https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86974
Bug ID: 86974
Summary: Support Clang's require_constant_initialization
attribute
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: enhancement
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
As documented at
https://clang.llvm.org/docs/AttributeReference.html#require-constant-initialization-clang-require-constant-initialization
This attribute is very useful to check that a global uses constant
initialization, thus avoiding the Static Initialization Order Fiasco.
For example, see PR 83428 where it was mistakenly believed that the variable
should not be dynamically initialized, but actually there was a bug in the code
preventing it.
If the variable will not get constant initialization Clang gives an error and
states the reason for dynamic init:
83428.cc:20:54: error: variable does not have a constant initializer
__attribute__((require_constant_initialization)) S2 objX;
^~~~
83428.cc:20:17: note: required by 'require_constant_initialization' attribute
here
__attribute__((require_constant_initialization)) S2 objX;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
83428.cc:12:7: note: undefined constructor 'S1' cannot be used in a constant
expression
: m_tabS1()
^
83428.cc:20:54: note: in call to 'S2()'
__attribute__((require_constant_initialization)) S2 objX;
^
83428.cc:3:15: note: declared here
constexpr S1 ();
^
1 error generated.
So this doesn't change the meaning of any code, it just acts as an assertion
that a property is true.
