I have hit this using v7.0.2 too.

Can you provide a program to test with?

Does it also happen with a debug build?  Can you print some of the vars near the failure point?

Unfortunately, I can not provide a simple test program to test with.

However, here are two variables that I printed out earlier, when I hit it again, I will provide more local variables.  These are in the bottom frame:

  x0 == -4376.
  y0 == -2186.
  dx ==  1093.

Debugger didn't want to print the variable 'i'. (No symbol "i" in current context)

Here is more debug info:

#0  flat_8A8B8G8R_line (ctx=0x3f800000, vert0=0x385, vert1=0x2aaaafe9f448) at ../../src/mesa/swrast/s_linetemp.h:376
#1  0x00002ac32202a2ac in _swsetup_render_line_tri (ctx=0x1fd8420, e0=901, e1=2951345224, e2=4294966395, facing=4294967295) at swrast_setup/ss_triangle.c:88
#2  0x00002ac32202ea25 in triangle_unfilled_rgba (ctx=0xffffffffffffee58, e0=4294965494, e1=4294962776, e2=4) at swrast_setup/ss_tritmp.h:153
#3  0x00002ac321f9427b in _tnl_render_poly_elts (ctx=0x1fd8420, start=1, count=4, flags=3) at tnl/t_vb_rendertmp.h:284
#4  0x00002ac321f94762 in _tnl_RenderClippedPolygon (ctx=0xffffffffffffee58, elts=0x385, n=2951345224) at tnl/t_vb_render.c:244
#5  0x00002ac321f8eb7e in clip_quad_4 (ctx=0x1fd8420, v0=901, v1=2951345224, v2=4294966395, v3=3, mask=64 '@') at tnl/t_vb_cliptmp.h:281
#6  0x00002ac321f90b27 in clip_render_quads_verts (ctx=0x1fd8420, start=3, count=4, flags=4294966395) at tnl/t_vb_rendertmp.h:334
#7  0x00002ac321f948c5 in run_render (ctx=0x1fd8420, stage=0x385) at tnl/t_vb_render.c:320
#8  0x00002ac321f8b57a in _tnl_run_pipeline (ctx=0x1fd8420) at tnl/t_pipeline.c:158
#9  0x00002ac321f8ba8f in _tnl_draw_prims (ctx=0x1fd8420, arrays=0x202b558, prim=0x7fff9abdb360, nr_prims=1, ib=0x0, min_index=2951345224, max_index=901) at tnl/t_draw.c:402
#10 0x00002ac321f7e766 in vbo_exec_DrawArrays (mode=7, start=0, count=4) at vbo/vbo_exec_array.c:259


