Some conversions are not directly supported in hardware and need to be
split in two conversion instructions going through an intermediary type.
Doing this at the NIR level simplifies a bit the complexity in the backend.
v2:
- Consider fp16 rounding conversion opcodes
- Properly handle swizzles on conversion sources.
v3
- Run the pass earlier, right after nir_opt_algebraic_late (Jason)
- NIR alu output types already have the bit-size (Jason)
- Use 'is_conversion' to identify conversion operations (Jason)
v4:
- Be careful about the intermediate types we use so we don't lose
range and avoid incorrect rounding semantics (Jason)
Reviewed-by: Topi Pohjolainen <topi.pohjolai...@intel.com> (v1)
---
src/intel/Makefile.sources | 1 +
src/intel/compiler/brw_nir.c | 2 +
src/intel/compiler/brw_nir.h | 2 +
.../compiler/brw_nir_lower_conversions.c | 169 ++++++++++++++++++
src/intel/compiler/meson.build | 1 +
5 files changed, 175 insertions(+)
create mode 100644 src/intel/compiler/brw_nir_lower_conversions.c
diff --git a/src/intel/Makefile.sources b/src/intel/Makefile.sources
index 94a28d370e8..9975daa3ad1 100644
--- a/src/intel/Makefile.sources
+++ b/src/intel/Makefile.sources
@@ -83,6 +83,7 @@ COMPILER_FILES = \
compiler/brw_nir_analyze_boolean_resolves.c \
compiler/brw_nir_analyze_ubo_ranges.c \
compiler/brw_nir_attribute_workarounds.c \
+ compiler/brw_nir_lower_conversions.c \
compiler/brw_nir_lower_cs_intrinsics.c \
compiler/brw_nir_lower_image_load_store.c \
compiler/brw_nir_lower_mem_access_bit_sizes.c \
diff --git a/src/intel/compiler/brw_nir.c b/src/intel/compiler/brw_nir.c
index 9dbf06004a4..7e3dbc9e447 100644
--- a/src/intel/compiler/brw_nir.c
+++ b/src/intel/compiler/brw_nir.c
@@ -876,6 +876,8 @@ brw_postprocess_nir(nir_shader *nir, const struct
brw_compiler *compiler,
OPT(nir_opt_algebraic_late);
+ OPT(brw_nir_lower_conversions);
+
OPT(nir_lower_to_source_mods, nir_lower_all_source_mods);
OPT(nir_copy_prop);
OPT(nir_opt_dce);
diff --git a/src/intel/compiler/brw_nir.h b/src/intel/compiler/brw_nir.h
index bc81950d47e..662b2627e95 100644
--- a/src/intel/compiler/brw_nir.h
+++ b/src/intel/compiler/brw_nir.h
@@ -114,6 +114,8 @@ void brw_nir_lower_tcs_outputs(nir_shader *nir, const
struct brw_vue_map *vue,
GLenum tes_primitive_mode);
void brw_nir_lower_fs_outputs(nir_shader *nir);
+bool brw_nir_lower_conversions(nir_shader *nir);
+
bool brw_nir_lower_image_load_store(nir_shader *nir,
const struct gen_device_info *devinfo);
void brw_nir_rewrite_image_intrinsic(nir_intrinsic_instr *intrin,
diff --git a/src/intel/compiler/brw_nir_lower_conversions.c
b/src/intel/compiler/brw_nir_lower_conversions.c
new file mode 100644
index 00000000000..9aff30b568b
--- /dev/null
+++ b/src/intel/compiler/brw_nir_lower_conversions.c
@@ -0,0 +1,169 @@
+/*
+ * Copyright © 2018 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include "brw_nir.h"
+#include "compiler/nir/nir_builder.h"
+
+static nir_op
+get_conversion_op(nir_alu_type src_type,
+ unsigned src_bit_size,
+ nir_alu_type dst_type,
+ unsigned dst_bit_size,
+ nir_rounding_mode rounding_mode)
+{
+ nir_alu_type src_full_type = (nir_alu_type) (src_type | src_bit_size);
+ nir_alu_type dst_full_type = (nir_alu_type) (dst_type | dst_bit_size);
+
+ return nir_type_conversion_op(src_full_type, dst_full_type, rounding_mode);
+}
+
+static nir_rounding_mode
+get_opcode_rounding_mode(nir_op op)
+{
+ switch (op) {
+ case nir_op_f2f16_rtz:
+ return nir_rounding_mode_rtz;
+ case nir_op_f2f16_rtne:
+ return nir_rounding_mode_rtne;
+ default:
+ return nir_rounding_mode_undef;
+ }
+}
+
+static void
+split_conversion(nir_builder *b, nir_alu_instr *alu, nir_op op1, nir_op op2)
+{
+ b->cursor = nir_before_instr(&alu->instr);
+ assert(alu->dest.write_mask == 1);
+ nir_ssa_def *src = nir_ssa_for_alu_src(b, alu, 0);
+ nir_ssa_def *tmp = nir_build_alu(b, op1, src, NULL, NULL, NULL);
+ nir_ssa_def *res = nir_build_alu(b, op2, tmp, NULL, NULL, NULL);
+ nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(res));
+ nir_instr_remove(&alu->instr);
+}
+
+static bool
+lower_instr(nir_builder *b, nir_alu_instr *alu)
+{
+ unsigned src_bit_size = nir_src_bit_size(alu->src[0].src);
+ nir_alu_type src_type = nir_op_infos[alu->op].input_types[0];
+ nir_alu_type src_full_type = (nir_alu_type) (src_type | src_bit_size);
+
+ unsigned dst_bit_size = nir_dest_bit_size(alu->dest.dest);
+ nir_alu_type dst_full_type = nir_op_infos[alu->op].output_type;
+ nir_alu_type dst_type = nir_alu_type_get_base_type(dst_full_type);
+
+ /* BDW PRM, vol02, Command Reference Instructions, mov - MOVE:
+ *
+ * "There is no direct conversion from HF to DF or DF to HF.
