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c++: Fix constexpr cleanup error handling.

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In this testcase, the primary evaluation successfully produces 'true', and
then running one of the cleanups hits a double delete, making the whole
thing not a valid constant expression.  So we were returning 'true' wrapped
in a NOP_EXPR to indicate its non-constancy, but evaluating that again is a
perfectly acceptable constant expression, so we weren't getting the verbose
diagnostic we were looking for.

So if non_constant_p gets set other than for overflow, go back to the
original expression.

With this change, we should never hit the manifestly_const_eval test, and
the is-constant-evaluated1.C test passes without it.

gcc/cp/ChangeLog:

	PR c++/97388
	* constexpr.c (cxx_eval_outermost_constant_expr): Revert to
	original expression if evaluation sets non_constant_p.

gcc/testsuite/ChangeLog:

	PR c++/97388
	* g++.dg/cpp2a/constexpr-dtor8.C: New test.
This commit is contained in:
Jason Merrill 2020-10-28 17:30:05 -04:00
parent 5afd90c5f3
commit 8895443a42
2 changed files with 23 additions and 6 deletions
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10
gcc/cp/constexpr.c
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@ -6925,6 +6925,10 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
non_constant_p = true;
}
if (non_constant_p)
/* If we saw something bad, go back to our argument. The wrapping below is
only for the cases of TREE_CONSTANT argument or overflow. */
r = t;
if (!non_constant_p && overflow_p)
non_constant_p = true;
@ -6941,12 +6945,6 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
return r;
else if (non_constant_p && TREE_CONSTANT (r))
{
/* If __builtin_is_constant_evaluated () was evaluated to true
and the result is not a valid constant expression, we need to
punt. */
if (manifestly_const_eval)
return cxx_eval_outermost_constant_expr (t, true, strict,
false, false, object);
/* This isn't actually constant, so unset TREE_CONSTANT.
Don't clear TREE_CONSTANT on ADDR_EXPR, as the middle-end requires
it to be set if it is invariant address, even when it is not

19
gcc/testsuite/g++.dg/cpp2a/constexpr-dtor8.C Normal file
View File

@ -0,0 +1,19 @@
// PR c++/97388
// { dg-do compile { target c++20 } }
struct S {
int *s;
constexpr S () : s(new int) {}
S (const S &) = delete;
S &operator= (const S &) = delete;
constexpr ~S () { delete s; } // { dg-error "already deallocated" }
};
constexpr bool
foo (S v)
{
delete v.s;
return true;
}
static_assert (foo (S ())); // { dg-error "non-constant condition for static assertion" }