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c++: strict constexpr and local vars 

A change I was working on made constexpr_searcher.cc start to fail, and when
I looked at it I wondered why it had been accepted before.  This turned out
to be because we try to be more flexible about constant-evaluation of static
initializers, as allowed, but we were wrongly doing the same for non-static
initializers as well.

gcc/cp/ChangeLog:

	* constexpr.cc (maybe_constant_init_1): Only pass false for
	strict when initializing a variable of static duration.

libstdc++-v3/ChangeLog:

	* testsuite/20_util/function_objects/constexpr_searcher.cc: Add
	constexpr.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/constexpr-local4.C: New test.
This commit is contained in:
Jason Merrill 2022-05-22 15:04:33 -04:00
parent 1b661f3f5e
commit 6209009df6
3 changed files with 28 additions and 5 deletions
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12
gcc/cp/constexpr.cc
View File

@ -8301,9 +8301,15 @@ maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant,
else if (CONSTANT_CLASS_P (t) && allow_non_constant)
/* No evaluation needed. */;
else
t = cxx_eval_outermost_constant_expr (t, allow_non_constant,
/*strict*/false,
manifestly_const_eval, false, decl);
{
/* [basic.start.static] allows constant-initialization of variables with
static or thread storage duration even if it isn't required, but we
shouldn't bend the rules the same way for automatic variables. */
bool is_static = (decl && DECL_P (decl)
&& (TREE_STATIC (decl) || DECL_EXTERNAL (decl)));
t = cxx_eval_outermost_constant_expr (t, allow_non_constant, !is_static,
manifestly_const_eval, false, decl);
}
if (TREE_CODE (t) == TARGET_EXPR)
{
tree init = TARGET_EXPR_INITIAL (t);

17
gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C Normal file
View File

@ -0,0 +1,17 @@
// { dg-do compile { target c++14 } }
struct A
{
int i;
constexpr A(int i): i(i) {};
};
const A a = 42;
constexpr int f()
{
const int j = a.i; // { dg-message "'a'" }
return j;
}
static_assert (f() == 42,""); // { dg-error "non-constant" }

4
libstdc++-v3/testsuite/20_util/function_objects/constexpr_searcher.cc
View File

@ -28,13 +28,13 @@
#include <string_view>
const std::string_view
constexpr std::string_view
patt = "World";
constexpr std::string_view
greet = "Hello, Humongous World of Wonder!!!";
const std::wstring_view
constexpr std::wstring_view
wpatt = L"World";
constexpr std::wstring_view