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RTC_LOG(): Internally, pass logging severity as template argument

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When the logging severity is statically known, passing it as a
template argument instead of as a function argument saves space at the
call site.

Because this is a constructor, it's not possible to pass template
arguments explicitly---they need to be deduced. So we pass a dummy
function argument whose type encodes the logging severity, and because
the dummy is an empty struct, the ABI generally specifies that this is
a no-op with no runtime cost.

In aggregate, this reduces the size of libjingle_peerconnection_so.so
by 4 kB.

Bug: webrtc:9185
Change-Id: I8118f39dc2aed3be34b2979a239fc0d3dffa969f
Reviewed-on: https://webrtc-review.googlesource.com/74582
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23136}
This commit is contained in:
Karl Wiberg 2018-05-04 15:04:48 +02:00 committed by Commit Bot
parent a4e37a8f82
commit 1ffb3747bd
1 changed files with 15 additions and 3 deletions
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18
rtc_base/logging.h
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@ -123,6 +123,16 @@ class LogSink {
class LogMessage {
public:
LogMessage(const char* file, int line, LoggingSeverity sev);
// Same as the above, but using a compile-time constant for the logging
// severity. This saves space at the call site, since passing an empty struct
// is generally the same as not passing an argument at all.
template <LoggingSeverity S>
RTC_NO_INLINE LogMessage(const char* file,
int line,
std::integral_constant<LoggingSeverity, S>)
: LogMessage(file, line, S) {}
LogMessage(const char* file,
int line,
LoggingSeverity sev,
@ -281,9 +291,11 @@ class LogMessageVoidify {
#define RTC_LOG_SEVERITY_PRECONDITION_C(sev) \
!(rtc::LogMessage::Loggable<rtc::sev>()) ? (void)0 : rtc::LogMessageVoidify()&
#define RTC_LOG(sev) \
RTC_LOG_SEVERITY_PRECONDITION_C(sev) \
rtc::LogMessage(__FILE__, __LINE__, rtc::sev).stream()
#define RTC_LOG(sev) \
RTC_LOG_SEVERITY_PRECONDITION_C(sev) \
rtc::LogMessage(__FILE__, __LINE__, \
std::integral_constant<rtc::LoggingSeverity, rtc::sev>()) \
.stream()
// The _V version is for when a variable is passed in. It doesn't do the
// namespace concatenation.