d3d12: Add a unreachable function used as debug/optimisation hint

rpcs3/Emu/RSX/D3D12/D3D12Utils.cpp

@@ -262,4 +262,13 @@ void D3D12GSRender::initConvertShader()
 	p.first->Release();
 	p.second->Release();
 }
+
+void unreachable_internal(const char *msg, const char *file, unsigned line)
+{
+	abort();
+	#ifdef LLVM_BUILTIN_UNREACHABLE
+		LLVM_BUILTIN_UNREACHABLE;
+	#endif
+}
+
 #endif

rpcs3/Emu/RSX/D3D12/D3D12Utils.h

@@ -7,6 +7,63 @@
 #include "Emu/Memory/vm.h"
 #include "Emu/RSX/GCM.h"
 
+
+// From llvm Compiler.h
+
+// Need to be set by define
+#ifndef __has_builtin
+#define __has_builtin(x) 0
+#endif
+
+/// \macro LLVM_GNUC_PREREQ
+/// \brief Extend the default __GNUC_PREREQ even if glibc's features.h isn't
+/// available.
+#ifndef LLVM_GNUC_PREREQ
+# if defined(__GNUC__) && defined(__GNUC_MINOR__) && defined(__GNUC_PATCHLEVEL__)
+#define LLVM_GNUC_PREREQ(maj, min, patch) \
+	((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) + __GNUC_PATCHLEVEL__ >= \
+	((maj) << 20) + ((min) << 10) + (patch))
+# elif defined(__GNUC__) && defined(__GNUC_MINOR__)
+#define LLVM_GNUC_PREREQ(maj, min, patch) \
+	((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) >= ((maj) << 20) + ((min) << 10))
+#else
+#define LLVM_GNUC_PREREQ(maj, min, patch) 0
+#endif
+#endif
+
+#ifdef __GNUC__
+#define LLVM_ATTRIBUTE_NORETURN __attribute__((noreturn))
+#elif defined(_MSC_VER)
+#define LLVM_ATTRIBUTE_NORETURN __declspec(noreturn)
+#else
+#define LLVM_ATTRIBUTE_NORETURN
+#endif
+
+#if __has_builtin(__builtin_unreachable) || LLVM_GNUC_PREREQ(4, 5, 0)
+# define LLVM_BUILTIN_UNREACHABLE __builtin_unreachable()
+#elif defined(_MSC_VER)
+# define LLVM_BUILTIN_UNREACHABLE __assume(false)
+#endif
+
+LLVM_ATTRIBUTE_NORETURN void unreachable_internal(const char *msg = nullptr, const char *file = nullptr, unsigned line = 0);
+
+/// Marks that the current location is not supposed to be reachable.
+/// In !NDEBUG builds, prints the message and location info to stderr.
+/// In NDEBUG builds, becomes an optimizer hint that the current location
+/// is not supposed to be reachable.  On compilers that don't support
+/// such hints, prints a reduced message instead.
+///
+/// Use this instead of assert(0).  It conveys intent more clearly and
+/// allows compilers to omit some unnecessary code.
+#ifndef NDEBUG
+#define unreachable(msg) \
+	unreachable_internal(msg, __FILE__, __LINE__)
+#elif defined(LLVM_BUILTIN_UNREACHABLE)
+#define unreachable(msg) LLVM_BUILTIN_UNREACHABLE
+#else
+#define unreachable(msg) unreachable_internal()
+#endif
+
 using namespace Microsoft::WRL;
 
 // From DX12 D3D11On12 Sample (MIT Licensed)