BranchTest.cpp

#include <stdlib.h>
#include <vector>
#include <intrin.h>
#include <stdint.h>
#include <inttypes.h>

std::vector<char> makeTestVector( bool random )
{
	std::vector<char> result;
	result.resize( 1024 * 16 );
	if( random )
	{
		srand( 0 );
		for( char& ref : result )
			ref = ( rand() & 1 ) ? 1 : 0;
	}
	else
	{
		for( size_t i = 0; i < result.size(); i++ )
			result[ i ] = ( i & 1 ) ? 1 : 0;
	}
	return result;
}

static size_t __declspec( noinline ) one()
{
	return 1;
}
size_t countWithBranches( const std::vector<char>& vec )
{
	size_t res = 0;

	const int64_t tsc = (int64_t)__rdtsc();
	_ReadBarrier();

	for( char c : vec )
	{
		if( c )
			res += one();
	}

	const int64_t elapsed = (int64_t)__rdtsc() - tsc;
	printf( "Elapsed time: %" PRIi64 "\n", elapsed );
	return res;
}

int main()
{
	// Flip this to true, re-compile, and retry
	constexpr bool random = false;
	const auto vec = makeTestVector( random );
	size_t res = countWithBranches( vec );
	printf( "Counter: %zu\n", res );
	return 0;
}