i965: fix invalid memory write

i965: fix invalid memory write

I noticed some heap corruption running virgl tests, and valgrind
helped me to track it down to the following error:

==29272== Invalid write of size 4
==29272==    at 0x90283D4: push_loop_stack (brw_eu_emit.c:1307)
==29272==    by 0x9029A7D: brw_DO (brw_eu_emit.c:1750)
==29272==    by 0x90554B0: fs_generator::generate_code(cfg_t const*, int) (brw_fs_generator.cpp:1999)
==29272==    by 0x904491F: brw_compile_fs (brw_fs.cpp:5685)
==29272==    by 0x8FC5DC5: brw_codegen_wm_prog (brw_wm.c:137)
==29272==    by 0x8FC7663: brw_fs_precompile (brw_wm.c:638)
==29272==    by 0x8FA4040: brw_shader_precompile(gl_context*, gl_shader_program*) (brw_link.cpp:51)
==29272==    by 0x8FA4A9A: brw_link_shader (brw_link.cpp:260)
==29272==    by 0x8DEF751: _mesa_glsl_link_shader (ir_to_mesa.cpp:3006)
==29272==    by 0x8C84325: _mesa_link_program (shaderapi.c:1042)
==29272==    by 0x8C851D7: _mesa_LinkProgram (shaderapi.c:1515)
==29272==    by 0x4E4B8E8: add_shader_program (vrend_renderer.c:880)
==29272==  Address 0xf2f3cb0 is 0 bytes after a block of size 112 alloc'd
==29272==    at 0x4C2AA98: calloc (vg_replace_malloc.c:711)
==29272==    by 0x8ED11F7: ralloc_size (ralloc.c:113)
==29272==    by 0x8ED1282: rzalloc_size (ralloc.c:134)
==29272==    by 0x8ED14C0: rzalloc_array_size (ralloc.c:196)
==29272==    by 0x9019C7B: brw_init_codegen (brw_eu.c:291)
==29272==    by 0x904F565: fs_generator::fs_generator(brw_compiler const*, void*, void*, void const*, brw_stage_prog_data*, unsigned int, bool, gl_shader_stage) (brw_fs_generator.cpp:124)
==29272==    by 0x9044883: brw_compile_fs (brw_fs.cpp:5675)
==29272==    by 0x8FC5DC5: brw_codegen_wm_prog (brw_wm.c:137)
==29272==    by 0x8FC7663: brw_fs_precompile (brw_wm.c:638)
==29272==    by 0x8FA4040: brw_shader_precompile(gl_context*, gl_shader_program*) (brw_link.cpp:51)
==29272==    by 0x8FA4A9A: brw_link_shader (brw_link.cpp:260)
==29272==    by 0x8DEF751: _mesa_glsl_link_shader (ir_to_mesa.cpp:3006)

if_depth_in_loop is an array of size p->loop_stack_array_size, and
push_loop_stack() will access if_depth_in_loop[p->loop_stack_depth+1],
thus the condition to grow the array should be
p->loop_stack_array_size <= (p->loop_stack_depth + 1) (it's currently
off by 2...)

This can be reproduced by running the following test with virgl test
server:
LIBGL_ALWAYS_SOFTWARE=y GALLIUM_DRIVER=virpipe bin/shader_runner
./tests/shaders/glsl-fs-unroll-explosion.shader_test -auto

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>