Author: jrose Date: Mon Oct 23 19:17:07 2017 New Revision: 316408 URL: http://llvm.org/viewvc/llvm-project?rev=316408&view=rev Log: Unnamed bitfields don't block constant evaluation of constexpr ctors
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. Modified: cfe/trunk/lib/AST/ExprConstant.cpp cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp cfe/trunk/test/SemaCXX/warn-global-constructors.cpp Modified: cfe/trunk/lib/AST/ExprConstant.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ExprConstant.cpp?rev=316408&r1=316407&r2=316408&view=diff ============================================================================== --- cfe/trunk/lib/AST/ExprConstant.cpp (original) +++ cfe/trunk/lib/AST/ExprConstant.cpp Mon Oct 23 19:17:07 2017 @@ -1818,6 +1818,9 @@ static bool CheckConstantExpression(Eval } } for (const auto *I : RD->fields()) { + if (I->isUnnamedBitfield()) + continue; + if (!CheckConstantExpression(Info, DiagLoc, I->getType(), Value.getStructField(I->getFieldIndex()))) return false; Modified: cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp?rev=316408&r1=316407&r2=316408&view=diff ============================================================================== --- cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp (original) +++ cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp Mon Oct 23 19:17:07 2017 @@ -1931,6 +1931,22 @@ namespace Bitfields { }; 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 { Modified: cfe/trunk/test/SemaCXX/warn-global-constructors.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/warn-global-constructors.cpp?rev=316408&r1=316407&r2=316408&view=diff ============================================================================== --- cfe/trunk/test/SemaCXX/warn-global-constructors.cpp (original) +++ cfe/trunk/test/SemaCXX/warn-global-constructors.cpp Mon Oct 23 19:17:07 2017 @@ -126,3 +126,22 @@ namespace pr20420 { 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}} +} _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
