nir: Add nir_lower_alu_to_scalar.

This is the equivalent of brw_fs_channel_expressions.cpp, which I wanted
for vc4.

v2: Use the nir_src_for_ssa() helper, and another instance of
    nir_alu_src_copy().
v3: Drop the non-SSA support.  All intended callers will have SSA-only ALU
    ops.
v4: Use insert_before, drop stale bcsel/fcsel comment, drop now-unused
    unsupported() function, drop lower_context struct.
v5: Completely rename the pass to nir_lower_alu_to_scalar(), add an assert
    about weird input_sizes[].

Reviewed-by: Jason Ekstrand <jason.ekstrand@iastate.edu>

src/glsl/Makefile.sources

@@ -23,6 +23,7 @@ NIR_FILES = \
 	nir/nir_intrinsics.c \
 	nir/nir_intrinsics.h \
 	nir/nir_live_variables.c \
+	nir/nir_lower_alu_to_scalar.c \
 	nir/nir_lower_atomics.c \
 	nir/nir_lower_global_vars_to_local.c \
 	nir/nir_lower_locals_to_regs.c \

src/glsl/nir/nir.h

@@ -1520,6 +1520,7 @@ void nir_lower_vars_to_ssa(nir_shader *shader);
 void nir_remove_dead_variables(nir_shader *shader);
 
 void nir_lower_vec_to_movs(nir_shader *shader);
+void nir_lower_alu_to_scalar(nir_shader *shader);
 
 void nir_lower_samplers(nir_shader *shader,
                         struct gl_shader_program *shader_program,

