Shorten IMMEDIATE_CRASH() code size on win clang

base/logging.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_LOGGING_H_
 #define BASE_LOGGING_H_
 
 #include <stddef.h>
 
 #include <cassert>
@@ skipping 538 matching lines @@
     TRAP_SEQUENCE();         \
     __builtin_unreachable(); \
   })
 
 #elif defined(COMPILER_MSVC)
 
 // Clang is cleverer about coalescing int3s, so we need to add a unique-ish
 // instruction following the __debugbreak() to have it emit distinct locations
 // for CHECKs rather than collapsing them all together. It would be nice to use
 // a short intrinsic to do this (and perhaps have only one implementation for
-// both clang and MSVC), however clang-cl currently does not support intrinsics
-// here. Adding the nullptr store to the MSVC path adds unnecessary bloat.
+// both clang and MSVC), however clang-cl currently does not support intrinsics.
+// On the flip side, MSVC x64 doesn't support inline asm. So, we have to have
+// two implementations. Normally clang-cl's version will be 5 bytes (1 for
+// `int3`, 2 for `ud2`, 2 for `push byte imm`, however, TODO(scottmg):
+// https://crbug.com/694670 clang-cl doesn't currently support %'ing
+// __COUNTER__, so eventually it will emit the dword form of push.
 // TODO(scottmg): Reinvestigate a short sequence that will work on both
 // compilers once clang supports more intrinsics. See https://crbug.com/693713.
 #if defined(__clang__)
-#define IMMEDIATE_CRASH()                                                 \
-  (__debugbreak(), (void)(*reinterpret_cast<volatile unsigned char*>(0) = \
-                              static_cast<unsigned char>(__COUNTER__)))
+#define IMMEDIATE_CRASH() ({__asm int 3 __asm ud2 __asm push __COUNTER__})
 #else
 #define IMMEDIATE_CRASH() __debugbreak()
 #endif  // __clang__
 
 #else
 #error Port
 #endif
 
 // CHECK dies with a fatal error if condition is not true.  It is *not*
 // controlled by NDEBUG, so the check will be executed regardless of
@@ skipping 547 matching lines @@
 #elif NOTIMPLEMENTED_POLICY == 5
 #define NOTIMPLEMENTED() do {\
   static bool logged_once = false;\
   LOG_IF(ERROR, !logged_once) << NOTIMPLEMENTED_MSG;\
   logged_once = true;\
 } while(0);\
 EAT_STREAM_PARAMETERS
 #endif
 
 #endif  // BASE_LOGGING_H_