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fold-const: Handle NON_LVALUE_EXPR in native_encode_initializer [PR114537]

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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  <jakub@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.
This commit is contained in:
Jakub Jelinek 2024-04-04 10:47:52 +02:00
parent 48530efdcc
commit 1baec8deb0
2 changed files with 18 additions and 0 deletions
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2
gcc/fold-const.cc
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@ -8601,6 +8601,8 @@ 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;

16
gcc/testsuite/g++.dg/cpp2a/bit-cast16.C Normal file
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@ -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);