[Mesa-dev] [PATCH] nir: fix condition propagation when src has a swizzle

[Timothy Arceri]

We cannot use nir_build_alu() to create the new alu as it has no
way to know how many components of the src we will use. This
results in it guessing the max number of components from one of
its inputs.

Fixes the following CTS tests:

dEQP-VK.spirv_assembly.instruction.graphics.selection_block_order.out_of_order_frag
dEQP-VK.spirv_assembly.instruction.graphics.selection_block_order.out_of_order_geom
dEQP-VK.spirv_assembly.instruction.graphics.selection_block_order.out_of_order_tessc
dEQP-VK.spirv_assembly.instruction.graphics.selection_block_order.out_of_order_vert

Fixes: 2975422ceb6c ("nir: propagates if condition evaluation down some alu chains")
---

I'm running this in Intel CI currently but it hasn't been giving me proper results
today so fingers crossed.

 src/compiler/nir/nir_opt_if.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c
index ed93cac9ce9..1eb49a64aba 100644
--- a/src/compiler/nir/nir_opt_if.c
+++ b/src/compiler/nir/nir_opt_if.c
@@ -391,6 +391,34 @@ evaluate_if_condition(nir_if *nif, nir_cursor cursor, bool *value)
    }
 }
 
+static nir_ssa_def *
+clone_alu_and_replace_src_defs(nir_builder *b, const nir_alu_instr *alu,
+                               nir_ssa_def **src_defs)
+{
+   nir_alu_instr *nalu = nir_alu_instr_create(b->shader, alu->op);
+   nalu->exact = alu->exact;
+
+   nir_ssa_dest_init(&nalu->instr, &nalu->dest.dest,
+                     alu->dest.dest.ssa.num_components,
+                     alu->dest.dest.ssa.bit_size, alu->dest.dest.ssa.name);
+
+   nalu->dest.saturate = alu->dest.saturate;
+   nalu->dest.write_mask = alu->dest.write_mask;
+
+   for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
+      nalu->src[i].src.is_ssa = alu->src[i].src.is_ssa;
+      nalu->src[i].src.ssa = src_defs[i];
+      nalu->src[i].negate = alu->src[i].negate;
+      nalu->src[i].abs = alu->src[i].abs;
+      memcpy(nalu->src[i].swizzle, alu->src[i].swizzle,
+             sizeof(nalu->src[i].swizzle));
+   }
+
+   nir_builder_instr_insert(b, &nalu->instr);
+
+   return &nalu->dest.dest.ssa;;
+}
+
 /*
  * This propagates if condition evaluation down the chain of some alu
  * instructions. For example by checking the use of some of the following alu
@@ -456,7 +484,8 @@ propagate_condition_eval(nir_builder *b, nir_if *nif, nir_src *use_src,
          def[i] = alu->src[i].src.ssa;
       }
    }
-   nir_ssa_def *nalu = nir_build_alu(b, alu->op, def[0], def[1], def[2], def[3]);
+
+   nir_ssa_def *nalu = clone_alu_and_replace_src_defs(b, alu, def);
 
    /* Rewrite use to use new alu instruction */
    nir_src new_src = nir_src_for_ssa(nalu);
-- 
2.19.1