| Summary: | comparison of address of template variables should be constexpr | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Francesco Biscani <bluescarni> |
| Component: | c++ | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED DUPLICATE | ||
| Severity: | normal | CC: | daniel.kruegler, jason, johelegp, marxin, mpolacek, pdimov, sjeltsch, webrown.cpp |
| Priority: | P3 | Keywords: | rejects-valid |
| Version: | 10.0 | ||
| Target Milestone: | --- | ||
| See Also: |
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69681 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85428 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89367 |
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| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2020-04-23 00:00:00 | |
| Bug Depends on: | |||
| Bug Blocks: | 55004 | ||
Confirmed, ale GCC versions suffer. Reduced testcase: template <int> char test_impl = 0; static_assert(&test_impl<0> != &test_impl<1>, "should not be equal"); *** Bug 102267 has been marked as a duplicate of this bug. *** The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>: https://gcc.gnu.org/g:91031bffa42fdea3c985727d042cd1882a64be9c commit r12-6188-g91031bffa42fdea3c985727d042cd1882a64be9c Author: Jakub Jelinek <jakub@redhat.com> Date: Mon Jan 3 13:47:53 2022 +0100 symtab: Fold &a == &b to 0 if folding_initializer [PR94716] On Thu, Dec 09, 2021 at 06:09:12PM -0500, Jason Merrill wrote: > For the more general comparison of decls like your a != b example above I > think clang is in the right; in manifestly constant-evaluated context > (folding_initializer) we should return that they are unequal and prevent a > later alias declaration, like we do for comparison to 0 in > maybe_nonzero_address. It's possible that this gives a wrong answer based > on something in another translation unit, but that's unlikely, and taking > that chance seems better than rejecting code that needs a constant answer. I agree. This is an incremental patch to do that. 2022-01-03 Jakub Jelinek <jakub@redhat.com> PR c++/94716 gcc/ * symtab.c: Include fold-const.h. (symtab_node::equal_address_to): If folding_initializer is true, handle it like memory_accessed. Simplify. gcc/testsuite/ * gcc.dg/init-compare-1.c: New test. * g++.dg/cpp0x/constexpr-compare1.C: New test. * g++.dg/cpp1y/constexpr-94716.C: New test. * g++.dg/cpp1z/constexpr-compare1.C: New test. *** Bug 101622 has been marked as a duplicate of this bug. *** |
The following code does not compile in GCC trunk: ----- template <typename T> inline constexpr char test_impl = 0; template <typename T> inline constexpr auto *id = &test_impl<T>; int main() { static_assert(id<int> != id<float>, "should not be equal"); } ----- The error message: ----- <source>: In function 'int main()': <source>:8:27: error: non-constant condition for static assertion 8 | static_assert(id<int> != id<float>, "should not be equal"); | ~~~~~~~~^~~~~~~~~~~~ <source>:8:27: error: '((& test_impl<int>) != (& test_impl<float>))' is not a constant expression Compiler returned: 1 ----- See on godbolt: https://godbolt.org/z/CS4D8B Clang and MSVC accept the code.