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nir/lower_double_ops: lower trunc()

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At least i965 hardware does not have native support for truncating doubles.

v2:
  - Simplified the implementation significantly.
  - Fixed the else branch, that was not doing what we wanted.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
This commit is contained in:
Iago Toral Quiroga
2016-01-04 12:52:14 +01:00
committed by Samuel Iglesias Gonsálvez
parent 2ea3649c63
commit 5fab3d178b
2 changed files with 61 additions and 0 deletions
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1
src/compiler/nir/nir.h
View File

@@ -2417,6 +2417,7 @@ typedef enum {
nir_lower_drcp = (1 << 0),
nir_lower_dsqrt = (1 << 1),
nir_lower_drsq = (1 << 2),
nir_lower_dtrunc = (1 << 3),
} nir_lower_doubles_options;
void nir_lower_doubles(nir_shader *shader, nir_lower_doubles_options options);

60
src/compiler/nir/nir_lower_double_ops.c
View File

@@ -299,6 +299,58 @@ lower_sqrt_rsq(nir_builder *b, nir_ssa_def *src, bool sqrt)
return res;
}
static nir_ssa_def *
lower_trunc(nir_builder *b, nir_ssa_def *src)
{
nir_ssa_def *unbiased_exp = nir_isub(b, get_exponent(b, src),
nir_imm_int(b, 1023));
nir_ssa_def *frac_bits = nir_isub(b, nir_imm_int(b, 52), unbiased_exp);
/*
* Decide the operation to apply depending on the unbiased exponent:
*
* if (unbiased_exp < 0)
* return 0
* else if (unbiased_exp > 52)
* return src
* else
* return src & (~0 << frac_bits)
*
* Notice that the else branch is a 64-bit integer operation that we need
* to implement in terms of 32-bit integer arithmetics (at least until we
* support 64-bit integer arithmetics).
*/
/* Compute "~0 << frac_bits" in terms of hi/lo 32-bit integer math */
nir_ssa_def *mask_lo =
nir_bcsel(b,
nir_ige(b, frac_bits, nir_imm_int(b, 32)),
nir_imm_int(b, 0),
nir_ishl(b, nir_imm_int(b, ~0), frac_bits));
nir_ssa_def *mask_hi =
nir_bcsel(b,
nir_ilt(b, frac_bits, nir_imm_int(b, 33)),
nir_imm_int(b, ~0),
nir_ishl(b,
nir_imm_int(b, ~0),
nir_isub(b, frac_bits, nir_imm_int(b, 32))));
nir_ssa_def *src_lo = nir_unpack_double_2x32_split_x(b, src);
nir_ssa_def *src_hi = nir_unpack_double_2x32_split_y(b, src);
return
nir_bcsel(b,
nir_ilt(b, unbiased_exp, nir_imm_int(b, 0)),
nir_imm_double(b, 0.0),
nir_bcsel(b, nir_ige(b, unbiased_exp, nir_imm_int(b, 53)),
src,
nir_pack_double_2x32_split(b,
nir_iand(b, mask_lo, src_lo),
nir_iand(b, mask_hi, src_hi))));
}
static void
lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options options)
{
@@ -322,6 +374,11 @@ lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options options)
return;
break;
case nir_op_ftrunc:
if (!(options & nir_lower_dtrunc))
return;
break;
default:
return;
}
@@ -345,6 +402,9 @@ lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options options)
case nir_op_frsq:
result = lower_sqrt_rsq(&bld, src, false);
break;
case nir_op_ftrunc:
result = lower_trunc(&bld, src);
break;
default:
unreachable("unhandled opcode");
}