r343560 - Added warning for unary minus used with unsigned type

[David Bolvansky via cfe-commits]

Author: xbolva00
Date: Mon Oct  1 23:02:30 2018
New Revision: 343560

URL: http://llvm.org/viewvc/llvm-project?rev=343560&view=rev
Log:
Added warning for unary minus used with unsigned type

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

Fixes PR38950

Reviewers: rsmith, craig.topper, spatel, RKSimon, aaron.ballman, thakis

Reviewed By: rsmith

Subscribers: joerg, Quuxplusone, lebedev.ri, craig.topper, RKSimon, cfe-commits

Differential Revision: https://reviews.llvm.org/D52137

Added:
    cfe/trunk/test/Sema/unary-minus-integer-impcast.c
Modified:
    cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
    cfe/trunk/lib/Sema/SemaChecking.cpp

Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=343560&r1=343559&r2=343560&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Mon Oct  1 23:02:30 2018
@@ -3197,6 +3197,12 @@ def warn_impcast_integer_sign_conditiona
 def warn_impcast_integer_precision : Warning<
   "implicit conversion loses integer precision: %0 to %1">,
   InGroup<Conversion>, DefaultIgnore;
+def warn_impcast_high_order_zero_bits : Warning<
+  "higher order bits are zeroes after implicit conversion">,
+  InGroup<Conversion>, DefaultIgnore;
+def warn_impcast_nonnegative_result : Warning<
+  "the resulting value is always non-negative after implicit conversion">,
+  InGroup<SignConversion>, DefaultIgnore;
 def warn_impcast_integer_64_32 : Warning<
   "implicit conversion loses integer precision: %0 to %1">,
   InGroup<Shorten64To32>, DefaultIgnore;

Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=343560&r1=343559&r2=343560&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
+++ cfe/trunk/lib/Sema/SemaChecking.cpp Mon Oct  1 23:02:30 2018
@@ -10896,6 +10896,19 @@ CheckImplicitConversion(Sema &S, Expr *E
     return DiagnoseImpCast(S, E, T, CC, diag::warn_impcast_integer_precision);
   }
 
+  if (TargetRange.Width > SourceRange.Width) {
+    if (auto *UO = dyn_cast<UnaryOperator>(E))
+      if (UO->getOpcode() == UO_Minus)
+        if (Source->isUnsignedIntegerType()) {
+          if (Target->isUnsignedIntegerType())
+            return DiagnoseImpCast(S, E, T, CC,
+                                   diag::warn_impcast_high_order_zero_bits);
+          if (Target->isSignedIntegerType())
+            return DiagnoseImpCast(S, E, T, CC,
+                                   diag::warn_impcast_nonnegative_result);
+        }
+  }
+
   if (TargetRange.Width == SourceRange.Width && !TargetRange.NonNegative &&
       SourceRange.NonNegative && Source->isSignedIntegerType()) {
     // Warn when doing a signed to signed conversion, warn if the positive

Added: cfe/trunk/test/Sema/unary-minus-integer-impcast.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/unary-minus-integer-impcast.c?rev=343560&view=auto
==============================================================================
--- cfe/trunk/test/Sema/unary-minus-integer-impcast.c (added)
+++ cfe/trunk/test/Sema/unary-minus-integer-impcast.c Mon Oct  1 23:02:30 2018
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 %s -verify -Wconversion -fsyntax-only -triple x86_64-pc-linux-gnu
+// RUN: %clang_cc1 %s -verify -Wconversion -fsyntax-only -triple i386-pc-linux-gnu
+
+void test(void) {
+  unsigned int a = 1;
+
+  unsigned long long b = -a; // expected-warning {{higher order bits are zeroes after implicit conversion}}
+  long long c = -a;          // expected-warning {{the resulting value is always non-negative after implicit conversion}}
+
+  unsigned long b2 = -a;
+#ifdef __x86_64__
+// expected-warning at -2 {{higher order bits are zeroes after implicit conversion}}
+#endif
+  long c2 = -a;
+#ifdef __x86_64__
+// expected-warning at -2 {{the resulting value is always non-negative after implicit conversion}}
+#else
+// expected-warning at -4 {{implicit conversion changes signedness: 'unsigned int' to 'long'}}
+#endif
+}