libavcodec/pngdec.c:224: error: Uninitialized Value
  The value read from g was never initialized.

libavcodec/pngdec.c:224:13: 
222.         } else {
223. #define OP_SUB(x, s, l) x + s
224.             UNROLL_FILTER(OP_SUB);
                 ^
225.         }
226.         break;

static void png_filter_row(PNGDSPContext *dsp, uint8_t *dst, int filter_type,
                           uint8_t *src, uint8_t *last, int size, int bpp)
{
    int i, p, r, g, b, a;
    switch (filter_type) {
    case PNG_FILTER_VALUE_NONE:
        memcpy(dst, src, size);
        break;
    case PNG_FILTER_VALUE_SUB:
        for (i = 0; i < bpp; i++)
            dst[i] = src[i];
        if (bpp == 4) {
            p = *(int *)dst;
            for (; i < size; i += bpp) {
                int s = *(int *)(src + i);
                p = ((s & 0x7f7f7f7f) + (p & 0x7f7f7f7f)) ^ ((s ^ p) & 0x80808080);
                *(int *)(dst + i) = p;
            }
        } else {
#define OP_SUB(x, s, l) x + s
            UNROLL_FILTER(OP_SUB);
        }
        break;
    case PNG_FILTER_VALUE_UP:
        dsp->add_bytes_l2(dst, src, last, size);
        break;
    case PNG_FILTER_VALUE_AVG:
        for (i = 0; i < bpp; i++) {
            p      = (last[i] >> 1);
            dst[i] = p + src[i];
        }
#define OP_AVG(x, s, l) (((x + l) >> 1) + s) & 0xff
        UNROLL_FILTER(OP_AVG);
        break;
    case PNG_FILTER_VALUE_PAETH:
        for (i = 0; i < bpp; i++) {
            p      = last[i];
            dst[i] = p + src[i];
        }
        if (bpp > 1 && size > 4) {
            int w = bpp == 4 ? size : size - 3;
            dsp->add_paeth_prediction(dst + i, src + i, last + i, w - i, bpp);
            i = w;
        }
        ff_add_png_paeth_prediction(dst + i, src + i, last + i, size - i, bpp);
        break;
    }
}
['static void png_filter_row(PNGDSPContext *dsp, uint8_t *dst, int filter_type,\n                           uint8_t *src, uint8_t *last, int size, int bpp)\n{\n    int i, p, r, g, b, a;\n    switch (filter_type) {\n    case PNG_FILTER_VALUE_NONE:\n        memcpy(dst, src, size);\n        break;\n    case PNG_FILTER_VALUE_SUB:\n        for (i = 0; i < bpp; i++)\n            dst[i] = src[i];\n        if (bpp == 4) {\n            p = *(int *)dst;\n            for (; i < size; i += bpp) {\n                int s = *(int *)(src + i);\n                p = ((s & 0x7f7f7f7f) + (p & 0x7f7f7f7f)) ^ ((s ^ p) & 0x80808080);\n                *(int *)(dst + i) = p;\n            }\n        } else {\n#define OP_SUB(x, s, l) x + s\n            UNROLL_FILTER(OP_SUB);\n        }\n        break;\n    case PNG_FILTER_VALUE_UP:\n        dsp->add_bytes_l2(dst, src, last, size);\n        break;\n    case PNG_FILTER_VALUE_AVG:\n        for (i = 0; i < bpp; i++) {\n            p      = (last[i] >> 1);\n            dst[i] = p + src[i];\n        }\n#define OP_AVG(x, s, l) (((x + l) >> 1) + s) & 0xff\n        UNROLL_FILTER(OP_AVG);\n        break;\n    case PNG_FILTER_VALUE_PAETH:\n        for (i = 0; i < bpp; i++) {\n            p      = last[i];\n            dst[i] = p + src[i];\n        }\n        if (bpp > 1 && size > 4) {\n            int w = bpp == 4 ? size : size - 3;\n            dsp->add_paeth_prediction(dst + i, src + i, last + i, w - i, bpp);\n            i = w;\n        }\n        ff_add_png_paeth_prediction(dst + i, src + i, last + i, size - i, bpp);\n        break;\n    }\n}']