diff options
author | David L. Jones <dlj@google.com> | 2017-01-09 21:38:07 +0000 |
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committer | David L. Jones <dlj@google.com> | 2017-01-09 21:38:07 +0000 |
commit | fb15aef140e7e832663b2c59cd50bb8958dee871 (patch) | |
tree | 7729bc0ec1a59c9cac2ff3b95e374a176166383f | |
parent | 266cb72185242313c85a9f33dc33944da8b2b403 (diff) |
Allow constexpr construction of subobjects unconditionally, not just in C++14.
Summary:
Per https://wg21.link/CWG1677, the C++11 standard did not clarify that constant
initialization of an object allowed constexpr brace-or-equal initialization of
subobjects:
struct foo_t { union { int i; volatile int j; } u; };
__attribute__((__require_constant_initialization__))
static const foo_t x = {{0}};
Because foo_t::u has a volatile member, the initializer for x fails. However,
there is really no good reason, because this:
union foo_u { int i; volatile int j; };
__attribute__((__require_constant_initialization__))
static const foo_u x = {0};
does have a constant initializer.
(This was triggered by musl's pthread_mutex_t type when building under C++11.)
Reviewers: rsmith
Subscribers: EricWF, cfe-commits
Differential Revision: https://reviews.llvm.org/D28427
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@291480 91177308-0d34-0410-b5e6-96231b3b80d8
-rw-r--r-- | lib/AST/ExprConstant.cpp | 13 | ||||
-rw-r--r-- | test/CXX/basic/basic.start/basic.start.init/p2.cpp | 21 | ||||
-rw-r--r-- | test/CodeGenCXX/global-array-destruction.cpp | 6 |
3 files changed, 35 insertions, 5 deletions
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp index fe77c7f6f3..a8512b2940 100644 --- a/lib/AST/ExprConstant.cpp +++ b/lib/AST/ExprConstant.cpp @@ -1627,8 +1627,17 @@ static bool CheckLiteralType(EvalInfo &Info, const Expr *E, // C++1y: A constant initializer for an object o [...] may also invoke // constexpr constructors for o and its subobjects even if those objects // are of non-literal class types. - if (Info.getLangOpts().CPlusPlus14 && This && - Info.EvaluatingDecl == This->getLValueBase()) + // + // C++11 missed this detail for aggregates, so classes like this: + // struct foo_t { union { int i; volatile int j; } u; }; + // are not (obviously) initializable like so: + // __attribute__((__require_constant_initialization__)) + // static const foo_t x = {{0}}; + // because "i" is a subobject with non-literal initialization (due to the + // volatile member of the union). See: + // http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1677 + // Therefore, we use the C++1y behavior. + if (This && Info.EvaluatingDecl == This->getLValueBase()) return true; // Prvalue constant expressions must be of literal types. diff --git a/test/CXX/basic/basic.start/basic.start.init/p2.cpp b/test/CXX/basic/basic.start/basic.start.init/p2.cpp new file mode 100644 index 0000000000..36158210ac --- /dev/null +++ b/test/CXX/basic/basic.start/basic.start.init/p2.cpp @@ -0,0 +1,21 @@ +// RUN: %clang_cc1 -verify %s -pedantic-errors -std=c++11 +// RUN: %clang_cc1 -verify %s -pedantic-errors -std=c++14 +// expected-no-diagnostics + +struct foo_t { + union { + int i; + volatile int j; + } u; +}; + +__attribute__((__require_constant_initialization__)) +static const foo_t x = {{0}}; + +union foo_u { + int i; + volatile int j; +}; + +__attribute__((__require_constant_initialization__)) +static const foo_u y = {0}; diff --git a/test/CodeGenCXX/global-array-destruction.cpp b/test/CodeGenCXX/global-array-destruction.cpp index cb3524b3f0..1ae7b72838 100644 --- a/test/CodeGenCXX/global-array-destruction.cpp +++ b/test/CodeGenCXX/global-array-destruction.cpp @@ -39,7 +39,7 @@ struct T { T t[2][3] = { 1.0, 2, 3.0, 4, 5.0, 6, 7.0, 8, 9.0, 10, 11.0, 12 }; // CHECK: call {{.*}} @__cxa_atexit -// CHECK: getelementptr inbounds ({{.*}} bitcast {{.*}}* @t to %struct.T*), i64 6 +// CHECK: getelementptr inbounds ({{.*}} getelementptr inbounds ([2 x [3 x {{.*}}]], [2 x [3 x {{.*}}]]* @t, i32 0, i32 0, i32 0), i64 6) // CHECK: call void @_ZN1TD1Ev // CHECK: icmp eq {{.*}} @t // CHECK: br i1 {{.*}} @@ -47,9 +47,9 @@ T t[2][3] = { 1.0, 2, 3.0, 4, 5.0, 6, 7.0, 8, 9.0, 10, 11.0, 12 }; static T t2[2][3] = { 1.0, 2, 3.0, 4, 5.0, 6, 7.0, 8, 9.0, 10, 11.0, 12 }; // CHECK: call {{.*}} @__cxa_atexit -// CHECK: getelementptr inbounds ({{.*}} bitcast {{.*}}* @_ZL2t2 to %struct.T*), i64 6 +// CHECK: getelementptr inbounds ({{.*}} getelementptr inbounds ([2 x [3 x {{.*}}]], [2 x [3 x {{.*}}]]* @_ZL2t2, i32 0, i32 0, i32 0), i64 6) // CHECK: call void @_ZN1TD1Ev -// CHECK: icmp eq {{.*}} @_ZL2t +// CHECK: icmp eq {{.*}} @_ZL2t2 // CHECK: br i1 {{.*}} using U = T[2][3]; |