regressions: Add stupid fast-path benchmark for fences.

This is far from comprehensive but needed for some upcoming
tests.

regressions/ck_pr/benchmark/Makefile

@@ -1,6 +1,9 @@
 .PHONY: clean
 
-all: ck_pr_cas_64 ck_pr_fas_64 ck_pr_cas_64_2
+all: ck_pr_cas_64 ck_pr_fas_64 ck_pr_cas_64_2 fp
+
+fp: fp.c
+	$(CC) $(CFLAGS) -o fp fp.c
 
 ck_pr_cas_64_2: ck_pr_cas_64_2.c
 	$(CC) $(CFLAGS) -o ck_pr_cas_64_2 ck_pr_cas_64_2.c -lm

regressions/ck_pr/benchmark/fp.c

@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <inttypes.h>
+#include <stdint.h>
+
+#include "../../common.h"
+
+#ifndef IR
+#define IR 3000000
+#endif /* IR */
+
+static int a CK_CC_CACHELINE;
+static int b CK_CC_CACHELINE;
+
+int
+main(void)
+{
+	uint64_t s, e;
+	unsigned int i;
+
+	s = rdtsc();
+	for (i = 0; i < IR; i++) {
+		ck_pr_load_int(&a);
+		ck_pr_fence_strict_load();
+		ck_pr_load_int(&b);
+	}
+	e = rdtsc();
+	printf("fence_load: %" PRIu64 "\n", (e - s) / IR);
+
+	s = rdtsc();
+	for (i = 0; i < IR; i++) {
+		ck_pr_store_int(&a, 0);
+		ck_pr_fence_strict_store();
+		ck_pr_load_int(&b);
+	}
+	e = rdtsc();
+	printf("fence_store: %" PRIu64 "\n", (e - s) / IR);
+
+	s = rdtsc();
+	for (i = 0; i < IR; i++) {
+		ck_pr_store_int(&a, 0);
+		ck_pr_fence_strict_memory();
+		ck_pr_load_int(&b);
+	}
+	e = rdtsc();
+	printf("fence_memory: %" PRIu64 "\n", (e - s) / IR);
+
+	s = rdtsc();
+	for (i = 0; i < IR; i++) {
+		ck_pr_store_int(&a, 0);
+		ck_pr_faa_int(&a, 0);
+		ck_pr_load_int(&b);
+	}
+	e = rdtsc();
+	printf("atomic: %" PRIu64 "\n", (e - s) / IR);
+	return 0;
+}