http://llvm.org/bugs/show_bug.cgi?id=16754
Bug ID: 16754
Summary: Probable pessimization in steady_clock
Product: libc++
Version: unspecified
Hardware: PC
OS: MacOS X
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
There is a comment in chrono.cpp
// MachInfo.numer / MachInfo.denom is often 1 on the latest equipment.
Specialize
// for that case as an optimization.
This comment points to:
steady_clock::time_point
steady_clock::now() _NOEXCEPT
{
static FP fp = init_steady_clock();
return time_point(duration(fp()));
}
Which replaces a double precision multiply with a call through a function
pointer as an optimization.
static
steady_clock::rep
steady_full()
{
static const double factor = compute_steady_factor();
return static_cast<steady_clock::rep>(mach_absolute_time() * factor);
}
vs
static
steady_clock::rep
steady_simplified()
{
return static_cast<steady_clock::rep>(mach_absolute_time());
}
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