Re-enable UBsan on AGC.

webrtc/modules/audio_processing/agc/legacy/digital_agc.c

Index: webrtc/modules/audio_processing/agc/legacy/digital_agc.c
diff --git a/webrtc/modules/audio_processing/agc/legacy/digital_agc.c b/webrtc/modules/audio_processing/agc/legacy/digital_agc.c
index 2ca967a4aae1a0d0a00758b4861a4838b1d11d46..8ad91278b0840e57a9ded287ef517e51f1d9fd25 100644
--- a/webrtc/modules/audio_processing/agc/legacy/digital_agc.c
+++ b/webrtc/modules/audio_processing/agc/legacy/digital_agc.c
@@ -187,14 +187,12 @@ int32_t WebRtcAgc_CalculateGainTable(int32_t* gainTable,       // Q16
     numFIX -= (int32_t)logApprox * diffGain;       // Q14
 
     // Calculate ratio
-    // Shift |numFIX| as much as possible.
-    // Ensure we avoid wrap-around in |den| as well.
-    if (numFIX > (den >> 8))  // |den| is Q8.

[minyue-webrtc, 2016/05/21 12:33:37]

Two problems were with this part

1. if |numFIX| is negative, it will take 196 and the shift can be too large

2. line 203/205 may overflow.

See my solution.

-    {
-      zeros = WebRtcSpl_NormW32(numFIX);
-    } else {
-      zeros = WebRtcSpl_NormW32(den) + 8;
-    }
+    // 1) Shift |numFIX| as much as possible. Since we later add |den| / 2 to
+    // |numFIX| before dividing |den| to round the ratio, we use |numFIX| *2 to
+    // calculate the bit for shifting.
+    // 2) Ensure we avoid wrap-around in |den| as well.
+    zeros = WEBRTC_SPL_MIN(WebRtcSpl_NormW32(numFIX * 2),

[peah-webrtc, 2016/05/23 04:59:37]

The norm computation is on some platforms fairly complex. It probably does not
matter that much, but it is likely faster to do instead do:
int64_t tmp64 = numFIX * 256;  // Q8.
if (tmp64 > den)  // |den| is Q8. 
{
 zeros = WebRtcSpl_NormW32(numFIX);
} else {
 zeros = WebRtcSpl_NormW32(den) + 8;
}

[peah-webrtc, 2016/05/23 04:59:37]

How do you know that numFIX * 2 does not overflow? Normalizing as
WebRtcSpl_NormW32(numFIX) which was done before seems safer.

Alternatively, if you want the norm to be one less than before, it is better to
compute zeros as
WebRtcSpl_NormW32(numFIX) - 1

[minyue-webrtc, 2016/05/23 07:40:48]

Good question, after a second thought, I see that |den| being too large can also
overflow. A better way is to deal with rounding in another way. See my new
patch.

On 2016/05/23 04:59:37, peah-webrtc wrote:

+                           WebRtcSpl_NormW32(den) + 8);
     numFIX *= 1 << zeros;  // Q(14+zeros)
 
     // Shift den so we end up in Qy1