Unnamed bitfields don't block constant evaluation of constexpr ctors (#136)
C++14 [dcl.constexpr]p4 states that in the body of a constexpr
constructor,
> every non-variant non-static data member and base class sub-object
shall be initialized
However, [class.bit]p2 notes that
> Unnamed bit-fields are not members and cannot be initialized.
Therefore, we should make sure to filter them out of the check that
all fields are initialized.
Fixing this makes the constant evaluator a bit smarter, and
specifically allows constexpr constructors to avoid tripping
-Wglobal-constructors when the type contains unnamed bitfields.
Reviewed at https://reviews.llvm.org/D39035.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@316408 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index a26b608..419e9a7 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -1758,6 +1758,9 @@
}
}
for (const auto *I : RD->fields()) {
+ if (I->isUnnamedBitfield())
+ continue;
+
if (!CheckConstantExpression(Info, DiagLoc, I->getType(),
Value.getStructField(I->getFieldIndex())))
return false;
diff --git a/test/SemaCXX/constant-expression-cxx11.cpp b/test/SemaCXX/constant-expression-cxx11.cpp
index 3fda2d0..c834da7 100644
--- a/test/SemaCXX/constant-expression-cxx11.cpp
+++ b/test/SemaCXX/constant-expression-cxx11.cpp
@@ -1904,6 +1904,22 @@
};
static_assert(X::f(3) == -1, "3 should truncate to -1");
}
+
+ struct HasUnnamedBitfield {
+ unsigned a;
+ unsigned : 20;
+ unsigned b;
+
+ constexpr HasUnnamedBitfield() : a(), b() {}
+ constexpr HasUnnamedBitfield(unsigned a, unsigned b) : a(a), b(b) {}
+ };
+
+ void testUnnamedBitfield() {
+ const HasUnnamedBitfield zero{};
+ int a = 1 / zero.b; // expected-warning {{division by zero is undefined}}
+ const HasUnnamedBitfield oneZero{1, 0};
+ int b = 1 / oneZero.b; // expected-warning {{division by zero is undefined}}
+ }
}
namespace ZeroSizeTypes {
diff --git a/test/SemaCXX/warn-global-constructors.cpp b/test/SemaCXX/warn-global-constructors.cpp
index 8568264..430f239 100644
--- a/test/SemaCXX/warn-global-constructors.cpp
+++ b/test/SemaCXX/warn-global-constructors.cpp
@@ -126,3 +126,22 @@
void *array_storage[1];
const int &global_reference = *(int *)array_storage;
}
+
+namespace bitfields {
+ struct HasUnnamedBitfield {
+ unsigned a;
+ unsigned : 20;
+ unsigned b;
+
+ constexpr HasUnnamedBitfield() : a(), b() {}
+ constexpr HasUnnamedBitfield(unsigned a, unsigned b) : a(a), b(b) {}
+ explicit HasUnnamedBitfield(unsigned a) {}
+ };
+
+ const HasUnnamedBitfield zeroConst{};
+ HasUnnamedBitfield zeroMutable{};
+ const HasUnnamedBitfield explicitConst{1, 2};
+ HasUnnamedBitfield explicitMutable{1, 2};
+ const HasUnnamedBitfield nonConstexprConst{1}; // expected-warning {{global constructor}}
+ HasUnnamedBitfield nonConstexprMutable{1}; // expected-warning {{global constructor}}
+}
