[Bug tree-optimization/60902] [4.9/4.10 Regression] ffmpeg built with gcc 4.9 RC produces incorrect flac playback code

["trippels at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60902

--- Comment #20 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
All three testcases use the same inline function libavcodec/golomb.h:

314 /**
315  * read unsigned golomb rice code (jpegls).
316  */
317 static inline int get_ur_golomb_jpegls(GetBitContext *gb, int k, int limit,
318                                        int esc_len)
319 {
320     unsigned int buf;
321     int log;
322
323     OPEN_READER(re, gb);
324     UPDATE_CACHE(re, gb);
325     buf = GET_CACHE(re, gb);
326
327     log = av_log2(buf);
328
329     if (log - k >= 32 - MIN_CACHE_BITS + (MIN_CACHE_BITS == 32) &&
330         32 - log < limit) {
331         buf >>= log - k;
332         buf  += (30 - log) << k;
333         LAST_SKIP_BITS(re, gb, 32 + k - log);
334         CLOSE_READER(re, gb);
335
336         return buf;
337     } else {
338         int i;
339         for (i = 0; i < limit && SHOW_UBITS(re, gb, 1) == 0; i++) {
340             if (gb->size_in_bits <= re_index)
341                 return -1;
342             LAST_SKIP_BITS(re, gb, 1);
343             UPDATE_CACHE(re, gb);
344         }
345         SKIP_BITS(re, gb, 1);
346
347         if (i < limit - 1) {
348             if (k) {
349                 buf = SHOW_UBITS(re, gb, k);
350                 LAST_SKIP_BITS(re, gb, k);
351             } else {
352                 buf = 0;
353             }
354
355             CLOSE_READER(re, gb);
356             return buf + (i << k);
357         } else if (i == limit - 1) {
358             buf = SHOW_UBITS(re, gb, esc_len);
359             LAST_SKIP_BITS(re, gb, esc_len);
360             CLOSE_READER(re, gb);
361
362             return buf + 1;
363         } else
364             return -1;
365     }
366 }

And indeed adding __attribute__ ((optimize(0))) to it "fixes" all three
testcases. 
The function looks suspicious and I'm not sure if the code is valid.