Clang Optimisation Bug

main.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>

int sum(int a, int b, int c, int d) {
	return a + b + c + d;
}

int product(int a, int b, int c, int d) {
	return a * b * c * d;
}

int expression(int x) {
	return (x ? sum : product)(1, 2, 3, 4);
}

int statement(int x) {
	if (x)
		return sum(1, 2, 3, 4);
	else
		return product(1, 2, 3, 4);
}

int main() {
	int i;
	struct timeval
		start_expression,
		end_expression,
		start_statement,
		end_statement;
	double
		elapsed_expression,
		elapsed_statement;
	int x = 0;
	const int samples = 10000000;
	srand(time(NULL));
	gettimeofday(&start_expression, NULL);
	for (i = 0; i < samples; ++i)
		x += expression(rand() & 1);
	gettimeofday(&end_expression, NULL);
	printf("%d\n", x);
	x = 0;
	gettimeofday(&start_statement, NULL);
	for (i = 0; i < samples; ++i)
		x += statement(rand() & 1);
	gettimeofday(&end_statement, NULL);
	printf("%d\n", x);
	elapsed_statement
		= (double)end_statement.tv_sec
		+ (double)end_statement.tv_usec * 1e-6
		- (double)start_statement.tv_sec
		- (double)start_statement.tv_usec * 1e-6;
	elapsed_expression
		= (double)end_expression.tv_sec
		+ (double)end_expression.tv_usec * 1e-6
		- (double)start_expression.tv_sec
		- (double)start_expression.tv_usec * 1e-6;
	printf(
		"expression: %.2f\n"
		"statement: %.2f\n"
		"expression is %.2f%% slower than statement\n",
		elapsed_statement,
		elapsed_expression,
		100 * (elapsed_expression - elapsed_statement) / elapsed_statement
	);
	return 0;
}