+ * Use two instructions and F (Float) as an intermediate type.
+ *
+ * There is no direct conversion from HF to Q/UQ or Q/UQ to HF.
+ * Use two instructions and F (Float) or a word integer type
+ * or a DWord integer type as an intermediate type."
+ *
+ * It is important that the intermediate conversion happens through a
+ * 32-bit float type so we don't lose range when we convert from
+ * a 64-bit integer.
+ */
+ if ((src_full_type == nir_type_float16 && dst_bit_size == 64) ||
+ (src_bit_size == 64 && dst_full_type == nir_type_float16)) {
+ nir_op op1 = get_conversion_op(src_type, src_bit_size,
+ nir_type_float, 32,
+ nir_rounding_mode_undef);
+ nir_op op2 = get_conversion_op(nir_type_float, 32,
+ dst_type, dst_bit_size,
+ get_opcode_rounding_mode(alu->op));
+ split_conversion(b, alu, op1, op2);
+ return true;
+ }
+
+ /* SKL PRM, vol 02a, Command Reference: Instructions, Move:
+ *
+ * "There is no direct conversion from B/UB to DF or DF to B/UB. Use
+ * two instructions and a word or DWord intermediate type."
+ *
+ * "There is no direct conversion from B/UB to Q/UQ or Q/UQ to B/UB.
+ * Use two instructions and a word or DWord intermediate integer
+ * type."
+ *
+ * It is important that we use a 32-bit integer matching the sign of the
+ * destination as the intermediate type so we avoid any chance of rtne
+ * rounding happening before the conversion to integer (which is expected
+ * to round towards zero) in double to byte conversions.
+ */
+ if ((src_bit_size == 8 && dst_bit_size == 64) ||
+ (src_bit_size == 64 && dst_bit_size == 8)) {
+ nir_op op1 = get_conversion_op(src_type, src_bit_size, dst_type, 32,
+ nir_rounding_mode_undef);
+ nir_op op2 = get_conversion_op(dst_type, 32, dst_type, dst_bit_size,
+ nir_rounding_mode_undef);
+ split_conversion(b, alu, op1, op2);
+ return true;
+ }
+
+ return false;
+}
+
+static bool
+lower_impl(nir_function_impl *impl)
+{
+ nir_builder b;
+ nir_builder_init(&b, impl);
+ bool progress = false;
+
+ nir_foreach_block(block, impl) {
+ nir_foreach_instr_safe(instr, block) {
+ if (instr->type != nir_instr_type_alu)
+ continue;
+
+ nir_alu_instr *alu = nir_instr_as_alu(instr);
+ assert(alu->dest.dest.is_ssa);
+
+ if (!nir_op_infos[alu->op].is_conversion)
+ continue;
+
+ progress = lower_instr(&b, alu) || progress;
+ }
+ }
+
+ if (progress) {
+ nir_metadata_preserve(impl, nir_metadata_block_index |
+ nir_metadata_dominance);
+ }
+
+ return progress;
+}
+
+bool
+brw_nir_lower_conversions(nir_shader *shader)
+{
+ bool progress = false;
+
+ nir_foreach_function(function, shader) {
+ if (function->impl)
+ progress |= lower_impl(function->impl);
+ }
+
+ return progress;
+}
diff --git a/src/intel/compiler/meson.build b/src/intel/compiler/meson.build
index f8e5e2518fe..9daf2a94260 100644
--- a/src/intel/compiler/meson.build
+++ b/src/intel/compiler/meson.build
@@ -76,6 +76,7 @@ libintel_compiler_files = files(
'brw_nir_analyze_boolean_resolves.c',
'brw_nir_analyze_ubo_ranges.c',
'brw_nir_attribute_workarounds.c',
+ 'brw_nir_lower_conversions.c',
'brw_nir_lower_cs_intrinsics.c',
'brw_nir_lower_image_load_store.c',
'brw_nir_lower_mem_access_bit_sizes.c',
--
2.17.1
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