nir: Add lowering from ibitfield_extract/ubitfield_extract to shifts.

V3D doesn't have opcodes for ibfe/ubfe, so we need to lower similarly to
glsl/lower_instructions.cpp.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/compiler/nir/nir.h

@@ -1903,7 +1903,10 @@ typedef struct nir_shader_compiler_options {
    bool lower_fsqrt;
    bool lower_fmod32;
    bool lower_fmod64;
+   /** Lowers ibitfield_extract/ubitfield_extract to ibfe/ubfe. */
    bool lower_bitfield_extract;
+   /** Lowers ibitfield_extract/ubitfield_extract to bfm, compares, shifts. */
+   bool lower_bitfield_extract_to_shifts;
    /** Lowers bitfield_insert to bfi/bfm */
    bool lower_bitfield_insert;
    /** Lowers bitfield_insert to bfm, compares, and shifts. */

src/compiler/nir/nir_opt_algebraic.py

@@ -539,6 +539,22 @@ optimizations = [
               ('ubfe', 'value', 'offset', 'bits')),
     'options->lower_bitfield_extract'),
 
+   (('ibitfield_extract', 'value', 'offset', 'bits'),
+    ('bcsel', ('ieq', 0, 'bits'),
+     0,
+     ('ishr',
+       ('ishl', 'value', ('isub', ('isub', 32, 'bits'), 'offset')),
+       ('isub', 32, 'bits'))),
+    'options->lower_bitfield_extract_to_shifts'),
+
+   (('ubitfield_extract', 'value', 'offset', 'bits'),
+    ('iand',
+     ('ushr', 'value', 'offset'),
+     ('bcsel', ('ieq', 'bits', 32),
+      0xffffffff,
+      ('bfm', 'bits', 0))),
+    'options->lower_bitfield_extract_to_shifts'),
+
    (('extract_i8', a, 'b@32'),
     ('ishr', ('ishl', a, ('imul', ('isub', 3, b), 8)), 24),
     'options->lower_extract_byte'),