[Sema] Fix tautological bounds check warning with -fwrapv

clang/lib/Sema/SemaExpr.cpp

@@ -11789,10 +11789,11 @@ static bool checkForArray(const Expr *E) {
 /// Detect patterns ptr + size >= ptr and ptr + size < ptr, where ptr is a
 /// pointer and size is an unsigned integer. Return whether the result is
 /// always true/false.
-static std::optional<bool> isTautologicalBoundsCheck(const Expr *LHS,
+static std::optional<bool> isTautologicalBoundsCheck(Sema &S, const Expr *LHS,
                                                      const Expr *RHS,
                                                      BinaryOperatorKind Opc) {
-  if (!LHS->getType()->isPointerType())
+  if (!LHS->getType()->isPointerType() ||
+      S.getLangOpts().isSignedOverflowDefined())
     return std::nullopt;
 
   // Canonicalize to >= or < predicate.
@@ -11940,7 +11941,7 @@ static void diagnoseTautologicalComparison(Sema &S, SourceLocation Loc,
                                 << 1 /*array comparison*/
                                 << Result);
     } else if (std::optional<bool> Res =
-                   isTautologicalBoundsCheck(LHS, RHS, Opc)) {
+                   isTautologicalBoundsCheck(S, LHS, RHS, Opc)) {
       S.DiagRuntimeBehavior(Loc, nullptr,
                             S.PDiag(diag::warn_comparison_always)
                                 << 2 /*pointer comparison*/

clang/test/Sema/tautological-pointer-comparison.c

@@ -1,40 +1,72 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fsyntax-only -DFWRAPV -fwrapv -verify %s
+
+#ifdef FWRAPV
+// expected-no-diagnostics
+#endif
 
 int add_ptr_idx_ult_ptr(const char *ptr, unsigned index) {
-  return ptr + index < ptr; // expected-warning {{pointer comparison always evaluates to false}}
+#ifndef FWRAPV
+  // expected-warning@+2 {{pointer comparison always evaluates to false}}
+#endif
+  return ptr + index < ptr;
 }
 
 int add_idx_ptr_ult_ptr(const char *ptr, unsigned index) {
-  return index + ptr < ptr; // expected-warning {{pointer comparison always evaluates to false}}
+#ifndef FWRAPV
+  // expected-warning@+2 {{pointer comparison always evaluates to false}}
+#endif
+  return index + ptr < ptr;
 }
 
 int ptr_ugt_add_ptr_idx(const char *ptr, unsigned index) {
-  return ptr > ptr + index; // expected-warning {{pointer comparison always evaluates to false}}
+#ifndef FWRAPV
+  // expected-warning@+2 {{pointer comparison always evaluates to false}}
+#endif
+  return ptr > ptr + index;
 }
 
 int ptr_ugt_add_idx_ptr(const char *ptr, unsigned index) {
-  return ptr > index + ptr; // expected-warning {{pointer comparison always evaluates to false}}
+#ifndef FWRAPV
+  // expected-warning@+2 {{pointer comparison always evaluates to false}}
+#endif
+  return ptr > index + ptr;
 }
 
 int add_ptr_idx_uge_ptr(const char *ptr, unsigned index) {
-  return ptr + index >= ptr; // expected-warning {{pointer comparison always evaluates to true}}
+#ifndef FWRAPV
+  // expected-warning@+2 {{pointer comparison always evaluates to true}}
+#endif
+  return ptr + index >= ptr;
 }
 
 int add_idx_ptr_uge_ptr(const char *ptr, unsigned index) {
-  return index + ptr >= ptr; // expected-warning {{pointer comparison always evaluates to true}}
+#ifndef FWRAPV
+  // expected-warning@+2 {{pointer comparison always evaluates to true}}
+#endif
+  return index + ptr >= ptr;
 }
 
 int ptr_ule_add_ptr_idx(const char *ptr, unsigned index) {
-  return ptr <= ptr + index; // expected-warning {{pointer comparison always evaluates to true}}
+#ifndef FWRAPV
+  // expected-warning@+2 {{pointer comparison always evaluates to true}}
+#endif
+  return ptr <= ptr + index;
 }
 
 int ptr_ule_add_idx_ptr(const char *ptr, unsigned index) {
-  return ptr <= index + ptr; // expected-warning {{pointer comparison always evaluates to true}}
+#ifndef FWRAPV
+  // expected-warning@+2 {{pointer comparison always evaluates to true}}
+#endif
+  return ptr <= index + ptr;
 }
 
 int add_ptr_idx_ult_ptr_array(unsigned index) {
   char ptr[10];
-  return ptr + index < ptr; // expected-warning {{pointer comparison always evaluates to false}}
+#ifndef FWRAPV
+  // expected-warning@+2 {{pointer comparison always evaluates to false}}
+#endif
+  return ptr + index < ptr;
 }
 
 // Negative tests with wrong predicate.