[PATCH] D52137: Added warning for unary minus used with unsigned type

[Dávid Bolvanský via Phabricator via cfe-commits]

xbolva00 created this revision.
xbolva00 added a reviewer: rsmith.
Herald added a subscriber: cfe-commits.

Inspired by MSVC, which found some occurrences of this expression on our code base.

Fixes PR38950


Repository:
  rC Clang

https://reviews.llvm.org/D52137

Files:
  include/clang/Basic/DiagnosticSemaKinds.td
  lib/Sema/SemaExpr.cpp
  test/Sema/unary-minus-unsigned.c


Index: test/Sema/unary-minus-unsigned.c
===================================================================
--- test/Sema/unary-minus-unsigned.c
+++ test/Sema/unary-minus-unsigned.c
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 %s -verify -pedantic -fsyntax-only
+
+void test1(void) {
+    unsigned int a = 1;
+    unsigned long b = 2;
+    unsigned long long c = 1;
+ 
+    unsigned int a2 = -a; // expected-error {{unary minus operator applied to type 'unsigned int', result value is still positive}}
+    unsigned long b2 = -b; // expected-error {{unary minus operator applied to type 'unsigned long', result value is still positive}}
+    unsigned long long c2 = -c; // expected-error {{unary minus operator applied to type 'unsigned long long', result value is still positive}}
+ }
Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -12646,8 +12646,12 @@
     resultType = Input.get()->getType();
     if (resultType->isDependentType())
       break;
-    if (resultType->isArithmeticType()) // C99 6.5.3.3p1
+    if (resultType->isArithmeticType()) { // C99 6.5.3.3p1
+      if (Opc == UO_Minus && resultType->isUnsignedIntegerType())
+        return ExprError(Diag(OpLoc, diag::err_unsignedtypecheck_unary_minus)
+                         << resultType << Input.get()->getSourceRange());
       break;
+    }
     else if (resultType->isVectorType() &&
              // The z vector extensions don't allow + or - with bool vectors.
              (!Context.getLangOpts().ZVector ||
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -5820,6 +5820,8 @@
   "taking the address of a destructor">;
 def err_typecheck_unary_expr : Error<
   "invalid argument type %0 to unary expression">;
+def err_unsignedtypecheck_unary_minus : Error<
+  "unary minus operator applied to type %0, result value is still positive">;
 def err_typecheck_indirection_requires_pointer : Error<
   "indirection requires pointer operand (%0 invalid)">;
 def ext_typecheck_indirection_through_void_pointer : ExtWarn<


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