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/compiler/nir/nir_search.c

@@ -144,7 +144,6 @@ nir_op_matches_search_op(nir_op nop, uint16_t sop)
    MATCH_ICONV_CASE(i2i)
    MATCH_FCONV_CASE(b2f)
    MATCH_ICONV_CASE(b2i)
-   MATCH_BCONV_CASE(i2b)
    MATCH_BCONV_CASE(f2b)
    default:
       unreachable("Invalid nir_search_op");
@@ -187,7 +186,6 @@ nir_search_op_for_nir_op(nir_op nop)
    MATCH_ICONV_CASE(i2i)
    MATCH_FCONV_CASE(b2f)
    MATCH_ICONV_CASE(b2i)
-   MATCH_BCONV_CASE(i2b)
    MATCH_BCONV_CASE(f2b)
    default:
       return nop;
@@ -241,7 +239,6 @@ nir_op_for_search_op(uint16_t sop, unsigned bit_size)
    RET_ICONV_CASE(i2i)
    RET_FCONV_CASE(b2f)
    RET_ICONV_CASE(b2i)
-   RET_BCONV_CASE(i2b)
    RET_BCONV_CASE(f2b)
    default:
       unreachable("Invalid nir_search_op");
@@ -621,7 +618,6 @@ UNUSED static void dump_value(const nir_algebraic_table *table, const nir_search
       CASE(f2b)
       CASE(b2f)
       CASE(b2i)
-      CASE(i2b)
       CASE(i2i)
       CASE(f2i)
       CASE(i2f)