Fix Wbitfield-constant-conversion false positives

Summary:
The diagnostic did not handle ~ well. An expression such as ~0 is often used when 'all ones' is needed.

Differential Revision: https://reviews.llvm.org/D24232

llvm-svn: 282156

2 files changed, 11 insertions, 6 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 0604c5aeac4..119fe8c6d2a 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -8006,11 +8006,10 @@ bool AnalyzeBitFieldAssignment(Sema &S, FieldDecl *Bitfield, Expr *Init,
   unsigned OriginalWidth = Value.getBitWidth();
   unsigned FieldWidth = Bitfield->getBitWidthValue(S.Context);
 
-  if (Value.isSigned() && Value.isNegative())
+  if (!Value.isSigned() || Value.isNegative())
     if (UnaryOperator *UO = dyn_cast<UnaryOperator>(OriginalInit))
-      if (UO->getOpcode() == UO_Minus)
-        if (isa<IntegerLiteral>(UO->getSubExpr()))
-          OriginalWidth = Value.getMinSignedBits();
+      if (UO->getOpcode() == UO_Minus || UO->getOpcode() == UO_Not)
+        OriginalWidth = Value.getMinSignedBits();
 
   if (OriginalWidth <= FieldWidth)
     return false;
diff --git a/clang/test/Sema/constant-conversion.c b/clang/test/Sema/constant-conversion.c
index 203e7373897..b67c286f53a 100644
--- a/clang/test/Sema/constant-conversion.c
+++ b/clang/test/Sema/constant-conversion.c
@@ -69,7 +69,8 @@ void test7() {
 		unsigned int reserved:28;
 	} f;
 
-	f.twoBits1 = ~1; // expected-warning {{implicit truncation from 'int' to bitfield changes value from -2 to 2}}
+	f.twoBits1 = ~0; // no-warning
+	f.twoBits1 = ~1; // no-warning
 	f.twoBits2 = ~2; // expected-warning {{implicit truncation from 'int' to bitfield changes value from -3 to 1}}
 	f.twoBits1 &= ~1; // no-warning
 	f.twoBits2 &= ~2; // no-warning
@@ -114,6 +115,8 @@ void test9() {
   char array_init[] = { 255, 127, 128, 129, 0 };
 }
 
+#define A 1
+
 void test10() {
   struct S {
     unsigned a : 4;
@@ -121,7 +124,10 @@ void test10() {
   s.a = -1;
   s.a = 15;
   s.a = -8;
+  s.a = ~0;
+  s.a = ~0U;
+  s.a = ~(1<<A);
 
-  s.a = -9;  // expected-warning{{implicit truncation from 'int' to bitfield changes value from -9 to 7}}
+s.a = -9;  // expected-warning{{implicit truncation from 'int' to bitfield changes value from -9 to 7}}
   s.a = 16;  // expected-warning{{implicit truncation from 'int' to bitfield changes value from 16 to 0}}
 }