src/glsl/nir/nir_lower_alu_to_scalar.c

@@ -0,0 +1,186 @@
+/*
+ * Copyright © 2014-2015 Broadcom
+ *
+ * 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 "nir.h"
+
+/** @file nir_lower_alu_to_scalar.c
+ *
+ * Replaces nir_alu_instr operations with more than one channel used in the
+ * arguments with individual per-channel operations.
+ */
+
+static void
+nir_alu_ssa_dest_init(nir_alu_instr *instr, unsigned num_components)
+{
+   nir_ssa_dest_init(&instr->instr, &instr->dest.dest, num_components, NULL);
+   instr->dest.write_mask = (1 << num_components) - 1;
+}
+
+static void
+lower_reduction(nir_alu_instr *instr, nir_op chan_op, nir_op merge_op,
+                void *mem_ctx)
+{
+   unsigned num_components = nir_op_infos[instr->op].input_sizes[0];
+
+   nir_ssa_def *last = NULL;
+   for (unsigned i = 0; i < num_components; i++) {
+      nir_alu_instr *chan = nir_alu_instr_create(mem_ctx, chan_op);
+      nir_alu_ssa_dest_init(chan, 1);
+      nir_alu_src_copy(&chan->src[0], &instr->src[0], mem_ctx);
+      chan->src[0].swizzle[0] = chan->src[0].swizzle[i];
+      if (nir_op_infos[chan_op].num_inputs > 1) {
+         assert(nir_op_infos[chan_op].num_inputs == 2);
+         nir_alu_src_copy(&chan->src[1], &instr->src[1], mem_ctx);
+         chan->src[1].swizzle[0] = chan->src[1].swizzle[i];
+      }
+
+      nir_instr_insert_before(&instr->instr, &chan->instr);
+
+      if (i == 0) {
+         last = &chan->dest.dest.ssa;
+      } else {
+         nir_alu_instr *merge = nir_alu_instr_create(mem_ctx, merge_op);
+         nir_alu_ssa_dest_init(merge, 1);
+         merge->dest.write_mask = 1;
+         merge->src[0].src = nir_src_for_ssa(last);
+         merge->src[1].src = nir_src_for_ssa(&chan->dest.dest.ssa);
+         nir_instr_insert_before(&instr->instr, &merge->instr);
+         last = &merge->dest.dest.ssa;
+      }
+   }
+
+   assert(instr->dest.write_mask == 1);
+   nir_ssa_def_rewrite_uses(&instr->dest.dest.ssa, nir_src_for_ssa(last),
+                            mem_ctx);
+   nir_instr_remove(&instr->instr);
+}
+
+static void
+lower_alu_instr_scalar(nir_alu_instr *instr, void *mem_ctx)
+{
+   unsigned num_src = nir_op_infos[instr->op].num_inputs;
+   unsigned i, chan;
+
+   assert(instr->dest.dest.is_ssa);
+   assert(instr->dest.write_mask != 0);
+
+#define LOWER_REDUCTION(name, chan, merge) \
+   case name##2: \
+   case name##3: \
+   case name##4: \
+      lower_reduction(instr, chan, merge, mem_ctx); \
+      break;
+
+   switch (instr->op) {
+   case nir_op_vec4:
+   case nir_op_vec3:
+   case nir_op_vec2:
+      /* We don't need to scalarize these ops, they're the ones generated to
+       * group up outputs into a value that can be SSAed.
+       */
+      return;
+
+      LOWER_REDUCTION(nir_op_fdot, nir_op_fmul, nir_op_fadd);
+      LOWER_REDUCTION(nir_op_ball_fequal, nir_op_feq, nir_op_iand);
+      LOWER_REDUCTION(nir_op_ball_iequal, nir_op_ieq, nir_op_iand);
+      LOWER_REDUCTION(nir_op_bany_fnequal, nir_op_fne, nir_op_ior);
+      LOWER_REDUCTION(nir_op_bany_inequal, nir_op_ine, nir_op_ior);
+      LOWER_REDUCTION(nir_op_fall_equal, nir_op_seq, nir_op_fand);
+      LOWER_REDUCTION(nir_op_fany_nequal, nir_op_sne, nir_op_for);
+      LOWER_REDUCTION(nir_op_ball, nir_op_imov, nir_op_iand);
+      LOWER_REDUCTION(nir_op_bany, nir_op_imov, nir_op_ior);
+      LOWER_REDUCTION(nir_op_fall, nir_op_fmov, nir_op_fand);
+      LOWER_REDUCTION(nir_op_fany, nir_op_fmov, nir_op_for);
+
+   default:
+      break;
+   }
+
+   if (instr->dest.dest.ssa.num_components == 1)
+      return;
+
+   unsigned num_components = instr->dest.dest.ssa.num_components;
+   static const nir_op nir_op_map[] = {nir_op_vec2, nir_op_vec3, nir_op_vec4};
+   nir_alu_instr *vec_instr =
+      nir_alu_instr_create(mem_ctx, nir_op_map[num_components - 2]);
+   nir_alu_ssa_dest_init(vec_instr, num_components);
+
+   for (chan = 0; chan < 4; chan++) {
+      if (!(instr->dest.write_mask & (1 << chan)))
+         continue;
+
+      nir_alu_instr *lower = nir_alu_instr_create(mem_ctx, instr->op);
+      for (i = 0; i < num_src; i++) {
+         /* We only handle same-size-as-dest (input_sizes[] == 0) or scalar
+          * args (input_sizes[] == 1).
+          */
+         assert(nir_op_infos[instr->op].input_sizes[i] < 2);
+         unsigned src_chan = (nir_op_infos[instr->op].input_sizes[i] == 1 ?
+                              0 : chan);
+
+         nir_alu_src_copy(&lower->src[i], &instr->src[i], mem_ctx);
+         for (int j = 0; j < 4; j++)
+            lower->src[i].swizzle[j] = instr->src[i].swizzle[src_chan];
+      }
+
+      nir_alu_ssa_dest_init(lower, 1);
+      lower->dest.saturate = instr->dest.saturate;
+      vec_instr->src[chan].src = nir_src_for_ssa(&lower->dest.dest.ssa);
+
+      nir_instr_insert_before(&instr->instr, &lower->instr);
+   }
+
+   nir_instr_insert_before(&instr->instr, &vec_instr->instr);
+
+   nir_ssa_def_rewrite_uses(&instr->dest.dest.ssa,
+                            nir_src_for_ssa(&vec_instr->dest.dest.ssa),
+                            mem_ctx);
+
+   nir_instr_remove(&instr->instr);
+}
+
+static bool
+lower_alu_to_scalar_block(nir_block *block, void *data)
+{
+   nir_foreach_instr_safe(block, instr) {
+      if (instr->type == nir_instr_type_alu)
+         lower_alu_instr_scalar((nir_alu_instr *)instr, data);
+   }
+
+   return true;
+}
+
+static void
+nir_lower_alu_to_scalar_impl(nir_function_impl *impl)
+{
+   nir_foreach_block(impl, lower_alu_to_scalar_block, ralloc_parent(impl));
+}
+
+void
+nir_lower_alu_to_scalar(nir_shader *shader)
+{
+   nir_foreach_overload(shader, overload) {
+      if (overload->impl)
+         nir_lower_alu_to_scalar_impl(overload->impl);
+   }
+}