Allow -1 to assign max value to unsigned bitfields.

Silence the -Wbitfield-constant-conversion warning for when -1 or other
negative values are assigned to unsigned bitfields, provided that the bitfield
is wider than the minimum number of bits needed to encode the negative value.

llvm-svn: 277796

2 files changed, 13 insertions, 1 deletions

diff --git a/clang/test/Sema/bitfield.c b/clang/test/Sema/bitfield.c
index 810dc798eaa..d625366e4e1 100644
--- a/clang/test/Sema/bitfield.c
+++ b/clang/test/Sema/bitfield.c
@@ -64,7 +64,7 @@ typedef signed Signed;
 
 struct Test5 { unsigned n : 2; } t5;
 // Bitfield is unsigned
-struct Test5 sometest5 = {-1}; // expected-warning {{implicit truncation from 'int' to bitfield changes value from -1 to 3}}
+struct Test5 sometest5 = {-1};
 typedef __typeof__(+t5.n) Signed;  // ... but promotes to signed.
 
 typedef __typeof__(t5.n + 0) Signed; // Arithmetic promotes.
diff --git a/clang/test/Sema/constant-conversion.c b/clang/test/Sema/constant-conversion.c
index b717f932533..203e7373897 100644
--- a/clang/test/Sema/constant-conversion.c
+++ b/clang/test/Sema/constant-conversion.c
@@ -113,3 +113,15 @@ void test9() {
 
   char array_init[] = { 255, 127, 128, 129, 0 };
 }
+
+void test10() {
+  struct S {
+    unsigned a : 4;
+  } s;
+  s.a = -1;
+  s.a = 15;
+  s.a = -8;
+
+  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}}
+}