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Improve RTC_DCHECK_op so that it won't trigger useless compiler warnings

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Before this change, with DCHECKs switched off, this sort of check

  size_t index = ...;
  RTC_DCHECK_GE(index, 0u);

would cause GCC (but no other compiler that we use) to complain
that unsigned values are always greater than or equal to 0. With
this change, it no longer complains.

(It was and remains the case that there was no complaints if
DCHECKs were switched on, or if you used RTC_CHECK_op.)

The reason for doing this change is that it isn't useful for the
compiler to force us to remove DCHECKs just because their
condition can be verified statically. That causes us to remove
the checks, and once that's happened, future code changes are free
to violate the removed checks and no one will know...

BUG=webrtc:6620

Review-Url: https://codereview.webrtc.org/2455943002
Cr-Commit-Position: refs/heads/master@{#14805}
This commit is contained in:
kwiberg 2016-10-27 13:35:59 -07:00 committed by Commit bot
parent a73df559d6
commit 32bcaf61f5
1 changed files with 18 additions and 10 deletions
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28
webrtc/base/checks.h
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@ -83,16 +83,24 @@ namespace rtc {
#define RTC_LAZY_STREAM(stream, condition) \
!(condition) ? static_cast<void>(0) : rtc::FatalMessageVoidify() & (stream)
// The actual stream used isn't important. We reference condition in the code
// The actual stream used isn't important. We reference |ignored| in the code
// but don't evaluate it; this is to avoid "unused variable" warnings (we do so
// in a particularly convoluted way with an extra ?: because that appears to be
// the simplest construct that keeps Visual Studio from complaining about
// condition being unused).
#define RTC_EAT_STREAM_PARAMETERS(condition) \
(true ? true : !(condition)) \
? static_cast<void>(0) \
#define RTC_EAT_STREAM_PARAMETERS(ignored) \
(true ? true : ((void)(ignored), true)) \
? static_cast<void>(0) \
: rtc::FatalMessageVoidify() & rtc::FatalMessage("", 0).stream()
// Call RTC_EAT_STREAM_PARAMETERS with an argument that fails to compile if
// values of the same types as |a| and |b| can't be compared with the given
// operation, and that would evaluate |a| and |b| if evaluated.
#define RTC_EAT_STREAM_PARAMETERS_OP(op, a, b) \
RTC_EAT_STREAM_PARAMETERS(((void)sizeof(std::declval<decltype(a)>() \
op std::declval<decltype(b)>()), \
(void)(a), (void)(b)))
// RTC_CHECK dies with a fatal error if condition is not true. It is *not*
// controlled by NDEBUG or anything else, so the check will be executed
// regardless of compilation mode.
@ -193,12 +201,12 @@ DEFINE_RTC_CHECK_OP_IMPL(GT, > )
#define RTC_DCHECK_GT(v1, v2) RTC_CHECK_GT(v1, v2)
#else
#define RTC_DCHECK(condition) RTC_EAT_STREAM_PARAMETERS(condition)
#define RTC_DCHECK_EQ(v1, v2) RTC_EAT_STREAM_PARAMETERS((v1) == (v2))
#define RTC_DCHECK_NE(v1, v2) RTC_EAT_STREAM_PARAMETERS((v1) != (v2))
#define RTC_DCHECK_LE(v1, v2) RTC_EAT_STREAM_PARAMETERS((v1) <= (v2))
#define RTC_DCHECK_LT(v1, v2) RTC_EAT_STREAM_PARAMETERS((v1) < (v2))
#define RTC_DCHECK_GE(v1, v2) RTC_EAT_STREAM_PARAMETERS((v1) >= (v2))
#define RTC_DCHECK_GT(v1, v2) RTC_EAT_STREAM_PARAMETERS((v1) > (v2))
#define RTC_DCHECK_EQ(v1, v2) RTC_EAT_STREAM_PARAMETERS_OP(==, v1, v2)
#define RTC_DCHECK_NE(v1, v2) RTC_EAT_STREAM_PARAMETERS_OP(!=, v1, v2)
#define RTC_DCHECK_LE(v1, v2) RTC_EAT_STREAM_PARAMETERS_OP(<=, v1, v2)
#define RTC_DCHECK_LT(v1, v2) RTC_EAT_STREAM_PARAMETERS_OP(<, v1, v2)
#define RTC_DCHECK_GE(v1, v2) RTC_EAT_STREAM_PARAMETERS_OP(>=, v1, v2)
#define RTC_DCHECK_GT(v1, v2) RTC_EAT_STREAM_PARAMETERS_OP(>, v1, v2)
#endif
// This is identical to LogMessageVoidify but in name.