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Bug 990764 - Add MOZ_ASSERT_UNREACHABLE and MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE. r=Waldo

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This commit is contained in:
Chris Peterson 2014-04-05 18:07:09 -07:00
parent 6e781e0384
commit 314cc438bf
1 changed files with 44 additions and 21 deletions
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65
mfbt/Assertions.h
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@ -381,6 +381,16 @@ void ValidateAssertConditionType()
# define MOZ_ASSERT(...) do { } while(0)
#endif /* DEBUG */
/*
* MOZ_NIGHTLY_ASSERT is defined for both debug and release builds on the
* Nightly channel, but only debug builds on Aurora, Beta, and Release.
*/
#if defined(NIGHTLY_BUILD)
# define MOZ_NIGHTLY_ASSERT(...) MOZ_RELEASE_ASSERT(__VA_ARGS__)
#else
# define MOZ_NIGHTLY_ASSERT(...) MOZ_ASSERT(__VA_ARGS__)
#endif
/*
* MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
* true.
@ -403,9 +413,8 @@ void ValidateAssertConditionType()
/*
* MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that it is
* undefined behavior for execution to reach this point. No guarantees are made
* about what will happen if this is reached at runtime. Most code should
* probably use the higher level MOZ_ASSUME_UNREACHABLE, which uses this when
* appropriate.
* about what will happen if this is reached at runtime. Most code should use
* MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE because it has extra asserts.
*/
#if defined(__clang__)
# define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
@ -435,21 +444,22 @@ void ValidateAssertConditionType()
#endif
/*
* MOZ_ASSUME_UNREACHABLE([reason]) tells the compiler that it can assume that
* the macro call cannot be reached during execution. This lets the compiler
* generate better-optimized code under some circumstances, at the expense of
* the program's behavior being undefined if control reaches the
* MOZ_ASSUME_UNREACHABLE.
* MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE([reason]) tells the compiler that it
* can assume that the macro call cannot be reached during execution. This lets
* the compiler generate better-optimized code under some circumstances, at the
* expense of the program's behavior being undefined if control reaches the
* MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE.
*
* In Gecko, you probably should not use this macro outside of performance- or
* size-critical code, because it's unsafe. If you don't care about code size
* or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
*
* SpiderMonkey is a different beast, and there it's acceptable to use
* MOZ_ASSUME_UNREACHABLE more widely.
* MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE more widely.
*
* Note that MOZ_ASSUME_UNREACHABLE is noreturn, so it's valid not to return a
* value following a MOZ_ASSUME_UNREACHABLE call.
* Note that MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE is noreturn, so it's valid
* not to return a value following a MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE
* call.
*
* Example usage:
*
@ -469,19 +479,32 @@ void ValidateAssertConditionType()
* case VALUE_FLOAT:
* return (int) *(float*) value;
* default:
* MOZ_ASSUME_UNREACHABLE("can only handle VALUE_INT and VALUE_FLOAT");
* MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected ValueType");
* }
* }
*/
#if defined(DEBUG)
# define MOZ_ASSUME_UNREACHABLE(...) \
do { \
MOZ_ASSERT(false, "MOZ_ASSUME_UNREACHABLE(" __VA_ARGS__ ")"); \
MOZ_ASSUME_UNREACHABLE_MARKER(); \
} while (0)
#else
# define MOZ_ASSUME_UNREACHABLE(reason) MOZ_ASSUME_UNREACHABLE_MARKER()
#endif
/*
* Assert in all debug builds plus the Nightly channel's release builds. Take
* this extra testing precaution because hitting MOZ_ASSUME_UNREACHABLE_MARKER
* could trigger exploitable undefined behavior.
*/
#define MOZ_ASSERT_UNREACHABLE(reason) \
MOZ_NIGHTLY_ASSERT(false, "MOZ_ASSERT_UNREACHABLE: " reason)
#define MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason) \
do { \
MOZ_ASSERT_UNREACHABLE(reason); \
MOZ_ASSUME_UNREACHABLE_MARKER(); \
} while (0)
/*
* TODO: Bug 990764: Audit all MOZ_ASSUME_UNREACHABLE calls and replace them
* with MOZ_ASSERT_UNREACHABLE, MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE, or
* MOZ_CRASH. For now, preserve the macro's same meaning of unreachable.
*/
#define MOZ_ASSUME_UNREACHABLE(reason) \
MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason)
/*
* MOZ_ALWAYS_TRUE(expr) and MOZ_ALWAYS_FALSE(expr) always evaluate the provided