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i965: Use LZD to implement nir_op_find_lsb on Gen < 7

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v2: Rebase on changes to previous two patches.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
This commit is contained in:
Ian Romanick
2016-06-22 13:12:26 -07:00
parent c2019c6c26
commit 3e7cebc8da
2 changed files with 45 additions and 3 deletions
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22
src/mesa/drivers/dri/i965/brw_fs_nir.cpp
View File

@@ -1387,7 +1387,27 @@ fs_visitor::nir_emit_alu(const fs_builder &bld, nir_alu_instr *instr)
case nir_op_find_lsb:
assert(nir_dest_bit_size(instr->dest.dest) < 64);
bld.FBL(result, op[0]);
if (devinfo->gen < 7) {
fs_reg temp = vgrf(glsl_type::int_type);
/* (x & -x) generates a value that consists of only the LSB of x.
* For all powers of 2, findMSB(y) == findLSB(y).
*/
fs_reg src = retype(op[0], BRW_REGISTER_TYPE_D);
fs_reg negated_src = src;
/* One must be negated, and the other must be non-negated. It
* doesn't matter which is which.
*/
negated_src.negate = true;
src.negate = false;
bld.AND(temp, src, negated_src);
emit_find_msb_using_lzd(bld, result, temp, false);
} else {
bld.FBL(result, op[0]);
}
break;
case nir_op_ubitfield_extract:

26
src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
View File

@@ -1535,9 +1535,31 @@ vec4_visitor::nir_emit_alu(nir_alu_instr *instr)
break;
}
case nir_op_find_lsb:
emit(FBL(dst, op[0]));
case nir_op_find_lsb: {
vec4_builder bld = vec4_builder(this).at_end();
if (devinfo->gen < 7) {
dst_reg temp = bld.vgrf(BRW_REGISTER_TYPE_D);
/* (x & -x) generates a value that consists of only the LSB of x.
* For all powers of 2, findMSB(y) == findLSB(y).
*/
src_reg src = src_reg(retype(op[0], BRW_REGISTER_TYPE_D));
src_reg negated_src = src;
/* One must be negated, and the other must be non-negated. It
* doesn't matter which is which.
*/
negated_src.negate = true;
src.negate = false;
bld.AND(temp, src, negated_src);
emit_find_msb_using_lzd(bld, dst, src_reg(temp), false);
} else {
bld.FBL(dst, op[0]);
}
break;
}
case nir_op_ubitfield_extract:
case nir_op_ibitfield_extract: