[lldb] fix build issue on MSVC because of missing byte-swap builtins

[ashay-github]

Summary

The __builtin_bswap{32,64}() builtins (introduced in commit e07a421d)
are missing from MSVC, which causes build errors when compiling LLDB on
Windows (tested with MSVC 19.34.31943.0). This patch replaces the
builtins with either MSVC's _byteswap_u{long,64}() or the original
builtins, or the bswap_{32,64}() functions from byteswap.h, depending
on which ones are available.

[bulbazord]

Instead of not using __builtin_bswap{32,64} entirely, we should check if they're available.

You can use the clang feature-checking macro __has_builtin (and if it doesn't exist you can define it). So you could amend this patch like so:

#if !defined(__has_builtin)
#define __has_builtin(x) 0
#endif

#if __has_builtin(__builtin_bswap32)
#define bswap_32(x) __builtin_bswap32(x)
#elif _MSC_VER
#define bswap_32(x) _byteswap_ulong(x)
#else
#include <byteswap.h>
#endif

[ashay-github]

Updated to check for builtins and use them, if available.

[bulbazord]

LGTM

[DavidSpickett]

Thanks for the fix!

Made me realise I should have looked harder for an llvm utility in the first place, and it turns out llvm::byteswap exists. So I've changed this to use that in https://github.com/llvm/llvm-project/commit/9984cfc86ed6d5c1558d8dd82d82448e50d704ad.

[DavidSpickett]

By the way, did this come up on a bot? Just wondering if I ignored an email, apologies if so.

[ashay-github]

The llvm::byteswap() fix is much nicer. Thanks for the change!

No, this build error didn't show up on a bot (at least as far as I can tell).

lldb/source/Core/DumpRegisterValue.cpp

 #include "lldb/DataFormatters/DumpValueObjectOptions.h"
 #include "lldb/Target/RegisterFlags.h"
 #include "lldb/Utility/DataExtractor.h"
 #include "lldb/Utility/Endian.h"
 #include "lldb/Utility/RegisterValue.h"
 #include "lldb/Utility/StreamString.h"
 #include "lldb/lldb-private-types.h"
 
+#if !defined(__has_builtin)
+#define __has_builtin(x) 0
+#endif
+
+#if __has_builtin(__builtin_bswap32) && __has_builtin(__builtin_bswap64)
+#define bswap_32(x) __builtin_bswap32(x)
+#define bswap_64(x) __builtin_bswap64(x)
+#elif defined(_MSC_VER)
+#define bswap_32(x) _byteswap_ulong(x)
+#define bswap_64(x) _byteswap_uint64(x)
+#else
+#include <byteswap.h>
+#endif
+
 using namespace lldb;
 
-static uint32_t swap_value(uint32_t v) { return __builtin_bswap32(v); }
-static uint64_t swap_value(uint64_t v) { return __builtin_bswap64(v); }
+static uint32_t swap_value(uint32_t v) { return bswap_32(v); }
+static uint64_t swap_value(uint64_t v) { return bswap_64(v); }
 
 template <typename T>
 static void dump_type_value(lldb_private::CompilerType &fields_type, T value,
                             lldb_private::ExecutionContextScope *exe_scope,
                             const lldb_private::RegisterInfo &reg_info,
                             lldb_private::Stream &strm) {
   lldb::ByteOrder target_order = exe_scope->CalculateProcess()->GetByteOrder();