[clang] [sema] Improve -Wsign-compare (PR #65684)

[Shafik Yaghmour via cfe-commits]

================
@@ -14043,28 +14039,61 @@ static bool CheckTautologicalComparison(Sema &S, BinaryOperator *E,
   return true;
 }
 
+namespace {
+struct AnalyzeImplicitConversionsWorkItem {
+  Expr *E;
+  SourceLocation CC;
+  unsigned IsListInit : 1;
+  unsigned IsTopLevelExpr : 1;
+};
+
+class ImplicitConversionChecker {
+  Sema &S;
+  Expr *TopLevelExpr;
+
+  void AnalyzeCompoundAssignment(BinaryOperator *E);
+  void AnalyzeImplicitConversions(
+      AnalyzeImplicitConversionsWorkItem Item,
+      llvm::SmallVectorImpl<AnalyzeImplicitConversionsWorkItem> &WorkList);
+  void AnalyzeImpConvsInComparison(BinaryOperator *E);
+  void AnalyzeComparison(BinaryOperator *E);
+  void AnalyzeAssignment(BinaryOperator *E);
+  void CheckConditionalOperand(Expr *E, QualType T, SourceLocation CC,
+                               bool &ICContext);
+  void CheckConditionalOperator(AbstractConditionalOperator *E,
+                                SourceLocation CC, QualType T);
+
+public:
+  ImplicitConversionChecker(Sema &S) : S(S), TopLevelExpr(nullptr) {}
+
+  void AnalyzeImplicitConversions(Expr *E, SourceLocation CC,
+                                  bool IsInitList = false,
+                                  bool IsTopLevelExpr = false);
+};
+} // namespace
+
 /// Analyze the operands of the given comparison.  Implements the
 /// fallback case from AnalyzeComparison.
-static void AnalyzeImpConvsInComparison(Sema &S, BinaryOperator *E) {
-  AnalyzeImplicitConversions(S, E->getLHS(), E->getOperatorLoc());
-  AnalyzeImplicitConversions(S, E->getRHS(), E->getOperatorLoc());
+void ImplicitConversionChecker::AnalyzeImpConvsInComparison(BinaryOperator *E) {
+  AnalyzeImplicitConversions(E->getLHS(), E->getOperatorLoc(), false, false);
+  AnalyzeImplicitConversions(E->getRHS(), E->getOperatorLoc(), false, false);
----------------
shafik wrote:

```suggestion
  AnalyzeImplicitConversions(E->getLHS(), E->getOperatorLoc(), /*IsInitList=*/false, /*IsTopLevelExpr=*/false);
  AnalyzeImplicitConversions(E->getRHS(), E->getOperatorLoc(), /*IsInitList=*/false, /*IsTopLevelExpr=*/false);
```

https://github.com/llvm/llvm-project/pull/65684