[clang] [clang][Interp] Implement __builtin_bit_cast (PR #68288)

[Aaron Ballman via cfe-commits]

Timm =?utf-8?q?Bäder?= <tbaeder at redhat.com>,
Timm =?utf-8?q?Bäder?= <tbaeder at redhat.com>,
Timm =?utf-8?q?Bäder?= <tbaeder at redhat.com>,
Timm =?utf-8?q?Bäder?= <tbaeder at redhat.com>,
Timm =?utf-8?q?Bäder?= <tbaeder at redhat.com>,
Timm =?utf-8?q?Bäder?= <tbaeder at redhat.com>
Message-ID:
In-Reply-To: <llvm/llvm-project/pull/68288/clang at github.com>


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@@ -0,0 +1,816 @@
+// RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -fexperimental-new-constant-interpreter %s
+// RUN: %clang_cc1 -verify=ref -std=c++2a -fsyntax-only %s
+// RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -triple aarch64_be-linux-gnu -fexperimental-new-constant-interpreter %s
+// RUN: %clang_cc1 -verify=ref -std=c++2a -fsyntax-only -triple aarch64_be-linux-gnu %s
+// RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -fexperimental-new-constant-interpreter -triple powerpc64le-unknown-unknown -mabi=ieeelongdouble %s
+// RUN: %clang_cc1 -verify=ref -std=c++2a -fsyntax-only -triple powerpc64le-unknown-unknown -mabi=ieeelongdouble %s
+// RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -fexperimental-new-constant-interpreter -triple powerpc64-unknown-unknown -mabi=ieeelongdouble %s
+// RUN: %clang_cc1 -verify=ref -std=c++2a -fsyntax-only -triple powerpc64-unknown-unknown -mabi=ieeelongdouble %s
+
+/// FIXME: This is a version of
+///   clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp with the currently
+///   supported subset of operations. They should *all* be supported though.
+
+
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#  define LITTLE_END 1
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#  define LITTLE_END 0
+#else
+#  error "huh?"
+#endif
+
+typedef decltype(nullptr) nullptr_t;
+
+
+
+static_assert(sizeof(int) == 4);
+static_assert(sizeof(long long) == 8);
+
+template <class To, class From>
+constexpr To bit_cast(const From &from) {
+  static_assert(sizeof(To) == sizeof(From));
+  return __builtin_bit_cast(To, from); // ref-note 2{{indeterminate value can only initialize}} \
+                                       // expected-note 2{{indeterminate value can only initialize}} \
+                                       // ref-note {{subexpression not valid}}
+}
+
+
+/// Current interpreter does not support this.
+/// https://github.com/llvm/llvm-project/issues/63686
+constexpr int FromString = bit_cast<int>("abc"); // ref-error {{must be initialized by a constant expression}} \
+                                                 // ref-note {{in call to}} \
+                                                 // ref-note {{declared here}}
+#if LITTLE_END
+static_assert(FromString == 6513249); // ref-error {{is not an integral constant expression}} \
+                                      // ref-note {{initializer of 'FromString' is not a constant expression}}
+#else
+static_assert(FromString == 1633837824); // ref-error {{is not an integral constant expression}} \
----------------
AaronBallman wrote:

Are these values actually stable? I think this is bit-casting the pointer value for the string literal itself, so I would assume that pointer value isn't stable.

https://github.com/llvm/llvm-project/pull/68288