(gdb) p x0
$185 = -4520
(gdb) p y0
$186 = -1802
(gdb) p dy
$187 = 901
(gdb) p i
No symbol "i" in current context.
(gdb) p errorInc
$188 = 0
(gdb) p dx
$189 = 4
(gdb) p error
$190 = -901
(gdb) p errorDec
$192 = -1802
(gdb) p span
$195 = {
  x = -1698836480, 
  y = 32767, 
  end = 901, 
  writeAll = 0 '\0', 
  primitive = 6913, 
  facing = 0, 
  interpMask = 0, 
  attrStart = {{1.53400143e-41, 1.47715355e-38, 0, 1}, {1.53400143e-41, 0, 1.84971397e-42, 1.67952199e-36}, {0, -7.84429148e-23, 4.59163468e-41, 4.84620802e-18}, {1.53400143e-41, 1.67952199e-36, 0, 1.67952486e-36}, {0, 1.67952199e-36, 0, 1.82010027e-22}, {1.53400143e-41, -7.84435206e-23, 4.59163468e-41, 4.76441478e-44}, {0, -7.850461e-23, 4.59163468e-41, 0}, {0, 0, 0, 1.44805756e-22}, {1.53400143e-41, 1.34358515e-38, 2.3509887e-38, 1.34358515e-38}, {0, -7.84435206e-23, 4.59163468e-41, 1.64045994e-27}, {1.53400143e-41, 2.34787369e-15, 1.40129846e-45, 1.34358515e-38}, {0, -7.84437226e-23, 4.59163468e-41, 2.94091191e-24}, {1.53400143e-41, 1.34358515e-38, 0, -7.84450352e-23}, {4.59163468e-41, -7.84455401e-23, 4.59163468e-41, 1.20350345e-16}, {1.53400143e-41, -7.84462469e-23, 4.59163468e-41, 1.82010027e-22}, {1.53400143e-41, -7.84444294e-23, 4.59163468e-41, 4.76441478e-44}, {0, -7.850461e-23, 4.59163468e-41, 0}, {0, 0, 0, 1.44805756e-22}, {1.53400143e-41, 1.47715355e-38, 0, 1.65527104e-15}, {1.53400143e-41, 0, 0, 2.90652619e-38}}, 
  attrStepX = {{0, -7.84447323e-23, 4.59163468e-41, 0}, {1.53400143e-41, 2.90652619e-38, 0, 2.90653068e-38}, {0, 0, 0, -7.84451362e-23}, {4.59163468e-41, -7.84450352e-23, 4.59163468e-41, 1.43936097e-23}, {1.53400143e-41, -7.850461e-23, 4.59163468e-41, 0}, {3.57331108e-43, 1.34461146e-38, 0, -7.84451362e-23}, {4.59163468e-41, 1.37874092e-38, 2.3509887e-38, 1.37874092e-38}, {0, -7.84453382e-23, 4.59163468e-41, 1.64045994e-27}, {1.53400143e-41, 2.34787369e-15, 1.40129846e-45, 1.37874092e-38}, {0, -7.84455401e-23, 4.59163468e-41, 2.94091191e-24}, {1.53400143e-41, 1.37874092e-38, 0, -7.84468528e-23}, {4.59163468e-41, -7.84473576e-23, 4.59163468e-41, 1.20350345e-16}, {1.53400143e-41, -7.84480645e-23, 4.59163468e-41, 1.82010027e-22}, {1.53400143e-41, -7.84462469e-23, 4.59163468e-41, 4.76441478e-44}, {0, -7.850461e-23, 4.59163468e-41, 0}, {0, 0, 0, 1.44805756e-22}, {1.53400143e-41, 1.47715355e-38, 0, 1.65527104e-15}, {1.53400143e-41, 2.80259693e-45, 2.80259693e-45, 1.67815881e-36}, {0, -7.84465498e-23, 4.59163468e-41, 4.84620802e-18}, {1.53400143e-41, 1.67815881e-36, 0, 1.67816168e-36}}, 
  attrStepY = {{0, 0, 0, 0}, {4.59163468e-41, -7.84468528e-23, 4.59163468e-41, 1.43936097e-23}, {1.53400143e-41, -7.850461e-23, 4.59163468e-41, 0}, {3.57331108e-43, 1.36543587e-38, 0, -7.84469537e-23}, {4.59163468e-41, 1.39233015e-38, 2.3509887e-38, 1.39233015e-38}, {0, -7.84471557e-23, 4.59163468e-41, 1.64045994e-27}, {1.53400143e-41, 2.34787369e-15, 1.40129846e-45, 1.39233015e-38}, {0, -7.84473576e-23, 4.59163468e-41, 2.94091191e-24}, {1.53400143e-41, 1.39233015e-38, 0, -7.84486703e-23}, {4.59163468e-41, -7.84491752e-23, 4.59163468e-41, 1.20350345e-16}, {1.53400143e-41, -7.8449882e-23, 4.59163468e-41, 1.82010027e-22}, {1.53400143e-41, -7.84480645e-23, 4.59163468e-41, 4.76441478e-44}, {0, -7.850461e-23, 4.59163468e-41, 0}, {0, 0, 0, 1.44805756e-22}, {1.53400143e-41, 1.47715355e-38, 0, 1.65527104e-15}, {1.53400143e-41, 0, 0, 2.9134004e-38}, {0, -7.84483674e-23, 4.59163468e-41, 4.84620802e-18}, {1.53400143e-41, 2.9134004e-38, 0, 2.91340488e-38}, {0, 0, 0, -7.84487713e-23}, {4.59163468e-41, -7.84486703e-23, 4.59163468e-41, 1.43936097e-23}}, 
  red = 10947, 
  redStep = -1698836480, 
  green = 32767, 
  greenStep = 0, 
  blue = 255, 
  blueStep = 10376348, 
  alpha = 0, 
  alphaStep = 33391648, 
  specRed = 0, 
  specRedStep = 33585232, 
  specGreen = 0, 
  specGreenStep = 38054752, 
  specBlue = 0, 
  specBlueStep = 38055456, 
  index = 0, 
  indexStep = 38055456, 
  z = 0, 
  zStep = 33391648, 
  intTex = {0, 570362374}, 
  intTexStep = {10947, -1698845264}, 
  arrayMask = 2048, 
  array = 0x2036f80
}

Are you still able to reproduce this on more recent versions of Mesa?  This code has seen a lot of change in the last two years.

I am no longer working on the product with which I originally hit this bug and thus cannot offer any more information about this issue that I had hit.

Okay.  I'll go ahead and close the bug.