https://gcc.gnu.org/g:a297f9bbb9611414fe48f6d61a8829bf5808bd2c
commit r13-8626-ga297f9bbb9611414fe48f6d61a8829bf5808bd2c Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Apr 4 10:47:52 2024 +0200 fold-const: Handle NON_LVALUE_EXPR in native_encode_initializer [PR114537] The following testcase is incorrectly rejected. The problem is that for bit-fields native_encode_initializer expects the corresponding CONSTRUCTOR elt value must be INTEGER_CST, but that isn't the case here, it is wrapped into NON_LVALUE_EXPR by maybe_wrap_with_location. We could STRIP_ANY_LOCATION_WRAPPER as well, but as all we are looking for is INTEGER_CST inside, just looking through NON_LVALUE_EXPR seems easier. 2024-04-04 Jakub Jelinek <ja...@redhat.com> PR c++/114537 * fold-const.cc (native_encode_initializer): Look through NON_LVALUE_EXPR if val is INTEGER_CST. * g++.dg/cpp2a/bit-cast16.C: New test. (cherry picked from commit 1baec8deb014b8a7da58879a407a4c00cdeb5a09) Diff: --- gcc/fold-const.cc | 2 ++ gcc/testsuite/g++.dg/cpp2a/bit-cast16.C | 16 ++++++++++++++++ 2 files changed, 18 insertions(+) diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc index 31ae6cebbe6..25dd7c1094e 100644 --- a/gcc/fold-const.cc +++ b/gcc/fold-const.cc @@ -8485,6 +8485,8 @@ native_encode_initializer (tree init, unsigned char *ptr, int len, if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN) return 0; + if (TREE_CODE (val) == NON_LVALUE_EXPR) + val = TREE_OPERAND (val, 0); if (TREE_CODE (val) != INTEGER_CST) return 0; diff --git a/gcc/testsuite/g++.dg/cpp2a/bit-cast16.C b/gcc/testsuite/g++.dg/cpp2a/bit-cast16.C new file mode 100644 index 00000000000..d298af67ef2 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/bit-cast16.C @@ -0,0 +1,16 @@ +// PR c++/114537 +// { dg-do compile { target c++20 } } + +namespace std { +template<typename T, typename F> +constexpr T +bit_cast (const F& f) noexcept +{ + return __builtin_bit_cast (T, f); +} +} + +struct A { signed char b : 1 = 0; signed char c : 7 = 0; }; +struct D { unsigned char e; }; +constexpr unsigned char f = std::bit_cast<D> (A{}).e; +static_assert (f == 0);