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From: "trippels at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/60902] ffmpeg built with gcc 4.9 RC produces incorrect flac playback code
Date: Sun, 20 Apr 2014 11:53:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60902

--- Comment #11 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
OK I'm down to one function from ./libavcodec/flacdec.c:

208 __attribute__ ((optimize(0)))
209 static int decode_residuals(FLACContext *s, int32_t *decoded, int
pred_order)
210 {
211     int i, tmp, partition, method_type, rice_order;
212     int rice_bits, rice_esc;
213     int samples;
214
215     method_type = get_bits(&s->gb, 2);
216     if (method_type > 1) {
217         av_log(s->avctx, AV_LOG_ERROR, "illegal residual coding method
%d\n",
218                method_type);
219         return AVERROR_INVALIDDATA;
220     }
221
222     rice_order = get_bits(&s->gb, 4);
223
224     samples= s->blocksize >> rice_order;
225     if (samples << rice_order != s->blocksize) {
226         av_log(s->avctx, AV_LOG_ERROR, "invalid rice order: %i blocksize
%i\n",
227                rice_order, s->blocksize);
228         return AVERROR_INVALIDDATA;
229     }
230
231     if (pred_order > samples) {
232         av_log(s->avctx, AV_LOG_ERROR, "invalid predictor order: %i >
%i\n",
233                pred_order, samples);
234         return AVERROR_INVALIDDATA;
235     }
236
237     rice_bits = 4 + method_type;
238     rice_esc  = (1 << rice_bits) - 1;
239
240     decoded += pred_order;
241     i= pred_order;
242     for (partition = 0; partition < (1 << rice_order); partition++) {
243         tmp = get_bits(&s->gb, rice_bits);
244         if (tmp == rice_esc) {
245             tmp = get_bits(&s->gb, 5);
246             for (; i < samples; i++)
247                 *decoded++ = get_sbits_long(&s->gb, tmp);
248         } else {
249             for (; i < samples; i++) {
250                 *decoded++ = get_sr_golomb_flac(&s->gb, tmp, INT_MAX, 0);
251             }
252         }
253         i= 0;
254     }
255
256     return 0;
257 }
258

Without __attribute__ ((optimize(0))) it gets miscompiled.