perf tools: Cache register accesses for unwind processing

Caching registers value into an array. Got about 4% speed up
of perf_reg_value function for report command processing
dwarf unwind stacks.

Output from report over 1.5 GB data with DWARF unwind stacks:
(TODO fix perf diff)

current code:
5.84% perf perf [.] perf_reg_value
change:
1.94% perf perf [.] perf_reg_value

And little bit of overall speed up:
(perf stat -r 5 -e '{cycles,instructions}:u' ...)

current code:
310,298,611,754 cycles ( +- 0.33% )
439,669,689,341 instructions ( +- 0.03% )

188.656753166 seconds time elapsed ( +- 0.82% )

change:
291,315,329,878 cycles ( +- 0.22% )
391,763,485,304 instructions ( +- 0.03% )

180.742249687 seconds time elapsed ( +- 0.64% )

Acked-by: Namhyung Kim <[e-mail]>
Cc: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Corey Ashford <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jean Pihet <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Jiri Olsa <[e-mail]>

tools/perf/util/event.h

···
 #include "../perf.h"
 #include "map.h"
 #include "build-id.h"
+#include "perf_regs.h"
 
 struct mmap_event {
 	struct perf_event_header header;
···
 	u64 abi;
 	u64 mask;
 	u64 *regs;
+
+	/* Cached values/mask filled by first register access. */
+	u64 cache_regs[PERF_REGS_MAX];
+	u64 cache_mask;
 };
 
 struct stack_dump {

tools/perf/util/perf_regs.c

···
 #include <errno.h>
 #include "perf_regs.h"
+#include "event.h"
 
 int perf_reg_value(u64 *valp, struct regs_dump *regs, int id)
 {
 	int i, idx = 0;
 	u64 mask = regs->mask;
+
+	if (regs->cache_mask & (1 << id))
+		goto out;
 
 	if (!(mask & (1 << id)))
 		return -EINVAL;
···
 			idx++;
 	}
 
-	*valp = regs->regs[idx];
+	regs->cache_mask |= (1 << id);
+	regs->cache_regs[id] = regs->regs[idx];
+
+out:
+	*valp = regs->cache_regs[id];
 	return 0;
 }

tools/perf/util/perf_regs.h

···
 #define __PERF_REGS_H
 
 #include <linux/types.h>
-#include "event.h"
+
+struct regs_dump;
 
 #ifdef HAVE_PERF_REGS_SUPPORT
 #include <perf_regs.h>
···
 
 #else
 #define PERF_REGS_MASK	0
+#define PERF_REGS_MAX	0
 
 static inline const char *perf_reg_name(int id __maybe_unused)
 {