nir/lower_double_ops: lower trunc()
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>
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committed by
Samuel Iglesias Gonsálvez

parent
2ea3649c63
commit
5fab3d178b
@@ -2417,6 +2417,7 @@ typedef enum {
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nir_lower_drcp = (1 << 0),
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nir_lower_dsqrt = (1 << 1),
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nir_lower_drsq = (1 << 2),
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nir_lower_dtrunc = (1 << 3),
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} nir_lower_doubles_options;
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void nir_lower_doubles(nir_shader *shader, nir_lower_doubles_options options);
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@@ -299,6 +299,58 @@ lower_sqrt_rsq(nir_builder *b, nir_ssa_def *src, bool sqrt)
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return res;
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}
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static nir_ssa_def *
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lower_trunc(nir_builder *b, nir_ssa_def *src)
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{
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nir_ssa_def *unbiased_exp = nir_isub(b, get_exponent(b, src),
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nir_imm_int(b, 1023));
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nir_ssa_def *frac_bits = nir_isub(b, nir_imm_int(b, 52), unbiased_exp);
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/*
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* Decide the operation to apply depending on the unbiased exponent:
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*
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* if (unbiased_exp < 0)
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* return 0
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* else if (unbiased_exp > 52)
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* return src
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* else
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* return src & (~0 << frac_bits)
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*
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* Notice that the else branch is a 64-bit integer operation that we need
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* to implement in terms of 32-bit integer arithmetics (at least until we
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* support 64-bit integer arithmetics).
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*/
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/* Compute "~0 << frac_bits" in terms of hi/lo 32-bit integer math */
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nir_ssa_def *mask_lo =
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nir_bcsel(b,
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nir_ige(b, frac_bits, nir_imm_int(b, 32)),
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nir_imm_int(b, 0),
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nir_ishl(b, nir_imm_int(b, ~0), frac_bits));
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nir_ssa_def *mask_hi =
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nir_bcsel(b,
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nir_ilt(b, frac_bits, nir_imm_int(b, 33)),
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nir_imm_int(b, ~0),
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nir_ishl(b,
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nir_imm_int(b, ~0),
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nir_isub(b, frac_bits, nir_imm_int(b, 32))));
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nir_ssa_def *src_lo = nir_unpack_double_2x32_split_x(b, src);
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nir_ssa_def *src_hi = nir_unpack_double_2x32_split_y(b, src);
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return
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nir_bcsel(b,
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nir_ilt(b, unbiased_exp, nir_imm_int(b, 0)),
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nir_imm_double(b, 0.0),
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nir_bcsel(b, nir_ige(b, unbiased_exp, nir_imm_int(b, 53)),
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src,
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nir_pack_double_2x32_split(b,
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nir_iand(b, mask_lo, src_lo),
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nir_iand(b, mask_hi, src_hi))));
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}
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static void
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lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options options)
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{
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@@ -322,6 +374,11 @@ lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options options)
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return;
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break;
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case nir_op_ftrunc:
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if (!(options & nir_lower_dtrunc))
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return;
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break;
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default:
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return;
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}
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@@ -345,6 +402,9 @@ lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options options)
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case nir_op_frsq:
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result = lower_sqrt_rsq(&bld, src, false);
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break;
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case nir_op_ftrunc:
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result = lower_trunc(&bld, src);
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break;
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default:
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unreachable("unhandled opcode");
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}
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