Hi!
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.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
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.
--- gcc/fold-const.cc.jj 2024-03-26 11:21:31.996860739 +0100
+++ gcc/fold-const.cc 2024-04-03 16:59:05.747297410 +0200
@@ -8601,6 +8601,8 @@ native_encode_initializer (tree init, un
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;
--- gcc/testsuite/g++.dg/cpp2a/bit-cast16.C.jj 2024-04-03 17:06:46.720974426
+0200
+++ gcc/testsuite/g++.dg/cpp2a/bit-cast16.C 2024-04-03 17:06:40.233063410
+0200
@@ -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);
Jakub
