nir: Add opcodes to extract bytes or words.

The uint versions zero extend while the int versions sign extend.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>

src/compiler/nir/nir.h

@@ -1471,6 +1471,9 @@ typedef struct nir_shader_compiler_options {
    bool lower_pack_half_2x16;
    bool lower_unpack_half_2x16;
 
+   bool lower_extract_byte;
+   bool lower_extract_word;
+
    /**
     * Does the driver support real 32-bit integers?  (Otherwise, integers
     * are simulated by floats.)

src/compiler/nir/nir_opcodes.py

@@ -536,6 +536,15 @@ dst.x = src0.x;
 dst.y = src1.x;
 """)
 
+# Byte extraction
+binop("extract_u8", tuint, "", "(uint8_t)(src0 >> (src1 * 8))")
+binop("extract_i8", tint, "", "(int8_t)(src0 >> (src1 * 8))")
+
+# Word extraction
+binop("extract_u16", tuint, "", "(uint16_t)(src0 >> (src1 * 16))")
+binop("extract_i16", tint, "", "(int16_t)(src0 >> (src1 * 16))")
+
+
 def triop(name, ty, const_expr):
    opcode(name, 0, ty, [0, 0, 0], [ty, ty, ty], "", const_expr)
 def triop_horiz(name, output_size, src1_size, src2_size, src3_size, const_expr):

src/compiler/nir/nir_opt_algebraic.py

@@ -242,6 +242,22 @@ optimizations = [
     ('bcsel', ('ult', 31, 'bits'), 'value',
               ('ubfe', 'value', 'offset', 'bits')),
     'options->lower_bitfield_extract'),
+
+   (('extract_i8', a, b),
+    ('ishr', ('ishl', a, ('imul', ('isub', 3, b), 8)), 24),
+    'options->lower_extract_byte'),
+
+   (('extract_u8', a, b),
+    ('iand', ('ushr', a, ('imul', b, 8)), 0xff),
+    'options->lower_extract_byte'),
+
+   (('extract_i16', a, b),
+    ('ishr', ('ishl', a, ('imul', ('isub', 1, b), 16)), 16),
+    'options->lower_extract_word'),
+
+   (('extract_u16', a, b),
+    ('iand', ('ushr', a, ('imul', b, 16)), 0xffff),
+    'options->lower_extract_word'),
 ]
 
 # Add optimizations to handle the case where the result of a ternary is