intel/fs: Introduce barycentric layout lowering pass.

The goal is to represent barycentrics with the standard vector layout
during optimization and particularly SIMD lowering.  Instead of
emitting the barycentric layout conversions at NIR translation time,
do it later as a lowering pass.  For the moment this is only applied
to PI messages, but we'll give the same treatment to LINTERP
instructions too.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/intel/compiler/brw_fs.cpp

@@ -6733,6 +6733,72 @@ fs_visitor::lower_simd_width()
    return progress;
 }
 
+/**
+ * Transform barycentric vectors into the interleaved form expected by the PLN
+ * instruction and returned by the Gen7+ PI shared function.
+ *
+ * For channels 0-15 in SIMD16 mode they are expected to be laid out as
+ * follows in the register file:
+ *
+ *    rN+0: X[0-7]
+ *    rN+1: Y[0-7]
+ *    rN+2: X[8-15]
+ *    rN+3: Y[8-15]
+ *
+ * There is no need to handle SIMD32 here -- This is expected to be run after
+ * SIMD lowering, since SIMD lowering relies on vectors having the standard
+ * component layout.
+ */
+bool
+fs_visitor::lower_barycentrics()
+{
+   const bool has_interleaved_layout = devinfo->has_pln || devinfo->gen >= 7;
+   bool progress = false;
+
+   if (stage != MESA_SHADER_FRAGMENT || !has_interleaved_layout)
+      return false;
+
+   foreach_block_and_inst_safe(block, fs_inst, inst, cfg) {
+      if (inst->exec_size < 16)
+         continue;
+
+      const fs_builder ibld(this, block, inst);
+      const fs_builder ubld = ibld.exec_all().group(8, 0);
+
+      switch (inst->opcode) {
+      case FS_OPCODE_INTERPOLATE_AT_SAMPLE:
+      case FS_OPCODE_INTERPOLATE_AT_SHARED_OFFSET:
+      case FS_OPCODE_INTERPOLATE_AT_PER_SLOT_OFFSET: {
+         assert(inst->exec_size == 16);
+         const fs_reg tmp = ibld.vgrf(inst->dst.type, 2);
+
+         for (unsigned i = 0; i < 2; i++) {
+            for (unsigned g = 0; g < inst->exec_size / 8; g++) {
+               fs_inst *mov = ibld.at(block, inst->next).group(8, g)
+                                  .MOV(horiz_offset(offset(inst->dst, ibld, i),
+                                                    8 * g),
+                                       offset(tmp, ubld, 2 * g + i));
+               mov->predicate = inst->predicate;
+               mov->predicate_inverse = inst->predicate_inverse;
+               mov->flag_subreg = inst->flag_subreg;
+            }
+         }
+
+         inst->dst = tmp;
+         progress = true;
+         break;
+      }
+      default:
+         break;
+      }
+   }
+
+   if (progress)
+      invalidate_live_intervals();
+
+   return progress;
+}
+
 void
 fs_visitor::dump_instructions()
 {
@@ -7252,6 +7318,7 @@ fs_visitor::optimize()
    }
 
    OPT(lower_simd_width);
+   OPT(lower_barycentrics);
 
    /* After SIMD lowering just in case we had to unroll the EOT send. */
    OPT(opt_sampler_eot);