=false \
+// RUN:   -analyzer-checker=core,debug.ExprInspection
+
+void clang_analyzer_eval(bool);
+
+void element_constant() {
+  char arr[10];
+  clang_analyzer_eval(arr + 1 > arr); // expected-warning{{TRUE}}
+}
+
+void element_known() {
+  char arr[10];
+  int off = 1;
+  clang_analyzer_eval(arr + off > arr); // expected-warning{{TRUE}}
+}
+
+void element_constrained(int off) {
+  char arr[10];
+  if (off == 1) {
+    clang_analyzer_eval(arr + off > arr); // expected-warning{{TRUE}}
+  }
+}
+
+void element_unknown(int off) {
+  char arr[10];
+  clang_analyzer_eval(arr + off > arr); // expected-warning{{UNKNOWN}}
+}
+
+void element_complex(int off) {
+  char arr[10];
+  int comp = off * 2;
+  if (off == 1) {
+    clang_analyzer_eval(arr + comp); // expected-warning{{TRUE}}
+  }
+}
+
+void base_constant(int *arr) {
+  clang_analyzer_eval(arr + 1 > arr); // expected-warning{{TRUE}}
+}
+
+void base_known(int *arr) {
+  int off = 1;
+  clang_analyzer_eval(arr + off > arr); // expected-warning{{TRUE}}
+}
+
+void base_constrained(int *arr, int off) {
+  if (off == 1) {
+    clang_analyzer_eval(arr + off > arr); // expected-warning{{TRUE}}
+  }
+}
+
+void base_unknown(int *arr, int off) {
+  clang_analyzer_eval(arr + off > arr); // expected-warning{{UNKNOWN}}
+}
+
+void base_complex(int *arr, int off) {
+  int comp = off * 2;
+  if (off == 1) {
+    clang_analyzer_eval(arr + comp > arr); // expected-warning{{TRUE}}
+  }
+}