nir: Eliminate nir_op_i2b

There are a lot of optimizations in opt_algebraic that match ('ine', a,
0), but there are almost none that match i2b.  Instead of adding a huge
pile of additional patterns (including variations that include both ine
and i2b), always lower i2b to a != 0.

At this point in the series, it should be impossible for anything to
generate i2b, so there /should not/ be any changes.

The failing test on d3d12 is a pre-existing bug that is triggered by
this change.  I talked to Jesse about it, and, after some analysis, he
suggested just adding it to the list of known failures.

v2: Don't rematerialize i2b instructions in dxil_nir_lower_x2b.

v3: Don't rematerialize i2b instructions in zink_nir_algebraic.py.

v4: Fix zink-on-TGL CI failures by calling nir_opt_algebraic after
nir_lower_doubles makes progress.  The latter can generate b2i
instructions, but nir_lower_int64 can't handle them (anymore).

v5: Add back most of the hunk at line 2125 of nir_opt_algebraic.py. I
had accidentally removed the f2b(bf2(x)) optimization.

v6: Just eliminate the i2b instruction.

v7: Remove missed i2b32 in midgard_compile.c. Remove (now unused)
emit_alu_i2orf2_b1 function from sfn_instr_alu.cpp. Previously this
function was still used. 🤷

No shader-db changes on any Intel platform.

All Intel platforms had similar results. (Ice Lake shown)
Instructions in all programs: 141165875 -> 141165873 (-0.0%)
Instructions helped: 2

Cycles in all programs: 9098956382 -> 9098956350 (-0.0%)
Cycles helped: 2

The two Vulkan shaders are helped because of the "new" (('b2i32',
('ine', ('ubfe', a, b, 1), 0)), ('ubfe', a, b, 1)) algebraic pattern.

Acked-by: Jesse Natalie <jenatali@microsoft.com> [earlier version]
Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Tested-by: Daniel Schürmann <daniel@schuermann.dev> [earlier version]
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15121>

src/intel/compiler/brw_vec4_nir.cpp

@@ -1576,10 +1576,6 @@ vec4_visitor::nir_emit_alu(nir_alu_instr *instr)
       }
       break;
 
-   case nir_op_i2b32:
-      emit(CMP(dst, op[0], brw_imm_d(0), BRW_CONDITIONAL_NZ));
-      break;
-
    case nir_op_unpack_half_2x16_split_x:
    case nir_op_unpack_half_2x16_split_y:
    case nir_op_pack_half_2x16_split: