Mesa (master): nir/lower_bit_size: optimize upcast of b2i8/b2i16

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Module: Mesa
Branch: master
Commit: 475077c790feeb0b677bd91107ac87711ca468aa
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=475077c790feeb0b677bd91107ac87711ca468aa

Author: Rhys Perry <pendingchaos02 at gmail.com>
Date:   Fri Oct 30 15:18:25 2020 +0000

nir/lower_bit_size: optimize upcast of b2i8/b2i16

This also seems to be done by nir_opt_algebraic, but RADV will be moving
nir_lower_bit_size() to after that (so it doesn't create unsupported
8/16-bit instructions) and it doesn't seem worth creating a new pass just
for this simple optimization.

Signed-off-by: Rhys Perry <pendingchaos02 at gmail.com>
Reviewed-by: Daniel Schürmann <daniel at schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4791>

---

 src/compiler/nir/nir_lower_bit_size.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/compiler/nir/nir_lower_bit_size.c b/src/compiler/nir/nir_lower_bit_size.c
index d145cc1ada1..34bfa3a1d8f 100644
--- a/src/compiler/nir/nir_lower_bit_size.c
+++ b/src/compiler/nir/nir_lower_bit_size.c
@@ -30,6 +30,21 @@
  * the original bit-size.
  */
 
+static nir_ssa_def *convert_to_bit_size(nir_builder *bld, nir_ssa_def *src,
+                                        nir_alu_type type, unsigned bit_size)
+{
+   /* create b2i32(a) instead of i2i32(b2i8(a))/i2i32(b2i16(a)) */
+   nir_alu_instr *alu = nir_src_as_alu_instr(nir_src_for_ssa(src));
+   if ((type & (nir_type_uint | nir_type_int)) && bit_size == 32 &&
+       alu && (alu->op == nir_op_b2i8 || alu->op == nir_op_b2i16)) {
+      nir_alu_instr *instr = nir_alu_instr_create(bld->shader, nir_op_b2i32);
+      nir_alu_src_copy(&instr->src[0], &alu->src[0], instr);
+      return nir_builder_alu_instr_finish_and_insert(bld, instr);
+   }
+
+   return nir_convert_to_bit_size(bld, src, type, bit_size);
+}
+
 static void
 lower_instr(nir_builder *bld, nir_alu_instr *alu, unsigned bit_size)
 {
@@ -45,7 +60,7 @@ lower_instr(nir_builder *bld, nir_alu_instr *alu, unsigned bit_size)
 
       nir_alu_type type = nir_op_infos[op].input_types[i];
       if (nir_alu_type_get_type_size(type) == 0)
-         src = nir_convert_to_bit_size(bld, src, type, bit_size);
+         src = convert_to_bit_size(bld, src, type, bit_size);
 
       if (i == 1 && (op == nir_op_ishl || op == nir_op_ishr || op == nir_op_ushr)) {
          assert(util_is_power_of_two_nonzero(dst_bit_size));