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  <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.

(cherry picked from commit 1baec8deb014b8a7da58879a407a4c00cdeb5a09)

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 31ae6cebbe6ba976388f6b7f41b5ffc194e1cae9..25dd7c1094ee881efc7dd499f18a97821a3dd00e 100644 (file)
--- 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 (file)
index 0000000..d298af6
--- /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);