I noticed ROUND support in today's mesa git so I decided to give mlaa a try however when starting HoN with pp_jimenezmlaa set it crash with: 

r300_state_derived.c:795:r300_merge_textures_and_samplers: Assertion `(tex->tex_offset & 0x1f) == 0' failed.

Program received signal SIGTRAP, Trace/breakpoint trap.
0xa1850c39 in _debug_assert_fail (expr=0xa1fcd081 "(tex->tex_offset & 0x1f) == 0", file=0xa1fccb14 "r300_state_derived.c", line=795, 
    function=0xa1fcd0a0 "r300_merge_textures_and_samplers") at util/u_debug.c:282
282	      os_abort();
(gdb) bt full
#0  0xa1850c39 in _debug_assert_fail (expr=0xa1fcd081 "(tex->tex_offset & 0x1f) == 0", file=0xa1fccb14 "r300_state_derived.c", line=795, 
    function=0xa1fcd0a0 "r300_merge_textures_and_samplers") at util/u_debug.c:282
No locals.
#1  0xa15bd6fa in r300_merge_textures_and_samplers (r300=0x936fc98) at r300_state_derived.c:795
        state = 0x9375480
        texstate = 0x9375510
        sampler = 0xa0ef470
        view = 0x15de3658
        tex = 0x9377e98
        base_level = 0
        min_level = 0
        level_count = 0
        i = 0
        j = 2721371740
        size = 2
        count = 1
        has_us_format = 0 '\000'
        __FUNCTION__ = "r300_merge_textures_and_samplers"
#2  0xa15bdd6c in r300_update_derived_state (r300=0x936fc98) at r300_state_derived.c:1006
No locals.
#3  0xa15b1fcc in r300_draw_vbo (pipe=0x936fc98, dinfo=0xbfffed44) at r300_render.c:779
        r300 = 0x936fc98
        info = {indexed = 0 '\000', mode = 7, start = 0, count = 4, start_instance = 0, instance_count = 1, index_bias = 0, 
          min_index = 0, max_index = 3, primitive_restart = 0 '\000', restart_index = 0}
#4  0xa185870c in util_draw_arrays (pipe=0x936fc98, mode=7, start=0, count=4) at ./util/u_draw.h:63
        info = {indexed = 0 '\000', mode = 7, start = 0, count = 4, start_instance = 0, instance_count = 1, index_bias = 0, 
          min_index = 0, max_index = 3, primitive_restart = 0 '\000', restart_index = 0}
#5  0xa18587df in util_draw_vertex_buffer (pipe=0x936fc98, cso=0x9376cc8, vbuf=0x91fe1f0, offset=0, prim_type=7, num_verts=4, 
    num_attribs=2) at util/u_draw_quad.c:69
        vbuffer = {stride = 32, buffer_offset = 0, buffer = 0x91fe1f0}
        __FUNCTION__ = "util_draw_vertex_buffer"
#6  0xa182fb12 in pp_filter_draw (p=0x936fb40) at postprocess/pp_run.c:170
No locals.
#7  0xa182ead5 in pp_jimenezmlaa_run (ppq=0x936fab8, in=0x937a4a8, out=0x15af7c18, n=0, iscolor=false) at postprocess/pp_mlaa.c:133
        p = 0x936fb40
        mstencil = {depth = {enabled = 0, writemask = 0, func = 0}, stencil = {{enabled = 1, func = 7, fail_op = 0, zpass_op = 2, 
              zfail_op = 0, valuemask = 255, writemask = 255}, {enabled = 0, func = 0, fail_op = 0, zpass_op = 0, zfail_op = 0, 
              valuemask = 0, writemask = 0}}, alpha = {enabled = 0, func = 0, ref_value = 0}}
        v_tmp = {reference = {count = 152853208}, format = 154598552, texture = 0x158c162, context = 0x3f800000, u = {tex = {
              first_layer = 0, last_layer = 16256, first_level = 0, last_level = 0}, buf = {first_element = 1065353216, 
              last_element = 0}}, swizzle_r = 0, swizzle_g = 0, swizzle_b = 0, swizzle_a = 0}
        arr = {0x33046c, 0x320, 0x500}
        w = 1280
        h = 800
        ref = {ref_value = "\001"}
#8  0xa182f2f7 in pp_jimenezmlaa (ppq=0x936fab8, in=0x937a4a8, out=0x15af7c18, n=0) at postprocess/pp_mlaa.c:295
No locals.
#9  0xa182f702 in pp_run (ppq=0x936fab8, in=0x937a4a8, out=0x15af7c18, indepth=0x15af7e90) at postprocess/pp_run.c:69
        i = 2709895702
#10 0xa1586469 in dri2_flush_drawable (dPriv=0x93792c0) at dri2.c:56
        ctx = 0x92690a8
        drawable = 0x93775c0
        ptex = 0x15af7c18
#11 0x0673e781 in dri2SwapBuffers (pdraw=0x9379218, target_msc=0, divisor=0, remainder=0) at dri2_glx.c:556
        gc = 0x9268fc0
        priv = 0x9379218
        dpyPriv = 0x8cd9df8
        psc = 0x8cda5e8
        pdp = 0x8c0c9c0
        ret = 0
#12 0x06707ec1 in glXSwapBuffers (dpy=0x8c0dd38, drawable=65011719) at glxcmds.c:805
        pdraw = 0x9379218
        gc = 0x9268fc0
        tag = 1065353216
        opcode = 7 '\a'
        req = 0x6622a4c
#13 0x0663daf4 in ?? () from /home/Paulie/HoN/vid_gl2-x86.so
No symbol table info available.
#14 0x0663db28 in ?? () from /home/Paulie/HoN/vid_gl2-x86.so
No symbol table info available.
#15 0x0077df6d in CVid::EndFrame() () from /home/Paulie/HoN/libk2-x86.so
No symbol table info available.
#16 0x002aeb17 in ?? () from /home/Paulie/HoN/libk2-x86.so
No symbol table info available.
#17 0x002aee6d in CHost::Execute() () from /home/Paulie/HoN/libk2-x86.so
No symbol table info available.
#18 0x08050997 in ?? ()
No symbol table info available.
#19 0x4b39c413 in __libc_start_main (main=0x805037a, argc=1, ubp_av=0xbffff364, init=0x8051c62, fini=0x8051c18, 
    rtld_fini=0x4b370dd0 <_dl_fini>, stack_end=0xbffff35c) at libc-start.c:226
        result = <optimized out>
        unwind_buf = {cancel_jmp_buf = {{jmp_buf = {1263579124, 0, 0, 0, -1490330656, 726228489}, mask_was_saved = 0}}, priv = {pad = {
              0x0, 0x0, 0x1, 0x804af84}, data = {prev = 0x0, cleanup = 0x0, canceltype = 1}}}
        not_first_call = <optimized out>
#20 0x0804afa5 in ?? ()
No symbol table info available.
Backtrace stopped: Not enough registers or memory available to unwind further

llvmpipe works fine. 
Setting vblank_mode to 0 fixes this issue.

Mesa: f0bfc0daa87578ce8b11383afb99dbf2d2630e23
Kernel: 3.0.4
GPU: RV530